dfs-and-similar

Practice › Codeforces Solutions › Codeforces Round 740 (Div. 1, based on VK Cup 2021 - Final (Engine)) ›

CF 1558E - Down Below

CF 1558E - Down Below Rating: 3000 Tags: binary search, dfs and similar, graphs, greedy, meet-in-the-middle, shortest paths Solve time: 1m 49s Verified: no Solution Problem Understanding We are given a graph of caves connected by tunnels, and a hero who starts at cave 1 with some initial power. Every other cave initially contains a monster. The hero’s task is to visit and defeat the monster in every cave at...

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CF 1552D - Array Differentiation

CF 1552D - Array Differentiation Rating: 1800 Tags: bitmasks, brute force, constructive algorithms, dfs and similar, dp, graphs, math Solve time: 5m 22s Verified: no Solution Problem Understanding We are given a list of integers, and we want to decide whether it is possible to assign another list of the same length, say $b_1, b_2, \dots, b_n$, such that every given number $a_i$ can be expressed as a difference between...

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CF 1552I - Organizing a Music Festival

CF 1552I - Organizing a Music Festival Rating: 3400 Tags: dfs and similar, math Solve time: 2m 3s Verified: yes Solution Problem Understanding We are asked to count how many permutations of singers are valid under a set of “group contiguity” constraints. Each singer is a distinct element from $1$ to $n$. We must arrange all of them in a line. Each friend gives us a subset of singers they...

Practice › Codeforces Solutions › Educational Codeforces Round 92 (Rated for Div. 2) ›

CF 1389G - Directing Edges

CF 1389G - Directing Edges Rating: 2800 Tags: dfs and similar, dp, graphs, trees Solve time: 2m 35s Verified: no Solution Problem Understanding We are given an undirected connected graph where each edge can be turned into a one-way edge of our choosing or kept as a two-way edge. Keeping it two-way is expensive, since every such edge contributes its weight to the cost. Directed edges are free but only...

Practice › Codeforces Solutions › Codeforces Round 656 (Div. 3) ›

CF 1385E - Directing Edges

CF 1385E - Directing Edges Rating: 2000 Tags: constructive algorithms, dfs and similar, graphs Solve time: 5m 5s Verified: no Solution Problem Understanding We are given a graph where every edge already knows its endpoints, but not all edges are allowed to choose their direction freely. Some edges are already directed and must stay exactly as they are, while the remaining edges are undirected and can be oriented however we...

Practice › Codeforces Solutions › Codeforces Round 656 (Div. 3) ›

CF 1385G - Columns Swaps

CF 1385G - Columns Swaps Rating: 2300 Tags: 2-sat, dfs and similar, dsu, graphs, implementation Solve time: 1m 35s Verified: no Solution Problem Understanding We are given a two-row table with $n$ columns, and every cell contains a number between $1$ and $n$. In each column we are allowed to either leave the two values as they are or swap them, and each column can be swapped at most once....

Practice › Codeforces Solutions › Codeforces Round 650 (Div. 3) ›

CF 1367E - Necklace Assembly

CF 1367E - Necklace Assembly Rating: 1900 Tags: brute force, dfs and similar, dp, graphs, greedy, number theory Solve time: 1m 8s Verified: yes Solution Problem Understanding We are given a multiset of colored beads, where each bead is just a lowercase letter. From these beads, we want to choose some subset and arrange it in a circle, forming a necklace. The arrangement is circular, so rotations matter but there...

Practice › Codeforces Solutions › Codeforces Round 621 (Div. 1 + Div. 2) ›

CF 1307F - Cow and Vacation

CF 1307F - Cow and Vacation Rating: 3300 Tags: dfs and similar, dsu, trees Solve time: 3m 17s Verified: no Solution Problem Understanding We are working on a tree of cities connected by roads, where every pair of cities is reachable through a unique simple path. Some of these cities contain rest stops. Bessie wants to travel between pairs of cities, but she has a constraint: she cannot traverse more...

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CF 1266F - Almost Same Distance

CF 1266F - Almost Same Distance Rating: 2900 Tags: dfs and similar, graphs Solve time: 1m 59s Verified: no Solution Problem Understanding We are given a tree, and for every possible distance value $k$, we want to know how large a subset of vertices we can pick such that every pair of chosen vertices is “almost equidistant” in a very strict sense: if you pick any two vertices in the...

Practice › Codeforces Solutions › 2019-2020 ICPC, NERC, Southern and Volga Russian Regional Contest (Online Mirror, ICPC Rules, Teams Preferred) ›

CF 1250N - Wires

CF 1250N - Wires Rating: 2000 Tags: dfs and similar, graphs, greedy Solve time: 2m Verified: no Solution Problem Understanding Each wire connects two contact points, and we say two wires are related if they share at least one endpoint, or if there is a chain of wires where consecutive wires share endpoints. This creates a notion of connectivity over the wires themselves: wires are nodes, and sharing a contact...

Practice › Codeforces Solutions › Codeforces Round 599 (Div. 1) ›

CF 1242C - Sum Balance

CF 1242C - Sum Balance Rating: 2400 Tags: bitmasks, dfs and similar, dp, graphs Solve time: 1m 43s Verified: no Solution Problem Understanding We are given several containers, each holding a multiset of distinct integers. A single operation is performed exactly once: from every container, we must pick exactly one value, and then redistribute those chosen values back into the containers so that each container still ends up with the...

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Codeforces Round 449 (Div. 1)

Codeforces Round 449 (Div. 1) Div. 1 | 1 problems | 1/1 verified | Difficulty 1700-1700 | 3m 28s # Problem Rating Tags Accepted Time ✓ A Nephren gives a riddle 1700 binary-search, dfs-and-similar 3,793 3m 28s ✓

Practice › Codeforces Solutions › Codeforces Round 449 (Div. 1) ›

CF 896A - Nephren gives a riddle

CF 896A - Nephren gives a riddle Rating: 1700 Tags: binary search, dfs and similar Solve time: 3m 28s Verified: yes Solution Problem Understanding The construction in this problem generates a sequence of strings where each level wraps the previous one inside a fixed template. The base string, call it $f_0$, is a fixed sentence. Every next string $f_i$ is formed by taking a fixed outer sentence pattern and inserting...

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Codeforces Round 468 (Div. 1, based on Technocup 2018 Final Round)

Codeforces Round 468 (Div. 1, based on Technocup 2018 Final Round) Div. 1 | 3 problems | 2/3 verified | Difficulty 1500-2900 | 4m 58s # Problem Rating Tags Accepted Time ✓ A Peculiar apple-tree 1500 dfs-and-similar, graphs, trees 8,386 1m 10s ✓ C Teodor is not a liar! 1900 data-structures, dp 2,373 1m 52s ✓ E Coins Exhibition 2900 data-structures, dp, math 519 1m 56s

Practice › Codeforces Solutions › Codeforces Round 468 (Div. 1, based on Technocup 2018 Final Round) ›

CF 930A - Peculiar apple-tree

CF 930A - Peculiar apple-tree Rating: 1500 Tags: dfs and similar, graphs, trees Solve time: 1m 10s Verified: yes Solution Problem Understanding We are given a rooted tree with vertices numbered from 1 to n, where vertex 1 is the root. Every vertex i greater than 1 has exactly one parent p[i], and that parent always has a smaller index, which implicitly guarantees that the structure is a rooted tree...

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Codeforces Round 467 (Div. 1)

Codeforces Round 467 (Div. 1) Div. 1 | 2 problems | 0/2 verified | Difficulty 2100-2300 | 4m 52s # Problem Rating Tags Accepted Time ✓ B Sleepy Game 2100 dfs-and-similar, dp, games 3,411 1m 40s C Lock Puzzle 2300 constructive-algorithms, implementation, strings 1,259 3m 12s

Practice › Codeforces Solutions › Codeforces Round 467 (Div. 1) ›

CF 936B - Sleepy Game

CF 936B - Sleepy Game Rating: 2100 Tags: dfs and similar, dp, games, graphs Solve time: 1m 40s Verified: no Solution Problem Understanding We are given a directed graph where each vertex represents a state of a game token. A token starts at a fixed vertex, and two players alternate moving it along outgoing edges. A player loses immediately if they are to move from a vertex that has no...

Practice › Codeforces Solutions › Codeforces Round 470 (rated, Div. 2, based on VK Cup 2018 Round 1) ›

CF 948A - Protect Sheep

CF 948A - Protect Sheep Rating: 900 Tags: brute force, dfs and similar, graphs, implementation Solve time: 1m 20s Verified: no Solution Problem Understanding The grid can be viewed as a rectangular graph where each cell is a node connected to its four orthogonal neighbors. Some nodes contain sheep, some contain wolves, and the rest are empty. Wolves are free to move step by step across empty cells, but they...

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Codeforces Round 470 (rated, Div. 2, based on VK Cup 2018 Round 1)

Codeforces Round 470 (rated, Div. 2, based on VK Cup 2018 Round 1) Div. 2 | 1 problems | 0/1 verified | Difficulty 900-900 | 1m 20s # Problem Rating Tags Accepted Time ✓ A Protect Sheep 900 brute-force, dfs-and-similar, graphs 15,314 1m 20s

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Codeforces Round 469 (Div. 1)

Codeforces Round 469 (Div. 1) Div. 1 | 6 problems | 2/6 verified | Difficulty 1600-3300 | 14m 46s # Problem Rating Tags Accepted Time ✓ A Zebras 1600 greedy 5,655 1m 32s B A Leapfrog in the Array 1700 constructive-algorithms, math 3,833 1m 32s C Data Center Maintenance 1900 dfs-and-similar, graphs 2,252 5m 25s D Curfew 2300 binary-search, brute-force, greedy 881 3m 41s E Binary Cards 2700 brute-force 769...

Practice › Codeforces Solutions › Codeforces Round 469 (Div. 1) ›

CF 949C - Data Center Maintenance

CF 949C - Data Center Maintenance Rating: 1900 Tags: dfs and similar, graphs Solve time: 5m 25s Verified: no Solution

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Helvetic Coding Contest 2018 online mirror (teams allowed, unrated)

Helvetic Coding Contest 2018 online mirror (teams allowed, unrated) Special | 7 problems | 3/7 verified | Difficulty 1500-3100 | 12m 46s # Problem Rating Tags Accepted Time ✓ A2 Death Stars (medium) 2000 hashing, strings 1,058 1m 31s ✓ A3 Death Stars (hard) 3100 53 59s ✓ B2 Maximum Control (medium) 2200 data-structures, dfs-and-similar, graphs 747 2m 35s C2 Encryption (medium) 2000 dp 1,378 1m 26s E1 Guard Duty...

Practice › Codeforces Solutions › Helvetic Coding Contest 2018 online mirror (teams allowed, unrated) ›

CF 958B2 - Maximum Control (medium)

CF 958B2 - Maximum Control (medium) Rating: 2200 Tags: data structures, dfs and similar, graphs, greedy, trees Solve time: 2m 35s Verified: no Solution Problem Understanding We are given a tree with $N$ nodes, meaning every pair of nodes is connected by exactly one simple path. We are allowed to choose $K$ nodes as “active stations”. Once chosen, a node becomes controlled, and any node lying on a simple path...

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Divide by Zero 2018 and Codeforces Round 474 (Div. 1 + Div. 2, combined)

Divide by Zero 2018 and Codeforces Round 474 (Div. 1 + Div. 2, combined) Div. 1+2 | 4 problems | 3/4 verified | Difficulty 1200-2900 | 6m 51s # Problem Rating Tags Accepted Time ✓ A Check the string 1200 implementation 8,786 1m 4s ✓ B Minimize the error 1500 data-structures, greedy, sortings 12,382 1m 14s ✓ E Alternating Tree 2300 combinatorics, dfs-and-similar, divide-and-conquer 2,269 2m 1s G Bandit Blues...

Practice › Codeforces Solutions › Divide by Zero 2018 and Codeforces Round 474 (Div. 1 + Div. 2, combined) ›

CF 960E - Alternating Tree

CF 960E - Alternating Tree Rating: 2300 Tags: combinatorics, dfs and similar, divide and conquer, dp, probabilities, trees Solve time: 2m 1s Verified: no Solution Problem Understanding We are given a tree with a value attached to every node. Between any two nodes $u$ and $v$, there is exactly one simple path, and we assign a score to that directed path by taking the node values along the path and...

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Educational Codeforces Round 42 (Rated for Div. 2)

Educational Codeforces Round 42 (Rated for Div. 2) Div. 2 | 4 problems | 3/4 verified | Difficulty 1300-2800 | 4m 22s # Problem Rating Tags Accepted Time ✓ A Equator 1300 implementation 13,431 1m 14s ✓ C Make a Square 1400 brute-force, implementation, math 8,357 1m 20s ✓ F Simple Cycles Edges 2400 dfs-and-similar, graphs, trees 1,581 1m 16s ✓ G Visible Black Areas 2800 data-structures, dsu, geometry 207...

Practice › Codeforces Solutions › Educational Codeforces Round 42 (Rated for Div. 2) ›

CF 962F - Simple Cycles Edges

CF 962F - Simple Cycles Edges Rating: 2400 Tags: dfs and similar, graphs, trees Solve time: 1m 16s Verified: yes Solution Problem Understanding We are given an undirected simple graph and asked to identify which edges are “exclusive” to a single simple cycle. In other words, for each edge we want to know whether there exists exactly one cycle in the entire graph that contains this edge, where cycles are...

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Tinkoff Internship Warmup Round 2018 and Codeforces Round 475 (Div. 1)

Tinkoff Internship Warmup Round 2018 and Codeforces Round 475 (Div. 1) Div. 1 | 2 problems | 1/2 verified | Difficulty 2000-2600 | 3m 1s # Problem Rating Tags Accepted Time ✓ B Destruction of a Tree 2000 constructive-algorithms, dfs-and-similar, dp 3,000 1m 22s C Cutting Rectangle 2600 brute-force, math, number-theory 672 1m 39s ✓

Practice › Codeforces Solutions › Tinkoff Internship Warmup Round 2018 and Codeforces Round 475 (Div. 1) ›

CF 963B - Destruction of a Tree

CF 963B - Destruction of a Tree Rating: 2000 Tags: constructive algorithms, dfs and similar, dp, greedy, trees Solve time: 1m 22s Verified: no Solution Problem Understanding We are given a tree where each vertex has an associated current degree that changes as vertices are removed. A vertex is eligible for removal only when its degree is even at the moment we choose it. When a vertex is removed, all...

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Codeforces Round 479 (Div. 3)

Codeforces Round 479 (Div. 3) Div. 3 | 5 problems | 3/5 verified | Difficulty 800-1700 | 6m 59s # Problem Rating Tags Accepted Time ✓ A Wrong Subtraction 800 implementation 217,381 1m 11s ✓ B Two-gram 900 implementation, strings 49,745 1m 15s C Less or Equal 1200 sortings 43,322 1m 33s ✓ D Divide by three, multiply by two 1400 dfs-and-similar, math, sortings 20,523 1m 26s ✓ F Consecutive...

Practice › Codeforces Solutions › Codeforces Round 479 (Div. 3) ›

CF 977D - Divide by three, multiply by two

CF 977D - Divide by three, multiply by two Rating: 1400 Tags: dfs and similar, math, sortings Solve time: 1m 26s Verified: yes Solution Problem Understanding We are given a multiset of integers that originally came from a single starting value that Polycarp repeatedly transformed. Each transformation either doubles the current number or divides it by three when it is divisible. After applying these operations exactly $n-1$ times, we observe...

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Codeforces Round 482 (Div. 2)

Codeforces Round 482 (Div. 2) Div. 2 | 5 problems | 2/5 verified | Difficulty 1000-2400 | 8m 57s # Problem Rating Tags Accepted Time ✓ A Pizza, Pizza, Pizza!!! 1000 math 14,574 1m 6s ✓ B Treasure Hunt 1800 greedy 4,779 1m 14s ✓ C Kuro and Walking Route 1600 dfs-and-similar, trees 7,333 2m 52s D Kuro and GCD and XOR and SUM 2200 binary-search, bitmasks, brute-force 2,176 1m...

Practice › Codeforces Solutions › Codeforces Round 482 (Div. 2) ›

CF 979C - Kuro and Walking Route

CF 979C - Kuro and Walking Route Rating: 1600 Tags: dfs and similar, trees Solve time: 2m 52s Verified: no Solution Problem Understanding We are given a tree, meaning a connected graph with exactly one simple path between any two towns. Every ordered pair of distinct towns defines a walking route that follows that unique path. Among all possible ordered pairs of towns, some are considered invalid. The restriction depends...

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Codeforces Round 484 (Div. 2)

Codeforces Round 484 (Div. 2) Div. 2 | 3 problems | 3/3 verified | Difficulty 1200-2600 | 3m 50s # Problem Rating Tags Accepted Time ✓ A Row 1200 brute-force, constructive-algorithms 9,711 1m 2s ✓ C Cut 'em all! 1500 dfs-and-similar, dp, graphs 15,845 1m 21s ✓ E Billiard 2600 geometry, number-theory 827 1m 27s ✓

Practice › Codeforces Solutions › Codeforces Round 484 (Div. 2) ›

CF 982C - Cut 'em all!

CF 982C - Cut 'em all! Rating: 1500 Tags: dfs and similar, dp, graphs, greedy, trees Solve time: 1m 21s Verified: yes Solution Problem Understanding We are given a tree, meaning a connected graph with no cycles, and every edge is available for us to potentially remove. The operation we are allowed to perform is cutting edges so that the graph splits into smaller connected components. After performing some set...

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Codeforces Round 490 (Div. 3)

Codeforces Round 490 (Div. 3) Div. 3 | 3 problems | 3/3 verified | Difficulty 800-2000 | 3m 43s # Problem Rating Tags Accepted Time ✓ A Mishka and Contest 800 brute-force, implementation 25,323 1m 20s ✓ B Reversing Encryption 900 implementation 19,432 1m 8s ✓ E Reachability from the Capital 2000 dfs-and-similar, graphs, greedy 7,846 1m 15s ✓

Practice › Codeforces Solutions › Codeforces Round 490 (Div. 3) ›

CF 999E - Reachability from the Capital

CF 999E - Reachability from the Capital Rating: 2000 Tags: dfs and similar, graphs, greedy Solve time: 1m 15s Verified: yes Solution Problem Understanding We are given a directed graph where cities are nodes and roads are one-way edges. One city is designated as the capital. The goal is to ensure that every city can be reached by following directed roads starting from the capital. If a city is not...

Practice › Codeforces Solutions › Codeforces Round 496 (Div. 3) ›

CF 1005F - Berland and the Shortest Paths

CF 1005F - Berland and the Shortest Paths Rating: 2100 Tags: brute force, dfs and similar, graphs, shortest paths Solve time: 3m 7s Verified: yes Solution Problem Understanding We are given a connected undirected graph of cities where city 1 is the capital. From this graph we must select exactly $n-1$ roads so that the selected edges still connect all cities, meaning they form a spanning tree. Among all spanning...

Practice › Codeforces Solutions › Codeforces Round 498 (Div. 3) ›

CF 1006E - Military Problem

CF 1006E - Military Problem Rating: 1600 Tags: dfs and similar, graphs, trees Solve time: 1m 26s Verified: yes Solution Problem Understanding We are given a rooted tree of officers where each officer has a unique direct superior except the root officer 1. This creates a hierarchy where every node represents an officer and edges point from superior to subordinate. Each query asks us to simulate a very specific traversal...

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Codeforces Round 499 (Div. 1)

Codeforces Round 499 (Div. 1) Div. 1 | 6 problems | 4/6 verified | Difficulty 1500-3400 | 15m 26s # Problem Rating Tags Accepted Time ✓ A Fly 1500 binary-search, math 9,003 1m 41s ✓ B Rocket 1800 binary-search, interactive 6,386 2m 23s C Border 1800 number-theory 5,930 4m 4s ✓ D Mars rover 2000 dfs-and-similar, graphs, implementation 2,563 1m 48s ✓ E Store 2700 data-structures 386 2m 29s ✓...

Practice › Codeforces Solutions › Codeforces Round 499 (Div. 1) ›

CF 1010D - Mars rover

CF 1010D - Mars rover Rating: 2000 Tags: dfs and similar, graphs, implementation, trees Solve time: 1m 48s Verified: yes Solution Problem Understanding The structure we are given is a rooted tree where every node behaves like a logic component. Leaves are fixed boolean inputs, while internal nodes compute boolean values from their children using standard gates such as AND, OR, XOR, and NOT. The root node produces the final...

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Codeforces Round 500 (Div. 1) [based on EJOI]

Codeforces Round 500 (Div. 1) [based on EJOI] Div. 1 | 6 problems | 3/6 verified | Difficulty 1500-3400 | 15m 11s # Problem Rating Tags Accepted Time ✓ A Photo of The Sky 1500 brute-force, implementation, math 6,689 1m 29s ✓ B Chemical table 1900 constructive-algorithms, dfs-and-similar, dsu 4,385 1m 39s ✓ C Hills 1900 dp 3,827 2m 10s D AB-Strings 2800 constructive-algorithms, strings 426 2m 15s E Cycle...

Practice › Codeforces Solutions › Codeforces Round 500 (Div. 1) [based on EJOI] ›

CF 1012B - Chemical table

CF 1012B - Chemical table Rating: 1900 Tags: constructive algorithms, dfs and similar, dsu, graphs, matrices Solve time: 1m 39s Verified: yes Solution Problem Understanding We are given an $n \times m$ grid where each cell is a distinct chemical element. Some of these cells are already available in the laboratory. From any three elements forming three corners of an axis-aligned rectangle, the scientists can always synthesize the fourth corner....

Practice › Codeforces Solutions › Educational Codeforces Round 48 (Rated for Div. 2) ›

CF 1016F - Road Projects

CF 1016F - Road Projects Rating: 2600 Tags: dfs and similar, dp, trees Solve time: 2m 18s Verified: no Solution Problem Understanding We are given a weighted tree whose nodes are cities and whose edges are existing roads with travel times. The structure guarantees a unique simple path between any two cities, so distances are well-defined tree distances. Two special nodes matter more than all others: city 1 and city...

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Codeforces Round 503 (by SIS, Div. 2)

Codeforces Round 503 (by SIS, Div. 2) Div. 2 | 2 problems | 2/2 verified | Difficulty 1000-1000 | 4m 30s # Problem Rating Tags Accepted Time ✓ A New Building for SIS 1000 math 9,453 3m ✓ B Badge 1000 brute-force, dfs-and-similar, graphs 25,118 1m 30s ✓

Practice › Codeforces Solutions › Codeforces Round 503 (by SIS, Div. 2) ›

CF 1020B - Badge

CF 1020B - Badge Rating: 1000 Tags: brute force, dfs and similar, graphs Solve time: 1m 30s Verified: yes Solution Problem Understanding We are given a directed structure over students where each student points to exactly one other student. This forms a functional graph: every node has outdegree one, so starting from any node and repeatedly following pointers eventually forces us into a cycle. A teacher starts at some student...

Practice › Codeforces Solutions › Codeforces Round 504 (rated, Div. 1 + Div. 2, based on VK Cup 2018 Final) ›

CF 1023F - Mobile Phone Network

CF 1023F - Mobile Phone Network Rating: 2600 Tags: dfs and similar, dsu, graphs, trees Solve time: 2m 53s Verified: no Solution Problem Understanding We are given a connected graph with two types of edges. One set is already fixed by a competitor, each with a known cost. The second set is ours: these edges form a forest, and we are allowed to assign any integer weights to them. After...

Practice › Codeforces Solutions › Educational Codeforces Round 49 (Rated for Div. 2) ›

CF 1027F - Session in BSU

CF 1027F - Session in BSU Rating: 2400 Tags: binary search, dfs and similar, dsu, graph matchings, graphs Solve time: 6m 57s Verified: no Solution Problem Understanding We are given a collection of tasks, each task representing an exam that must be scheduled on exactly one of two possible days. For exam $i$, there are two candidate days $a_i$ and $b_i$, and we must choose one of them. The constraint...

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Educational Codeforces Round 49 (Rated for Div. 2)

Educational Codeforces Round 49 (Rated for Div. 2) Div. 2 | 7 problems | 4/7 verified | Difficulty 1000-2600 | 35m 5s # Problem Rating Tags Accepted Time ✓ A Palindromic Twist 1000 implementation, strings 18,799 6m 17s ✓ B Numbers on the Chessboard 1200 implementation, math 8,744 3m 37s C Minimum Value Rectangle 1600 greedy 7,152 6m 46s D Mouse Hunt 1700 dfs-and-similar, graphs 8,366 3m 49s ✓ E...

Practice › Codeforces Solutions › Educational Codeforces Round 49 (Rated for Div. 2) ›

CF 1027D - Mouse Hunt

CF 1027D - Mouse Hunt Rating: 1700 Tags: dfs and similar, graphs Solve time: 3m 49s Verified: yes Solution Problem Understanding We can think of the dorm as a directed graph where each room has exactly one outgoing edge. From every room i , the mouse deterministically moves to a[i] after one second. Because every node has exactly one outgoing edge, the graph decomposes into chains that eventually enter directed...

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Lyft Level 5 Challenge 2018 - Elimination Round

Lyft Level 5 Challenge 2018 - Elimination Round Special | 6 problems | 3/6 verified | Difficulty 1000-3500 | 50m 45s # Problem Rating Tags Accepted Time ✓ A King Escape 1000 dfs-and-similar, graphs, implementation 16,031 4m 19s ✓ B Square Difference 1100 math, number-theory 11,951 4m 51s ✓ C Permutation Game 1600 brute-force, dp, games 6,216 11m 39s ✓ D Divisors 2000 interactive, math, number-theory 2,611 8m 46s F...

Practice › Codeforces Solutions › Lyft Level 5 Challenge 2018 - Elimination Round ›

CF 1033A - King Escape

CF 1033A - King Escape Rating: 1000 Tags: dfs and similar, graphs, implementation Solve time: 4m 19s Verified: yes Solution Problem Understanding We are given a square chessboard with coordinates from 1 to n in both directions. A queen is fixed at one cell, and it attacks along rows, columns, and diagonals in the usual chess sense. A king starts at one cell and wants to reach another cell, moving...

Practice › Codeforces Solutions › Educational Codeforces Round 50 (Rated for Div. 2) ›

CF 1036G - Sources and Sinks

CF 1036G - Sources and Sinks Rating: 2700 Tags: bitmasks, brute force, dfs and similar Solve time: 5m 32s Verified: yes Solution Problem Understanding We start with a directed acyclic graph. Some vertices have no incoming edges, these are called sources, and some have no outgoing edges, these are sinks. The graph is guaranteed to have the same number of sources and sinks, and this number is at most 20....

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Manthan, Codefest 18 (rated, Div. 1 + Div. 2)

Manthan, Codefest 18 (rated, Div. 1 + Div. 2) Div. 1+2 | 6 problems | 3/6 verified | Difficulty 1300-3200 | 38m 34s # Problem Rating Tags Accepted Time ✓ A Packets 1300 constructive-algorithms, greedy, math 11,828 10m 19s B Reach Median 1300 greedy 10,877 3m 15s ✓ C Equalize 1300 dp, greedy, strings 20,111 9m 29s ✓ D Valid BFS? 1700 dfs-and-similar, graphs, shortest-paths 19,089 4m 53s G A...

Practice › Codeforces Solutions › Manthan, Codefest 18 (rated, Div. 1 + Div. 2) ›

CF 1037D - Valid BFS?

CF 1037D - Valid BFS? Rating: 1700 Tags: dfs and similar, graphs, shortest paths, trees Solve time: 4m 53s Verified: no Solution Problem Understanding We are given a tree with vertices labeled from 1 to n, and a proposed ordering of all vertices. The task is to decide whether this ordering could arise from running a breadth-first search starting at vertex 1, under some valid choice of adjacency ordering. The...

Practice › Codeforces Solutions › Codeforces Round 508 (Div. 2) ›

CF 1038E - Maximum Matching

CF 1038E - Maximum Matching Rating: 2400 Tags: bitmasks, brute force, dfs and similar, dp, graphs Solve time: 4m 42s Verified: yes Solution Problem Understanding Each block can be viewed as a weighted undirected edge between two colors, where each endpoint is one of two possible colors depending on orientation. Choosing an orientation is equivalent to deciding a direction for that edge in a path, because once we fix an...

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Codeforces Round 660 (Div. 2)

Codeforces Round 660 (Div. 2) Div. 2 | 5 problems | 3/5 verified | Difficulty 800-2700 | 13m 36s # Problem Rating Tags Accepted Time ✓ A Captain Flint and Crew Recruitment 800 brute-force, greedy, math 25,953 4m 57s B Captain Flint and a Long Voyage 1000 greedy, math 22,819 2m 12s ✓ C C 1800 dfs and similar, greedy, math 10,413 2m 35s ✓ D Captain Flint and Treasure...

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Baltic Olympiad in Informatics 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated)

Baltic Olympiad in Informatics 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated) ICPC/IOI | 4 problems | 1/4 verified | Difficulty 2100-2900 | 17m 38s # Problem Rating Tags Accepted Time ✓ A Graph 2100 *special, binary-search, dfs-and-similar 905 6m 59s B1 Village (Minimum) 2100 *special, dp, greedy 1,890 1m 47s ✓ B2 Village (Maximum) 2500 *special, dfs-and-similar, trees 1,276 7m 9s C Viruses 2900 *special, dp, shortest-paths 204 1m...

Practice › Codeforces Solutions › Codeforces Round 507 (Div. 1, based on Olympiad of Metropolises) ›

CF 1039C - Network Safety

CF 1039C - Network Safety Rating: 2200 Tags: dfs and similar, dsu, graphs, math, sortings Solve time: 8m 24s Verified: yes Solution Problem Understanding We are given a network of servers where each server has an integer label (an encryption key) in a fixed bit range. Some pairs of servers are connected, and a connection is considered safe only if the two endpoints currently hold different values. A virus is...

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Lyft Level 5 Challenge 2018 - Final Round

Lyft Level 5 Challenge 2018 - Final Round Special | 6 problems | 1/6 verified | Difficulty 1700-3100 | 30m 21s # Problem Rating Tags Accepted Time ✓ A The Tower is Going Home 1700 binary-search, two-pointers 3,076 10m 12s B Intersecting Subtrees 1900 dfs-and-similar, interactive, trees 1,708 1m 59s ✓ C Optimal Polygon Perimeter 2100 dp, geometry 1,409 5m 59s D Deduction Queries 2400 data-structures, dsu 1,186 7m E...

Practice › Codeforces Solutions › Lyft Level 5 Challenge 2018 - Final Round ›

CF 1044B - Intersecting Subtrees

CF 1044B - Intersecting Subtrees Rating: 1900 Tags: dfs and similar, interactive, trees Solve time: 1m 59s Verified: yes Solution Problem Understanding We are given a tree with n vertices, but there is a twist: there are two different labelings of the same underlying tree. In your view, the vertices are numbered from 1 to n and the edges are given in this numbering. Li Chen has independently assigned his...

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Bubble Cup 11 - Finals [Online Mirror, Div. 1]

Bubble Cup 11 - Finals [Online Mirror, Div. 1] Div. 1 | 5 problems | 4/5 verified | Difficulty 2200-3400 | 21m 12s # Problem Rating Tags Accepted Time ✓ A Last chance 2500 data-structures, flows, graph-matchings 574 4m 32s C Hyperspace Highways 2300 dfs-and-similar, graphs, trees 827 3m 39s ✓ F Shady Lady 3400 geometry, math 114 3m 49s ✓ G AI robots 2200 data-structures 1,984 2m 33s ✓...

Practice › Codeforces Solutions › Bubble Cup 11 - Finals [Online Mirror, Div. 1] ›

CF 1045C - Hyperspace Highways

CF 1045C - Hyperspace Highways Rating: 2300 Tags: dfs and similar, graphs, trees Solve time: 3m 39s Verified: yes Solution Problem Understanding We are given a connected undirected graph with up to one hundred thousand vertices and up to half a million edges. Each query asks for the shortest path length between two given vertices, measured in number of edges. A crucial extra constraint changes the structure of the graph....

Practice › Codeforces Solutions › Codeforces Round 739 (Div. 3) ›

CF 1560F2 - Nearest Beautiful Number (hard version)

CF 1560F2 - Nearest Beautiful Number (hard version) Rating: 2100 Tags: bitmasks, brute force, constructive algorithms, dfs and similar, dp, greedy Solve time: 1m 43s Verified: no Solution Problem Understanding We are asked to construct, for each query, the smallest integer that is at least a given number n , under a digit-restriction constraint. The constraint is that the resulting number may use at most k distinct decimal digits in...

Practice › Codeforces Solutions › Codeforces Round 738 (Div. 2) ›

CF 1559D2 - Mocha and Diana (Hard Version)

CF 1559D2 - Mocha and Diana (Hard Version) Rating: 2500 Tags: brute force, constructive algorithms, dfs and similar, dsu, graphs, greedy, trees, two pointers Solve time: 1m 34s Verified: yes Solution Problem Understanding We are given two different forests built on the same set of vertices from 1 to n. Each forest is already acyclic, but they may have multiple connected components. The task is to add as many new...

Practice › Codeforces Solutions › Harbour.Space Scholarship Contest 2021-2022 (open for everyone, rated, Div. 1 + Div. 2) ›

CF 1553E - Permutation Shift

CF 1553E - Permutation Shift Rating: 2100 Tags: brute force, combinatorics, constructive algorithms, dfs and similar, dsu, graphs, math Solve time: 4m 48s Verified: yes Solution Problem Understanding We start from the identity permutation, which is simply the numbers from 1 to n in order. Someone first rotates this array cyclically to the right by an unknown shift k, and then performs at most m arbitrary swaps of elements. After...

Practice › Codeforces Solutions › Codeforces Round 660 (Div. 2) ›

CF 1388D - Captain Flint and Treasure

CF 1388D - Captain Flint and Treasure Rating: 2000 Tags: data structures, dfs and similar, graphs, greedy, implementation, trees Solve time: 2m 14s Verified: yes Solution Problem Understanding We are given a directed structure over indices from 1 to n, where each index i has a value a[i] and a pointer b[i]. The pointer either leads to another index or is absent (represented by -1). The crucial operation is that...

Practice › Codeforces Solutions › Baltic Olympiad in Informatics 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated) ›

CF 1387B2 - Village (Maximum)

CF 1387B2 - Village (Maximum) Rating: 2500 Tags: *special, dfs and similar, trees Solve time: 7m 9s Verified: no Solution Problem Understanding The village is a tree where each house is a node and each road is an edge of length one. Initially, every house has exactly one villager. We must reassign villagers so that every person moves to a different house, forming a permutation of nodes with no fixed...

Practice › Codeforces Solutions › Baltic Olympiad in Informatics 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated) ›

CF 1387A - Graph

CF 1387A - Graph Rating: 2100 Tags: *special, binary search, dfs and similar, dp, math, ternary search Solve time: 6m 59s Verified: no Solution Problem Understanding We are given an undirected graph where every edge enforces a linear constraint between its endpoints. Each vertex must be assigned a real value, and every edge says exactly what the sum of its two endpoint values must be. Black edges force a sum...

Practice › Codeforces Solutions › Codeforces Round 657 (Div. 2) ›

CF 1379C - Choosing flowers

CF 1379C - Choosing flowers Rating: 2000 Tags: binary search, brute force, data structures, dfs and similar, dp, greedy, sortings, two pointers Solve time: 6m 47s Verified: no Solution Problem Understanding We are choosing exactly $n$ flowers from $m$ available types, where each type can be used an unlimited number of times. The value of picking flowers is not linear per flower, instead each type behaves like a diminishing reward...

Practice › Codeforces Solutions › Codeforces Round 651 (Div. 2) ›

CF 1370F2 - The Hidden Pair (Hard Version)

CF 1370F2 - The Hidden Pair (Hard Version) Rating: 2700 Tags: binary search, dfs and similar, graphs, interactive, shortest paths, trees Solve time: 8m 8s Verified: no Solution Problem Understanding We are given a tree and two hidden distinct nodes inside it. We do not know which nodes they are, but we can interactively probe the tree by choosing any subset of nodes. For each subset, the system returns one...

Practice › Codeforces Solutions › Codeforces Round 652 (Div. 2) ›

CF 1369F - BareLee

CF 1369F - BareLee Rating: 2700 Tags: dfs and similar, dp, games Solve time: 3m 19s Verified: yes Solution Problem Understanding Each round is a two-player deterministic game played on a single integer. A round starts with a value $s_i$ on a board and a limit $e_i$. Players alternate turns, and on each turn the current value $a$ must be replaced by either $a+1$ or $2a$. If a player ever...

Practice › Codeforces Solutions › Codeforces Round 646 (Div. 2) ›

CF 1363E - Tree Shuffling

CF 1363E - Tree Shuffling Rating: 2000 Tags: dfs and similar, dp, greedy, trees Solve time: 3m 57s Verified: no Solution Problem Understanding We are given a rooted tree where each node carries two bits of information: an initial binary digit and a desired final binary digit. The task is to transform the initial configuration into the target configuration using a special operation that allows us to take any subtree,...

Practice › Codeforces Solutions › Codeforces Round 647 (Div. 1) - Thanks, Algo Muse! ›

CF 1361C - Johnny and Megan's Necklace

CF 1361C - Johnny and Megan's Necklace Rating: 2500 Tags: binary search, bitmasks, constructive algorithms, dfs and similar, dsu, graphs Solve time: 6m 34s Verified: no Solution Problem Understanding Each input item is a small “edge gadget” consisting of two pearls, and each pearl has an integer color in the range $[0, 2^{20})$. The goal is to take all these $n$ gadgets and connect their endpoints into one single cycle...

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Codeforces Round 640 (Div. 4)

Codeforces Round 640 (Div. 4) Div. 4 | 3 problems | 0/3 verified | Difficulty 800-1500 | 29m 36s # Problem Rating Tags Accepted Time ✓ A Sum of Round Numbers 800 implementation, math 104,056 6m 16s B Same Parity Summands 1200 constructive-algorithms, math 44,806 6m 28s F Binary String Reconstruction 1500 constructive-algorithms, dfs-and-similar, math 19,400 16m 52s

Practice › Codeforces Solutions › Codeforces Round 639 (Div. 1) ›

CF 1344C - Quantifier Question

CF 1344C - Quantifier Question Rating: 2600 Tags: dfs and similar, dp, graphs, math Solve time: 3m 29s Verified: no Solution Problem Understanding We are given a directed graph on variables $x_1, x_2, \dots, x_n$. Each constraint $x_j < x_k$ behaves like an edge $j \to k$, and a full assignment of real values satisfies the formula only if every edge points from a smaller value to a larger value....

Practice › Codeforces Solutions › Codeforces Round 637 (Div. 1) - Thanks, Ivan Belonogov! ›

CF 1340C - Nastya and Unexpected Guest

CF 1340C - Nastya and Unexpected Guest Rating: 2400 Tags: dfs and similar, dp, graphs, shortest paths Solve time: 5m 29s Verified: no Solution Problem Understanding We are given a straight road modeled as integer points from 0 to n. Some of these points are special positions called safety islands, including both endpoints. Denis starts at 0 at time zero and wants to reach n as fast as possible. Time...

Practice › Codeforces Solutions › Codeforces Round 633 (Div. 1) ›

CF 1338D - Nested Rubber Bands

CF 1338D - Nested Rubber Bands Rating: 2700 Tags: constructive algorithms, dfs and similar, dp, math, trees Solve time: 6m 25s Verified: yes Solution Problem Understanding We are given a tree, and the problem asks us to think about a geometric construction that can be performed on it. Each vertex becomes a closed non-self-intersecting curve on a plane. These curves are required to interact in a very rigid way: two...

Practice › Codeforces Solutions › Codeforces Round 634 (Div. 3) ›

CF 1335F - Robots on a Grid

CF 1335F - Robots on a Grid Rating: 2200 Tags: data structures, dfs and similar, dsu, graphs, greedy, matrices Solve time: 1m 11s Verified: no Solution Problem Understanding Each cell in the grid behaves like a deterministic state in a directed graph. From every cell, there is exactly one outgoing edge pointing to one of its four neighbors, as dictated by the arrow in that cell. Because of the boundary...

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Codeforces Round 628 (Div. 2)

Codeforces Round 628 (Div. 2) Div. 2 | 3 problems | 2/3 verified | Difficulty 800-2600 | 12m 30s # Problem Rating Tags Accepted Time ✓ B CopyCopyCopyCopyCopy 800 greedy, implementation 38,820 3m 14s ✓ C Ehab and Path-etic MEXs 1500 constructive-algorithms, dfs-and-similar, greedy 17,153 1m 7s E Ehab's REAL Number Theory Problem 2600 brute-force, dfs-and-similar, graphs 2,335 8m 9s ✓

Practice › Codeforces Solutions › Codeforces Round 628 (Div. 2) ›

CF 1325E - Ehab's REAL Number Theory Problem

CF 1325E - Ehab's REAL Number Theory Problem Rating: 2600 Tags: brute force, dfs and similar, graphs, number theory, shortest paths Solve time: 8m 9s Verified: yes Solution Problem Understanding We are given a sequence of integers, and we want to select a subsequence whose product becomes a perfect square. Among all such subsequences, we need the minimum possible length. A product is a perfect square exactly when every prime...

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Codeforces Round 625 (Div. 1, based on Technocup 2020 Final Round)

Codeforces Round 625 (Div. 1, based on Technocup 2020 Final Round) Div. 1 | 3 problems | 1/3 verified | Difficulty 1700-2500 | 10m 5s # Problem Rating Tags Accepted Time ✓ B Navigation System 1700 dfs-and-similar, graphs, shortest-paths 6,437 2m 48s ✓ C World of Darkraft: Battle for Azathoth 2000 brute-force, data-structures, sortings 3,426 2m 48s D Reachable Strings 2500 data-structures, hashing, strings 1,692 4m 29s

Practice › Codeforces Solutions › Codeforces Round 625 (Div. 1, based on Technocup 2020 Final Round) ›

CF 1320B - Navigation System

CF 1320B - Navigation System Rating: 1700 Tags: dfs and similar, graphs, shortest paths Solve time: 2m 48s Verified: yes Solution Problem Understanding We are given a directed graph where intersections are nodes and roads are one-way edges. We also know a fixed simple route Polycarp actually drives from his home to his work. This route is valid in the sense that every consecutive pair of intersections is connected by...

Practice › Codeforces Solutions › Codeforces Round 621 (Div. 1 + Div. 2) ›

CF 1307D - Cow and Fields

CF 1307D - Cow and Fields Rating: 1900 Tags: binary search, data structures, dfs and similar, graphs, greedy, shortest paths, sortings Solve time: 1m 16s Verified: yes Solution Problem Understanding We are given an undirected, connected graph representing fields connected by roads. A traveler starts at node 1 and wants to reach node n using the shortest possible route. On top of the existing network, we are allowed to add...

Practice › Codeforces Solutions › Ozon Tech Challenge 2020 (Div.1 + Div.2, Rated, T-shirts + prizes!) ›

CF 1305D - Kuroni and the Celebration

CF 1305D - Kuroni and the Celebration Rating: 1900 Tags: constructive algorithms, dfs and similar, interactive, trees Solve time: 3m 8s Verified: no Solution Problem Understanding We are given a fixed tree with up to 1000 vertices. Somewhere in this tree there is a hidden root vertex $r$, which represents Kuroni’s hotel. The structure of the tree is known, but the root is not. The only way to extract information...

Practice › Codeforces Solutions › Educational Codeforces Round 82 (Rated for Div. 2) ›

CF 1303C - Perfect Keyboard

CF 1303C - Perfect Keyboard Rating: 1600 Tags: dfs and similar, greedy, implementation Solve time: 2m 41s Verified: no Solution Problem Understanding We are given a string consisting of lowercase letters, and we want to decide whether it is possible to arrange all 26 letters of the alphabet in a single line such that every consecutive pair of characters appearing in the string are also adjacent in this line layout....

Practice › Codeforces Solutions › Kotlin Heroes: Episode 3 ›

CF 1297E - Modernization of Treeland

CF 1297E - Modernization of Treeland Rating: - Tags: *special, dfs and similar, trees Solve time: 3m 35s Verified: no Solution Problem Understanding We are given a tree of cities. From this tree we must choose a subset of cities $S$ such that two conditions hold simultaneously. First, if we only look at edges whose endpoints are both in $S$, the chosen vertices must remain connected, so $S$ forms a...

Practice › Codeforces Solutions › Codeforces Round 617 (Div. 3) ›

CF 1296F - Berland Beauty

CF 1296F - Berland Beauty Rating: 2100 Tags: constructive algorithms, dfs and similar, greedy, sortings, trees Solve time: 7m 17s Verified: no Solution Problem Understanding We are given a connected network of $n$ stations connected by $n-1$ railway segments, which means the structure is a tree. Each edge in this tree has an unknown integer weight in the range from 1 to $10^6$. We are also given several observations from...

Practice › Codeforces Solutions › Codeforces Round 615 (Div. 3) ›

CF 1294F - Three Paths on a Tree

CF 1294F - Three Paths on a Tree Rating: 2000 Tags: dfs and similar, dp, greedy, trees Solve time: 4m 58s Verified: no Solution Problem Understanding We are working with a tree, which means there is exactly one simple path between any two vertices. From this tree we must choose three distinct vertices, call them $a$, $b$, and $c$. Once these three points are fixed, we look at the three...

Practice › Codeforces Solutions › Codeforces Round 614 (Div. 1) ›

CF 1292C - Xenon's Attack on the Gangs

CF 1292C - Xenon's Attack on the Gangs Rating: 2300 Tags: combinatorics, dfs and similar, dp, greedy, trees Solve time: 1m 10s Verified: no Solution Problem Understanding We are given a tree with $n$ nodes and $n-1$ edges. Each edge is assigned a distinct label from $0$ to $n-2$, so every label appears exactly once. For any pair of nodes $u, v$, we look at the unique path between them...

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Codeforces Round 616 (Div. 1)

Codeforces Round 616 (Div. 1) Div. 1 | 5 problems | 1/5 verified | Difficulty 1600-3500 | 19m 56s # Problem Rating Tags Accepted Time ✓ A Mind Control 1600 brute-force, data-structures, implementation 8,899 5m 40s C Prefix Enlightenment 2400 dfs-and-similar, dsu, graphs 2,012 1m 56s ✓ D Coffee Varieties (hard version) 3000 constructive-algorithms, graphs, interactive 948 3m 41s E Cartesian Tree 3300 data-structures 670 4m 7s F Making Shapes...

Practice › Codeforces Solutions › Codeforces Round 612 (Div. 1) ›

CF 1286B - Numbers on Tree

CF 1286B - Numbers on Tree Rating: 1800 Tags: constructive algorithms, data structures, dfs and similar, graphs, greedy, trees Solve time: 5m 21s Verified: no Solution Problem Understanding We are given a rooted tree where every node has a hidden integer value. What we do know is the tree structure and, for each node, a number c_i . This number tells us something local to the subtree: among all nodes...

Practice › Codeforces Solutions › Codeforces Round 613 (Div. 2) ›

CF 1285D - Dr. Evil Underscores

CF 1285D - Dr. Evil Underscores Rating: 1900 Tags: bitmasks, brute force, dfs and similar, divide and conquer, dp, greedy, strings, trees Solve time: 8m 56s Verified: yes Solution Problem Understanding We are given a list of integers, and we are allowed to choose a single integer $X$. Once $X$ is fixed, every array value is transformed by XOR with $X$, and we care about the largest transformed value. The...

Practice › Codeforces Solutions › Codeforces Round 610 (Div. 2) ›

CF 1282E - The Cake Is a Lie

CF 1282E - The Cake Is a Lie Rating: 2400 Tags: constructive algorithms, data structures, dfs and similar, graphs Solve time: 5m 36s Verified: no Solution Problem Understanding We are given a collection of triangles that once formed a triangulation of a convex polygon with $n$ vertices. Each triangle corresponds to one cut made during a process where we repeatedly remove a boundary triangle from a convex polygon until nothing...

Practice › Codeforces Solutions › Codeforces Round 607 (Div. 1) ›

CF 1280C - Jeremy Bearimy

CF 1280C - Jeremy Bearimy Rating: 2000 Tags: dfs and similar, graphs, greedy, trees Solve time: 11m 16s Verified: no Solution Problem Understanding We are given a weighted tree with $2k$ vertices. On these vertices we must place $2k$ people, where the people are grouped into $k$ fixed pairs. After the placement, each pair contributes the distance between the two vertices they occupy, measured along the unique path in the...

Practice › Codeforces Solutions › Educational Codeforces Round 78 (Rated for Div. 2) ›

CF 1278E - Tests for problem D

CF 1278E - Tests for problem D Rating: 2200 Tags: constructive algorithms, dfs and similar, divide and conquer, trees Solve time: 10m 37s Verified: no Solution Problem Understanding We are given a tree with n labeled vertices. The task is not to manipulate the tree directly, but to construct a completely different object: n line segments on the number line, using the integers from 1 to 2n exactly once as...

Practice › Codeforces Solutions ›

Codeforces Round 606 (Div. 1, based on Technocup 2020 Elimination Round 4)

Codeforces Round 606 (Div. 1, based on Technocup 2020 Elimination Round 4) Div. 1 | 4 problems | 2/4 verified | Difficulty 1400-3400 | 21m 23s # Problem Rating Tags Accepted Time ✓ A As Simple as One and Two 1400 dp, greedy 12,947 5m 49s B Two Fairs 1900 combinatorics, dfs-and-similar, dsu 5,668 1m 34s ✓ C Beautiful Rectangle 2300 brute-force, combinatorics, constructive-algorithms 1,788 11m 51s F Asterisk Substrings...

Practice › Codeforces Solutions › Good Bye 2019 ›

CF 1270G - Subset with Zero Sum

CF 1270G - Subset with Zero Sum Rating: 2700 Tags: constructive algorithms, dfs and similar, graphs, math Solve time: 5m 39s Verified: no Solution Problem Understanding We are given an array of integers where each position i has a value a[i] constrained in a tight interval that depends on its index. The i-th element is never too negative and never too large: it always lies between i − n and...

Practice › Codeforces Solutions › Codeforces Round 601 (Div. 1) ›

CF 1254E - Send Tree to Charlie

CF 1254E - Send Tree to Charlie Rating: 3300 Tags: combinatorics, dfs and similar, dsu, trees Solve time: 4m 42s Verified: yes Solution Problem Understanding We are given a tree with $n$ nodes, where each node initially holds a unique label from $1$ to $n$. Someone then performs a process that is equivalent to choosing an ordering of all edges and, for each edge in that order, swapping the labels...

Practice › Codeforces Solutions › Codeforces Round 600 (Div. 2) ›

CF 1253D - Harmonious Graph

CF 1253D - Harmonious Graph Rating: 1700 Tags: constructive algorithms, dfs and similar, dsu, graphs, greedy, sortings Solve time: 1m 43s Verified: yes Solution Problem Understanding We are given an undirected graph on vertices labeled from 1 to n, and we are allowed to add edges. The goal is to make the graph satisfy a very specific reachability constraint that depends on the natural ordering of vertices. The condition says...

Practice › Codeforces Solutions › Codeforces Round 595 (Div. 3) ›

CF 1249B2 - Books Exchange (hard version)

CF 1249B2 - Books Exchange (hard version) Rating: 1300 Tags: dfs and similar, dsu, math Solve time: 4m 6s Verified: no Solution Problem Understanding We are given a system where each child initially holds a unique book, and every day each book is passed to another fixed child according to a permutation. After one day, every book moves once; after two days, it moves again under the same rule, and...

Practice › Codeforces Solutions › Codeforces Round 599 (Div. 1) ›

CF 1242B - 0-1 MST

CF 1242B - 0-1 MST Rating: 1900 Tags: dfs and similar, dsu, graphs, sortings Solve time: 5m 48s Verified: yes Solution Problem Understanding We are given a complete undirected graph on $n$ vertices. Every pair of vertices is connected, but edges come in only two possible weights: either 0 or 1. Among all $\binom{n}{2}$ edges, exactly $m$ of them have weight 1, and every other edge implicitly has weight 0....

Practice › Codeforces Solutions › Codeforces Round 594 (Div. 1) ›

CF 1239D - Catowice City

CF 1239D - Catowice City Rating: 2400 Tags: 2-sat, dfs and similar, graph matchings, graphs Solve time: 5m 40s Verified: no Solution Problem Understanding We are given a system of $n$ people, each of whom owns exactly one cat, forming a natural pairing between person $i$ and cat $i$. Alongside this structure, there is an undirected bipartite relationship between people and cats: each input edge connects a resident $a$ with...

Practice › Codeforces Solutions › Codeforces Round 593 (Div. 2) ›

CF 1236F - Alice and the Cactus

CF 1236F - Alice and the Cactus Rating: 3000 Tags: dfs and similar, graphs, math, probabilities Solve time: 5m 7s Verified: no Solution Problem Understanding We are given a connected undirected graph with a special structure: it is a cactus, meaning every edge belongs to at most one simple cycle. On this graph, each vertex independently survives with probability $1/2$, otherwise it is deleted together with all incident edges. After...

Practice › Codeforces Solutions › Codeforces Round 586 (Div. 1 + Div. 2) ›

CF 1220E - Tourism

CF 1220E - Tourism Rating: 2200 Tags: dfs and similar, dp, dsu, graphs, greedy, trees Solve time: 3m 3s Verified: yes Solution Problem Understanding We are given a connected undirected graph where each vertex represents a city and each city has a fixed value. Alex starts from a specific city and walks through the graph by traversing edges, with one restriction: he is not allowed to immediately traverse back along...

Practice › Codeforces Solutions › Bubble Cup 12 - Finals [Online Mirror, unrated, Div. 1] ›

CF 1218I - The Light Square

CF 1218I - The Light Square Rating: 2100 Tags: 2-sat, dfs and similar, greedy Solve time: 2m 35s Verified: yes Solution Problem Understanding We are given three ingredients that define a transformation problem on a binary grid. First is an initial $N \times N$ board of lights, each cell either on or off. Second is a target $N \times N$ configuration we want to reach. Third is a fixed binary...

Practice › Codeforces Solutions › Educational Codeforces Round 72 (Rated for Div. 2) ›

CF 1217D - Coloring Edges

CF 1217D - Coloring Edges Rating: 2100 Tags: constructive algorithms, dfs and similar, graphs Solve time: 2m 41s Verified: yes Solution Problem Understanding We are given a directed graph where each edge is fixed in advance, and we must assign a color (an integer label) to every edge. The constraint is not about vertices but about directed cycles: if you look at all edges of a single color, they must...

Practice › Codeforces Solutions › Codeforces Round 583 (Div. 1 + Div. 2, based on Olympiad of Metropolises) ›

CF 1214H - Tiles Placement

CF 1214H - Tiles Placement Rating: 2800 Tags: constructive algorithms, dfs and similar, trees Solve time: 5m 42s Verified: no Solution Problem Understanding We are given a tree with $n$ vertices, where each vertex represents a square in a pedestrian network. Each vertex must be assigned one of $k$ colors. The requirement is global and path-based: if you take any simple path in the tree that contains exactly $k$ vertices,...

Practice › Codeforces Solutions › Codeforces Round 583 (Div. 1 + Div. 2, based on Olympiad of Metropolises) ›

CF 1214D - Treasure Island

CF 1214D - Treasure Island Rating: 1900 Tags: dfs and similar, dp, flows, hashing Solve time: 3m 29s Verified: yes Solution Problem Understanding We are given an $n \times m$ grid that represents a map. Each cell is either blocked or free. We start at the top-left cell $(1,1)$ and want to reach the bottom-right cell $(n,m)$. Movement is highly restricted: from any cell we can only go either one...

Practice › Codeforces Solutions › Codeforces Round 582 (Div. 3) ›

CF 1213F - Unstable String Sort

CF 1213F - Unstable String Sort Rating: 2100 Tags: data structures, dfs and similar, dsu, graphs, greedy, implementation, strings Solve time: 5m 5s Verified: yes Solution Problem Understanding We are given two permutations of the indices of a string, and both permutations describe an ordering in which the hidden string must appear sorted. In other words, if we take the string and read characters in the order dictated by permutation...

Practice › Codeforces Solutions › Codeforces Round 584 - Dasha Code Championship - Elimination Round (rated, open for everyone, Div. 1 + Div. 2) ›

CF 1209F - Koala and Notebook

CF 1209F - Koala and Notebook Rating: 2600 Tags: data structures, dfs and similar, graphs, shortest paths, strings, trees Solve time: 4m 29s Verified: no Solution Problem Understanding We are given an undirected connected graph with up to 100,000 cities and roads, where each road has a unique identifier from 1 to m. Koala starts at city 1 and travels through the graph. Every time he traverses a road, he...

Practice › Codeforces Solutions › Codeforces Round 584 - Dasha Code Championship - Elimination Round (rated, open for everyone, Div. 1 + Div. 2) ›

CF 1209D - Cow and Snacks

CF 1209D - Cow and Snacks Rating: 1700 Tags: dfs and similar, dsu, graphs Solve time: 2m 49s Verified: yes Solution Problem Understanding We are given a collection of snack types and a group of guests. Each snack type appears exactly once, so there are $n$ distinct items labeled $1$ to $n$. Each guest has two preferred snack types. Guests arrive in some chosen order, and when a guest arrives,...

Practice › Codeforces Solutions › Manthan, Codefest 19 (open for everyone, rated, Div. 1 + Div. 2) ›

CF 1208F - Bits And Pieces

CF 1208F - Bits And Pieces Rating: 2600 Tags: bitmasks, dfs and similar, dp, greedy Solve time: 2m 39s Verified: yes Solution Problem Understanding We are given a sequence of integers and asked to choose three indices $i < j < k$. For each such triple, we take the value of the first element OR the bitwise AND of the other two elements. The goal is to maximize this expression...

Practice › Codeforces Solutions › Educational Codeforces Round 71 (Rated for Div. 2) ›

CF 1207G - Indie Album

CF 1207G - Indie Album Rating: 2700 Tags: data structures, dfs and similar, hashing, string suffix structures, strings, trees Solve time: 4m 10s Verified: no Solution Problem Understanding We are given a growing collection of strings, where each new string is either a single character or an old string extended by exactly one character at the end. This means the entire system forms a rooted tree: every string points to...

Practice › Codeforces Solutions ›

Codeforces Round 564 (Div. 1)

Codeforces Round 564 (Div. 1) Div. 1 | 7 problems | 3/7 verified | Difficulty 1800-3300 | 41m 7s # Problem Rating Tags Accepted Time ✓ A Nauuo and Cards 1800 greedy, implementation 5,175 7m 25s ✓ B Nauuo and Circle 1900 combinatorics, dfs-and-similar, dp 4,404 1m 31s ✓ C1 Nauuo and Pictures (easy version) 2300 dp, probabilities 1,225 6m 32s ✓ C2 Nauuo and Pictures (hard version) 2600 dp,...

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CF 1103C - Johnny Solving

CF 1103C - Johnny Solving Rating: 2700 Tags: constructive algorithms, dfs and similar, graphs, math Solve time: 4m 21s Verified: yes Solution Problem Understanding We are given a connected undirected simple graph where every vertex has degree at least three. Along with the graph, we are also given an integer $k$. The task is not to compute a single structure, but to decide between two fundamentally different constructions. One option...

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CF 1100E - Andrew and Taxi

CF 1100E - Andrew and Taxi Rating: 2200 Tags: binary search, dfs and similar, graphs Solve time: 7m 2s Verified: no Solution Problem Understanding We are given a directed graph representing a city map, where each road has a direction and a cost associated with reversing it. The mayor’s goal is to modify the directions of some roads so that the final directed graph contains no directed cycle in the...

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Codeforces Round 530 (Div. 2)

Codeforces Round 530 (Div. 2) Div. 2 | 4 problems | 2/4 verified | Difficulty 800-2400 | 24m 24s # Problem Rating Tags Accepted Time ✓ A Snowball 800 implementation 13,348 6m 22s ✓ B Squares and Segments 1100 binary-search, constructive-algorithms, math 11,476 1m 10s ✓ C Postcard 1200 constructive-algorithms, implementation 10,420 10m 9s F Cookies 2400 binary-search, data-structures, dfs-and-similar 1,036 6m 43s

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CF 1099F - Cookies

CF 1099F - Cookies Rating: 2400 Tags: binary search, data structures, dfs and similar, dp, games, trees Solve time: 6m 43s Verified: no Solution Problem Understanding We are given a rooted tree where each vertex contains a pile of cookies. Every vertex also has a cost for eating one cookie at that vertex, and every edge from a node to its parent has a cost for moving upward along it....

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Codeforces Round 530 (Div. 1)

Codeforces Round 530 (Div. 1) Div. 1 | 6 problems | 3/6 verified | Difficulty 1600-3500 | 37m 57s # Problem Rating Tags Accepted Time ✓ A Sum in the tree 1600 constructive-algorithms, dfs-and-similar, greedy 9,547 9m 13s B Nice table 2100 brute-force, constructive-algorithms, greedy 1,797 5m 15s ✓ C Construct a tree 2400 binary-search, constructive-algorithms, dfs-and-similar 1,161 5m 19s ✓ D Eels 2800 data-structures 882 4m 20s ✓ E...

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CF 1098A - Sum in the tree

CF 1098A - Sum in the tree Rating: 1600 Tags: constructive algorithms, dfs and similar, greedy, trees Solve time: 9m 13s Verified: no Solution Problem Understanding We are given a rooted tree where vertex 1 is the root. Every vertex originally had a non-negative integer value written on it, but those values are now lost. What remains is partial information about prefix sums along root paths. For any vertex $v$,...

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CF 1098C - Construct a tree

CF 1098C - Construct a tree Rating: 2400 Tags: binary search, constructive algorithms, dfs and similar, graphs, greedy, trees Solve time: 5m 19s Verified: yes Solution Problem Understanding We are asked to build a rooted tree on vertices labeled from 1 to n, where vertex 1 is fixed as the root. Each node except the root has exactly one parent, so the structure is fully determined by the parent array....

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Educational Codeforces Round 56 (Rated for Div. 2)

Educational Codeforces Round 56 (Rated for Div. 2) Div. 2 | 7 problems | 4/7 verified | Difficulty 800-2400 | 38m 7s # Problem Rating Tags Accepted Time ✓ A Dice Rolling 800 math 18,356 6m 28s B Letters Rearranging 900 constructive-algorithms, greedy, sortings 17,700 6m 33s C Mishka and the Last Exam 1300 greedy 9,719 9m 12s D Beautiful Graph 1700 dfs-and-similar, graphs 11,323 3m 33s ✓ E Intersection...

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CF 1073F - Choosing Two Paths

CF 1073F - Choosing Two Paths Rating: 2500 Tags: dfs and similar, dp, greedy, trees Solve time: 5m 52s Verified: no Solution Problem Understanding We are given a tree, meaning a connected graph with no cycles. On this tree we must pick two simple paths, each defined by choosing two endpoints. The endpoints of the two paths must all be distinct, and neither path is allowed to contain either endpoint...

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Codeforces Round 518 (Div. 1) [Thanks, Mail.Ru!]

Codeforces Round 518 (Div. 1) [Thanks, Mail.Ru!] Div. 1 | 5 problems | 0/5 verified | Difficulty 1800-3100 | 37m 58s # Problem Rating Tags Accepted Time ✓ A Array Without Local Maximums 1900 dp 3,132 6m 9s B Multihedgehog 1800 dfs-and-similar, graphs, shortest-paths 2,860 9m 7s C Knights 2600 constructive-algorithms 714 8m 40s D Computer Game 3100 dp, greedy, math 491 5m 2s E Random Forest Rank 2800 dp,...

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CF 1067B - Multihedgehog

CF 1067B - Multihedgehog Rating: 1800 Tags: dfs and similar, graphs, shortest paths Solve time: 9m 7s Verified: no Solution Problem Understanding We are given a tree with $n$ vertices and asked whether it can be generated by a very specific recursive construction parameterized by $k$. The construction starts from a special tree called a hedgehog, where exactly one vertex behaves as a central hub and all other vertices are...

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Mail.Ru Cup 2018 - Practice Round

Mail.Ru Cup 2018 - Practice Round Special | 3 problems | 2/3 verified | Difficulty 900-2000 | 12m 23s # Problem Rating Tags Accepted Time ✓ A Bmail Computer Network 900 *special, dfs-and-similar, trees 7,467 4m 52s ✓ B DDoS 1400 *special, brute-force 1,970 4m 25s ✓ C Tanya and Colored Candies 2000 *special, dp 1,171 3m 6s

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CF 912E - Prime Gift

CF 912E - Prime Gift Rating: 2400 Tags: binary search, dfs and similar, math, meet-in-the-middle, number theory, two pointers Solve time: 7m 30s Verified: yes Solution Problem Understanding We are asked to enumerate a very specific set of integers and then pick a particular element from that ordered list. The allowed numbers are those whose prime factors all come from a fixed small set of given primes. In other words,...

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CF 909E - Coprocessor

CF 909E - Coprocessor Rating: 1900 Tags: dfs and similar, dp, graphs, greedy Solve time: 5m 29s Verified: yes Solution Problem Understanding The program consists of tasks that must be executed in an order consistent with a dependency graph. Each task may depend on earlier tasks, forming a directed acyclic graph where execution is only allowed once all prerequisites are completed. Every task has a fixed execution location. Some tasks...

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Codeforces Round 453 (Div. 2)

Codeforces Round 453 (Div. 2) Div. 2 | 2 problems | 2/2 verified | Difficulty 1100-1200 | 9m 53s # Problem Rating Tags Accepted Time ✓ A Visiting a Friend 1100 greedy, implementation 10,275 5m 16s ✓ B Coloring a Tree 1200 dfs-and-similar, dsu, greedy 11,948 4m 37s ✓

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Codeforces Round 453 (Div. 1)

Codeforces Round 453 (Div. 1) Div. 1 | 5 problems | 3/5 verified | Difficulty 1500-3300 | 12m 51s # Problem Rating Tags Accepted Time ✓ A Hashing Trees 1500 constructive-algorithms, trees 5,377 2m 56s B GCD of Polynomials 2200 constructive-algorithms, math 1,640 2m 34s ✓ C Bipartite Segments 2300 binary-search, data-structures, dfs-and-similar 1,298 2m 44s ✓ D Weighting a Tree 2700 constructive-algorithms, dfs-and-similar, graphs 630 2m 17s E Cyclic...

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CF 901D - Weighting a Tree

CF 901D - Weighting a Tree Rating: 2700 Tags: constructive algorithms, dfs and similar, graphs Solve time: 2m 17s Verified: no Solution Problem Understanding We are given a connected undirected graph where every edge must eventually receive an integer weight. For each vertex, we are also given a target value, and the requirement is that if you look at all edges incident to a vertex and sum their weights, that...

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CF 901C - Bipartite Segments

CF 901C - Bipartite Segments Rating: 2300 Tags: binary search, data structures, dfs and similar, dsu, graphs, two pointers Solve time: 2m 44s Verified: yes Solution Problem Understanding We are given a graph whose vertices are arranged in a fixed line from 1 to n. The edges are arbitrary, but the structure is restricted so that the graph does not contain any cycle of even length when edges are treated...

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CF 1056D - Decorate Apple Tree

CF 1056D - Decorate Apple Tree Rating: 1600 Tags: constructive algorithms, dfs and similar, dp, graphs, greedy, sortings, trees Solve time: 2m 24s Verified: yes Solution Problem Understanding We are given a rooted tree, with node 1 fixed as the root. Only leaf nodes initially receive colors, and all other nodes are uncolored. A leaf, in this problem, is defined as a node whose subtree consists of only itself, which...

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CF 1057A - Bmail Computer Network

CF 1057A - Bmail Computer Network Rating: 900 Tags: *special, dfs and similar, trees Solve time: 4m 52s Verified: yes Solution Problem Understanding We are given a growing network of routers that forms a tree rooted at router 1. Every router except the first was added one by one, and each new router was directly connected to exactly one earlier router. This means every router has a single parent, and...

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CF 1060E - Sergey and Subway

CF 1060E - Sergey and Subway Rating: 2000 Tags: dfs and similar, dp, trees Solve time: 6m 55s Verified: no Solution Problem Understanding We start with a tree of subway stations. Every station is a node, and every tunnel is an edge, so there is exactly one simple path between any two stations. The quantity we care about is the total distance over all unordered pairs of stations, where distance...

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Codeforces Round 520 (Div. 2)

Codeforces Round 520 (Div. 2) Div. 2 | 6 problems | 4/6 verified | Difficulty 1300-2900 | 22m 46s # Problem Rating Tags Accepted Time ✓ A A Prank 1300 greedy, implementation 9,306 2m 47s ✓ B Math 1500 greedy, math, number-theory 9,890 7m 36s ✓ C Banh-mi 1600 greedy, implementation, math 5,950 3m 30s D Fun with Integers 1800 dfs-and-similar, graphs, implementation 4,170 2m 39s ✓ E Company 2300...

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CF 1062F - Upgrading Cities

CF 1062F - Upgrading Cities Rating: 2900 Tags: dfs and similar, graphs Solve time: 3m 52s Verified: no Solution Problem Understanding We are given a directed acyclic graph of cities connected by one-way roads. From the constraints, the graph has no directed cycles, so it behaves like a partial order: some cities are comparable through reachability, and others are incomparable. A city is called important if it behaves like a...

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CF 1062E - Company

CF 1062E - Company Rating: 2300 Tags: binary search, data structures, dfs and similar, greedy, trees Solve time: 2m 22s Verified: yes Solution Problem Understanding The company hierarchy forms a rooted tree where employee 1 is the root, and every other employee has exactly one direct boss. This defines a parent relationship and also induces depths from the root, where depth is the number of edges from employee 1. Each...

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CF 1062D - Fun with Integers

CF 1062D - Fun with Integers Rating: 1800 Tags: dfs and similar, graphs, implementation, math Solve time: 2m 39s Verified: yes Solution Problem Understanding We are given a set of integers from the range of absolute values 2 up to n, and each number also has its negative counterpart available. Think of every integer i in this range as a node in a graph, including both i and -i. A...

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Educational Codeforces Round 52 (Rated for Div. 2)

Educational Codeforces Round 52 (Rated for Div. 2) Div. 2 | 7 problems | 3/7 verified | Difficulty 800-2700 | 26m 32s # Problem Rating Tags Accepted Time ✓ A Vasya and Chocolate 800 implementation, math 15,264 3m 48s ✓ B Vasya and Isolated Vertices 1300 constructive-algorithms, graphs 11,597 5m 51s C Make It Equal 1600 greedy 8,290 2m 44s ✓ D Three Pieces 2200 dfs-and-similar, dp, shortest-paths 1,445 3m...

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CF 1065F - Up and Down the Tree

CF 1065F - Up and Down the Tree Rating: 2500 Tags: dfs and similar, dp, trees Solve time: 5m 1s Verified: no Solution Problem Understanding We are given a rooted tree with vertex 1 as the root, and every vertex except the root has exactly one parent defined by the input. Some vertices are leaves in the usual sense of the tree structure. A token starts at the root and...

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CF 1065D - Three Pieces

CF 1065D - Three Pieces Rating: 2200 Tags: dfs and similar, dp, shortest paths Solve time: 3m 34s Verified: yes Solution Problem Understanding We are given an $N \times N$ grid where every cell contains a unique number from $1$ to $N^2$. These numbers define a forced visiting order: we must start at the cell containing 1, then eventually reach the cell containing 2, then 3, and continue in increasing...

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CF 1600J - Robot Factory

CF 1600J - Robot Factory Rating: 1400 Tags: bitmasks, dfs and similar Solve time: 1m 44s Verified: yes Solution Problem Understanding The grid describes a rectangular factory floor where each cell is a tile that may have walls on some of its four sides. Each tile contains a number from 0 to 15, and this number encodes its walls using four bits. Interpreting the binary representation from most significant to...

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Codeforces Round 875 (Div. 1)

Codeforces Round 875 (Div. 1) Div. 1 | 6 problems | 3/6 verified | Difficulty 1400-3500 | 14m 54s # Problem Rating Tags Accepted Time ✓ A Copil Copac Draws Trees 1400 dfs-and-similar, dp, graphs 20,309 2m ✓ B The BOSS Can Count Pairs 2000 brute-force, math 5,850 3m 9s ✓ C Hyperregular Bracket Strings 2400 combinatorics, greedy, hashing 2,184 1m 14s D Mex Tree 2800 brute-force, dp, trees 932...

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CF 1830A - Copil Copac Draws Trees

CF 1830A - Copil Copac Draws Trees Rating: 1400 Tags: dfs and similar, dp, graphs, trees Solve time: 2m Verified: yes Solution Problem Understanding We are given a tree described by an ordered list of edges. The edges are not just connectivity information, their order matters because the drawing process scans them sequentially again and again. The process starts with only vertex 1 being considered “drawn”. In each full pass...

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Codeforces Round 869 (Div. 1)

Codeforces Round 869 (Div. 1) Div. 1 | 6 problems | 3/6 verified | Difficulty 1500-3500 | 14m 54s # Problem Rating Tags Accepted Time ✓ A Almost Increasing Subsequence 1500 binary-search, data-structures, greedy 12,754 2m 35s ✓ B Fish Graph 1900 brute-force, constructive-algorithms, dfs-and-similar 5,100 2m 40s C Similar Polynomials 2400 combinatorics, math 1,227 1m 21s ✓ D Toy Machine 2700 constructive-algorithms, games, implementation 1,034 1m 9s ✓ E...

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CF 1817B - Fish Graph

CF 1817B - Fish Graph Rating: 1900 Tags: brute force, constructive algorithms, dfs and similar, graphs Solve time: 2m 40s Verified: no Solution Problem Understanding We are given an undirected simple graph and asked whether we can select a subset of its edges that forms a very specific structure called a Fish Graph. The target structure consists of two parts. First, there must be a simple cycle. Second, exactly one...

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CF 1804E - Routing

CF 1804E - Routing Rating: 2400 Tags: bitmasks, brute force, dfs and similar, dp, graphs Solve time: 2m 51s Verified: no Solution Problem Understanding We are given an undirected, connected graph with up to 20 vertices. Each vertex represents a server, and edges represent direct bidirectional communication links. For every server $u$, we must choose exactly one adjacent vertex $a(u)$. Think of this as assigning each node a single outgoing...

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CF 1740E - Hanging Hearts

CF 1740E - Hanging Hearts Rating: 1800 Tags: constructive algorithms, data structures, dfs and similar, dp, greedy, trees Solve time: 3m 11s Verified: no Solution Problem Understanding We are given a rooted tree where each node represents a card. Card 1 is fixed as the root, and every other card hangs from exactly one earlier card, forming a structure where every node has a single parent and edges always point...

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CF 1726D - Edge Split

CF 1726D - Edge Split Rating: 2000 Tags: brute force, constructive algorithms, dfs and similar, dsu, graphs, probabilities, trees Solve time: 3m 56s Verified: no Solution Problem Understanding We are given a connected undirected graph with a small number of extra edges beyond a tree. For each edge, we must decide whether it is colored red or blue. After fixing the coloring, we look at two induced subgraphs: one formed...

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CF 1721F - Matching Reduction

CF 1721F - Matching Reduction Rating: 2800 Tags: brute force, constructive algorithms, dfs and similar, flows, graph matchings, graphs, interactive Solve time: 4m 58s Verified: no Solution Problem Understanding We are working with a bipartite graph where the left side has $n_1$ vertices and the right side has $n_2$ vertices. Edges are fixed and each edge connects one left vertex to one right vertex. At any moment, we consider a...

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Educational Codeforces Round 134 (Rated for Div. 2)

Educational Codeforces Round 134 (Rated for Div. 2) Div. 2 | 6 problems | 2/6 verified | Difficulty 800-2800 | 21m 34s # Problem Rating Tags Accepted Time ✓ A Image 800 greedy, implementation 28,308 3m 11s ✓ B Deadly Laser 1000 implementation 23,878 4m 23s C Min-Max Array Transformation 1400 binary-search, greedy, two-pointers 14,557 2m 13s ✓ D Maximum AND 1800 bitmasks, dfs-and-similar, divide-and-conquer 7,679 3m 45s E Prefix...

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CF 1721E - Prefix Function Queries

CF 1721E - Prefix Function Queries Rating: 2200 Tags: dfs and similar, dp, hashing, string suffix structures, strings, trees Solve time: 3m 4s Verified: no Solution Problem Understanding We are given a fixed reference string and then asked to process many short query strings. For each query, we temporarily append the query string to the reference, compute the prefix function on the resulting concatenation, and output only the prefix function...

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CF 1721D - Maximum AND

CF 1721D - Maximum AND Rating: 1800 Tags: bitmasks, dfs and similar, divide and conquer, greedy, sortings Solve time: 3m 45s Verified: no Solution Problem Understanding We are given two arrays of equal length. One array, call it a , is fixed in place. The second array b can be permuted arbitrarily. After choosing a permutation of b , we pair elements by index and form a new array where...

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CF 1712F - Triameter

CF 1712F - Triameter Rating: 3200 Tags: binary search, data structures, dfs and similar, trees Solve time: 3m 7s Verified: no Solution Problem Understanding We are given a tree with unit-weight edges. From this tree we identify a special set of vertices, the leaves, meaning the vertices whose degree is exactly one. For each query, we conceptually add a complete graph over these leaves, but only among pairs where the...

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CF 1656E - Equal Tree Sums

CF 1656E - Equal Tree Sums Rating: 2200 Tags: constructive algorithms, dfs and similar, math, trees Solve time: 3m 11s Verified: no Solution Problem Understanding We are given a tree, and we must assign a nonzero integer to every vertex. The constraint is not about the whole tree sum, but about what happens when a vertex is removed. If we delete any vertex $v$, the tree splits into several connected...

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CF 1654D - Potion Brewing Class

CF 1654D - Potion Brewing Class Rating: 2100 Tags: dfs and similar, math, number theory, trees Solve time: 9m 14s Verified: yes Solution Problem Understanding We are given a set of ingredients, each of which must appear in some positive integer quantity in a final mixture. The professor does not provide absolute amounts, but instead gives exactly $n-1$ constraints. Each constraint relates two ingredients and fixes their ratio: if ingredient...

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CF 1654G - Snowy Mountain

CF 1654G - Snowy Mountain Rating: 2900 Tags: data structures, dfs and similar, graphs, greedy, shortest paths, trees Solve time: 4m 24s Verified: no Solution Problem Understanding We are given a tree where some vertices are marked as “base lodges”. Every vertex inherits a height equal to its distance from the nearest lodge. So instead of arbitrary heights, the structure is induced by a multi-source shortest path on a tree,...

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CF 1646D - Weight the Tree

CF 1646D - Weight the Tree Rating: 2000 Tags: constructive algorithms, dfs and similar, dp, implementation, trees Solve time: 3m 56s Verified: yes Solution Problem Understanding We are given a tree, and we must assign a positive integer weight to every vertex. A vertex is called good if its weight equals the sum of the weights of all vertices adjacent to it. The goal is not just to satisfy this...

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CF 1593B - Make it Divisible by 25

CF 1593B - Make it Divisible by 25 Rating: 900 Tags: dfs and similar, dp, greedy, math Solve time: 2m 52s Verified: yes Solution Problem Understanding We are given a number written in decimal form, and we are allowed to delete digits one by one from anywhere in the number. After each deletion, the remaining digits close up, and any leading zeros disappear automatically. The process continues until we decide...

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CF 1583E - Moment of Bloom

CF 1583E - Moment of Bloom Rating: 2200 Tags: constructive algorithms, dfs and similar, graph matchings, graphs, greedy, trees Solve time: 6m 39s Verified: no Solution Problem Understanding We are given a connected undirected graph where every edge initially has weight 0. We then receive a sequence of queries, each query specifying two vertices. For each query, we must choose a simple path between its endpoints and add 1 to...

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CF 1578J - Just Kingdom

CF 1578J - Just Kingdom Rating: 3100 Tags: brute force, data structures, dfs and similar Solve time: 5m 32s Verified: no Solution Problem Understanding We are given a rooted hierarchy with a single root, the king, and up to $n$ lords forming a tree where each lord has exactly one parent. Each lord $i$ has a required amount of money $m_i$. Money flows through this tree in a very specific...

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CF 1560F1 - Nearest Beautiful Number (easy version)

CF 1560F1 - Nearest Beautiful Number (easy version) Rating: 1900 Tags: binary search, bitmasks, brute force, constructive algorithms, dfs and similar, greedy Solve time: 7m 52s Verified: no Solution Problem Understanding We are given a starting number and a restriction on how many distinct digits we are allowed to use. For each query, we must find the smallest integer that is not smaller than the given number and whose decimal...

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CF 1551F - Equidistant Vertices

CF 1551F - Equidistant Vertices Rating: 2200 Tags: brute force, combinatorics, dfs and similar, dp, trees Solve time: 3m 54s Verified: yes Solution Problem Understanding The task is about selecting a subset of vertices in a tree such that every pair of chosen vertices is equally far apart. Instead of just picking arbitrary nodes, we want a very rigid geometric configuration: once you pick the subset, all pairwise distances must...

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Codeforces Round 736 (Div. 2)

Codeforces Round 736 (Div. 2) Div. 2 | 2 problems | 0/2 verified | Difficulty 800-800 | 11m 31s # Problem Rating Tags Accepted Time ✓ A Gregor and Cryptography 800 math, number-theory 35,559 3m 41s B Gregor and the Pawn Game 800 dfs-and-similar, dp, flows 26,817 7m 50s

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CF 1549B - Gregor and the Pawn Game

CF 1549B - Gregor and the Pawn Game Rating: 800 Tags: dfs and similar, dp, flows, graph matchings, graphs, greedy, implementation Solve time: 7m 50s Verified: no Solution Problem Understanding We are given a square board of size $n \times n$, but only the first and last rows matter. The bottom row contains Gregor’s pawns, and the top row contains enemy pawns. Every column is either empty or occupied independently...

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CF 1547G - How Many Paths?

CF 1547G - How Many Paths? Rating: 2100 Tags: dfs and similar, dp, graphs, trees Solve time: 8m 54s Verified: no Solution Problem Understanding We are given a directed graph where we start from node 1 and consider all possible directed walks that end at each vertex. A walk can revisit nodes and edges arbitrarily many times. For every vertex, we are not asked to compute the exact number of...

Practice › Codeforces Solutions › Codeforces Round 730 (Div. 2) ›

CF 1543C - Need for Pink Slips

CF 1543C - Need for Pink Slips Rating: 1900 Tags: bitmasks, brute force, dfs and similar, implementation, math, probabilities Solve time: 6m 31s Verified: no Solution Problem Understanding We are repeatedly running a stochastic process that evolves a small probability distribution over three outcomes. At any moment there are up to three “active” slips, one of which is a terminal success state (the pink slip) and the other two are...

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CF 1533I - Excursions

CF 1533I - Excursions Rating: - Tags: *special, constructive algorithms, dfs and similar, flows, graph matchings, graphs Solve time: 7m 26s Verified: yes Solution Problem Understanding We can view the situation as a two-layer directed routing process between two bipartite sets of nodes. One set corresponds to sights in Saratov, the other to sights in Engels. Each bus route is bidirectional in the sense that it can be used in...

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CF 1533G - Biome Map

CF 1533G - Biome Map Rating: - Tags: *special, constructive algorithms, dfs and similar, graphs Solve time: 5m 39s Verified: no Solution Problem Understanding We are given a small grid of biome “types”, where each type is identified by a pair of parameters coming from a fixed $n \times m$ table. Some of these pairs exist and are assigned a unique integer identifier, while others are unavailable. Our task is...

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CF 1499F - Diameter Cuts

CF 1499F - Diameter Cuts Rating: 2400 Tags: combinatorics, dfs and similar, dp, trees Solve time: 3m 41s Verified: yes Solution Problem Understanding We are working with a tree where every edge is initially present. We are allowed to remove any subset of edges, which splits the tree into several connected components. Each resulting component is still a tree. The condition we must enforce is local to each resulting component:...

Practice › Codeforces Solutions › Technocup 2021 - Elimination Round 3 ›

CF 1411C - Peaceful Rooks

CF 1411C - Peaceful Rooks Rating: 1700 Tags: dfs and similar, dsu, graphs Solve time: 8m 35s Verified: no Solution Problem Understanding We are given a chessboard where no two rooks initially share a row or a column, so every rook sits in a distinct row and a distinct column. A move allows us to pick one rook and slide it any distance in a straight horizontal or vertical line,...

Practice › Codeforces Solutions › Codeforces Round 668 (Div. 1) ›

CF 1404D - Game of Pairs

CF 1404D - Game of Pairs Rating: 2800 Tags: constructive algorithms, dfs and similar, interactive, math, number theory Solve time: 4m 8s Verified: no Solution Problem Understanding We are working with a two-player construction game on the numbers from 1 to 2n. One player first partitions these numbers into n disjoint pairs. After that, the second player selects exactly one number from each pair. The score is the sum of...

Practice › Codeforces Solutions › Codeforces Round 668 (Div. 1) ›

CF 1404B - Tree Tag

CF 1404B - Tree Tag Rating: 1900 Tags: dfs and similar, dp, games, trees Solve time: 3m 37s Verified: yes Solution Problem Understanding We are given a tree where two players start on different vertices. Alice moves first. On each turn, Alice can jump to any vertex within distance da , and Bob can jump to any vertex within distance db . Distance is standard shortest path length in the...

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Codeforces Round 595 (Div. 3)

Codeforces Round 595 (Div. 3) Div. 3 | 9 problems | 5/9 verified | Difficulty 800-2200 | 43m 43s # Problem Rating Tags Accepted Time ✓ A Yet Another Dividing into Teams 800 math 23,707 2m 20s ✓ B1 Books Exchange (easy version) 1000 dsu, math 22,287 5m 26s B2 Books Exchange (hard version) 1300 dfs-and-similar, dsu, math 18,391 4m 6s C1 Good Numbers (easy version) 1300 brute-force, greedy, implementation...

Practice › Codeforces Solutions › Bubble Cup 12 - Finals [Online Mirror, unrated, Div. 1] ›

CF 1218H - Function Composition

CF 1218H - Function Composition Rating: 2900 Tags: dfs and similar Solve time: 4m 2s Verified: yes Solution Problem Understanding We are given a directed functional graph defined by an array A . From every node i , there is exactly one outgoing edge to A[i] . Repeated application of this mapping defines a process where starting from a node x , we move along the graph m times. The...

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Codeforces Round 599 (Div. 1)

Codeforces Round 599 (Div. 1) Div. 1 | 5 problems | 2/5 verified | Difficulty 1500-3400 | 17m 26s # Problem Rating Tags Accepted Time ✓ A Tile Painting 1500 constructive-algorithms, math, number-theory 13,265 6m 35s ✓ B 0-1 MST 1900 dfs-and-similar, dsu, graphs 9,241 5m 48s ✓ C Sum Balance 2400 bitmasks, dfs-and-similar, dp 1,947 1m 43s D Number Discovery 3400 math 234 1m 42s E Planar Perimeter 3200...

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Codeforces Round 536 (Div. 2)

Codeforces Round 536 (Div. 2) Div. 2 | 5 problems | 5/5 verified | Difficulty 800-2400 | 16m 55s # Problem Rating Tags Accepted Time ✓ A Lunar New Year and Cross Counting 800 implementation 12,864 4m 34s ✓ C Lunar New Year and Number Division 900 greedy, implementation, math 15,906 1m 15s ✓ D Lunar New Year and a Wander 1500 data-structures, dfs-and-similar, graphs 19,644 4m 40s ✓ E...

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Codeforces Round 534 (Div. 1)

Codeforces Round 534 (Div. 1) Div. 1 | 4 problems | 3/4 verified | Difficulty 1400-3100 | 11m 18s # Problem Rating Tags Accepted Time ✓ A Grid game 1400 constructive-algorithms, implementation 10,596 3m 23s ✓ B Game with modulo 2000 binary-search, constructive-algorithms, interactive 3,528 1m 38s C Johnny Solving 2700 constructive-algorithms, dfs-and-similar, graphs 953 4m 21s ✓ D Professional layer 3100 bitmasks, dp 493 1m 56s ✓

Practice › Codeforces Solutions › Codeforces Round 578 (Div. 2) ›

CF 1200F - Graph Traveler

CF 1200F - Graph Traveler Rating: 2300 Tags: brute force, data structures, dfs and similar, dp, graphs, implementation, math, number theory Solve time: 5m 16s Verified: no Solution Problem Understanding We are given a directed graph where each vertex behaves like a deterministic machine with a twist: the outgoing edge is not fixed, but chosen based on a changing integer state $c$. Every time we arrive at a vertex, we...

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CF 1192B - Dynamic Diameter

CF 1192B - Dynamic Diameter Rating: - Tags: *special, data structures, dfs and similar, divide and conquer, trees Solve time: 3m 58s Verified: no Solution

Practice › Codeforces Solutions › Codeforces Round 572 (Div. 1) ›

CF 1188A2 - Add on a Tree: Revolution

CF 1188A2 - Add on a Tree: Revolution Rating: 2500 Tags: constructive algorithms, dfs and similar, implementation, trees Solve time: 6m 56s Verified: no Solution I cannot reliably reconstruct the exact statement of Codeforces 1188A2 (“Add on a Tree: Revolution”) from memory alone, and this problem is one of those 2500-rated constructives where small misinterpretations completely change the solution. If I invent missing constraints, the editorial would be misleading rather...

Practice › Codeforces Solutions › Educational Codeforces Round 67 (Rated for Div. 2) ›

CF 1187E - Tree Painting

CF 1187E - Tree Painting Rating: 2100 Tags: dfs and similar, dp, trees Solve time: 8m 22s Verified: no Solution Problem Understanding We are given a tree where every vertex starts unpainted, and we gradually paint vertices black. The first move can start anywhere, and after that every move must pick a white vertex that is adjacent to at least one black vertex. Each time we paint a vertex, we...

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Codeforces Round 571 (Div. 2)

Codeforces Round 571 (Div. 2) Type: Div. 2 | Problems: 5 | Verified: 2/5 | Rating range: 800-2500 | Time: 23m 39s Problem Name Rating Tags Solve Time Verified A Vus the Cossack and a Contest 800 implementation 3m 8s ✓ C Vus the Cossack and Strings 1800 implementation, math 3m 23s ✓ D Vus the Cossack and Numbers 1500 constructive-algorithms, greedy, math 4m 36s ✗ E Vus the Cossack...

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CF 1186F - Vus the Cossack and a Graph

CF 1186F - Vus the Cossack and a Graph Rating: 2400 Tags: dfs and similar, graphs, greedy, implementation Solve time: 6m 47s Verified: no Solution Problem Understanding We are given an undirected simple graph. Every vertex has some initial degree, and we are allowed to delete edges. After deletions, each vertex must still keep at least half of its original incident edges, rounded up. At the same time, the total...

Practice › Codeforces Solutions › Helvetic Coding Contest 2019 online mirror (teams allowed, unrated) ›

CF 1184E2 - Daleks' Invasion (medium)

CF 1184E2 - Daleks' Invasion (medium) Rating: 2100 Tags: dfs and similar, graphs, shortest paths, trees Solve time: 10m 39s Verified: yes Solution Problem Understanding We are given a connected undirected graph where each edge represents a corridor with a unique energy cost. The Daleks always intend to build a minimum spanning tree, so among all possible spanning trees they will pick the one with minimum total cost, which is...

Practice › Codeforces Solutions › Codeforces Round 566 (Div. 2) ›

CF 1182B - Plus from Picture

CF 1182B - Plus from Picture Rating: 1300 Tags: dfs and similar, implementation, strings Solve time: 11m 19s Verified: yes Solution Problem Understanding We are given a grid of characters representing a picture, where each cell is either empty or filled. The task is to decide whether the filled cells form exactly one plus-shaped figure. A valid plus shape has a single central filled cell. From that center, there must...

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CF 1178G - The Awesomest Vertex

CF 1178G - The Awesomest Vertex Rating: 3000 Tags: data structures, dfs and similar Solve time: 8m 35s Verified: no Solution Problem Understanding We are working with a rooted tree where every node contributes two values, a_i and b_i . For any node v , consider the path from the root down to v . Along this path we accumulate the sums of a values and b values separately. The...

Practice › Codeforces Solutions › Codeforces Round 565 (Div. 3) ›

CF 1176E - Cover it!

CF 1176E - Cover it! Rating: 1700 Tags: dfs and similar, dsu, graphs, shortest paths, trees Solve time: 10m 33s Verified: no Solution Problem Understanding We are given an undirected connected graph for each query, and we must select a subset of vertices such that every vertex we do not select has at least one selected neighbor. In other words, every unchosen vertex must be “covered” by an adjacent chosen...

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CF 1176D - Recover it!

CF 1176D - Recover it! Rating: 1800 Tags: dfs and similar, graphs, greedy, number theory, sortings Solve time: 9m 59s Verified: no Solution Problem Understanding We are given an unknown array of integers. Each original value is between 2 and 200000. From this hidden array, a second array is produced by expanding every element into two values and then shuffling everything. Our task is to reconstruct any original array that...

Practice › Codeforces Solutions › Codeforces Round 536 (Div. 2) ›

CF 1106D - Lunar New Year and a Wander

CF 1106D - Lunar New Year and a Wander Rating: 1500 Tags: data structures, dfs and similar, graphs, greedy, shortest paths Solve time: 4m 40s Verified: yes Solution Problem Understanding We are given an undirected connected graph with $n$ nodes. Bob starts at node 1 and performs a walk along edges. Every time he enters a node that has never been seen before, he writes it down. The walk continues...

Practice › Codeforces Solutions › Codeforces Round 533 (Div. 2) ›

CF 1105D - Kilani and the Game

CF 1105D - Kilani and the Game Rating: 1900 Tags: dfs and similar, graphs, implementation, shortest paths Solve time: 5m 10s Verified: yes Solution Problem Understanding We are given a rectangular grid where each cell is either blocked, empty, or already owned by one of up to nine players. Each player starts with some initial castles placed on the grid, and each player also has a fixed expansion strength that...

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Educational Codeforces Round 58 (Rated for Div. 2)

Educational Codeforces Round 58 (Rated for Div. 2) Type: Div. 2 | Problems: 7 | Verified: 5/7 | Rating range: 1000-2400 | Time: 33m 51s Problem Name Rating Tags Solve Time Verified A Minimum Integer 1000 math 5m 4s ✓ B Accordion 1300 greedy, implementation 1m 13s ✓ C Division and Union 1500 sortings 6m 57s ✗ D GCD Counting 2000 data-structures, dfs-and-similar, dp 4m 55s ✓ E Polycarp's New...

Practice › Codeforces Solutions › Educational Codeforces Round 58 (Rated for Div. 2) ›

CF 1101D - GCD Counting

CF 1101D - GCD Counting Rating: 2000 Tags: data structures, dfs and similar, dp, number theory, trees Solve time: 4m 55s Verified: yes Solution Problem Understanding We are given a tree where each node carries an integer label. For any two vertices, consider the unique simple path between them. Along that path we look at all vertex values and compute their greatest common divisor. We are interested only in pairs...

Practice › Codeforces Solutions › Educational Codeforces Round 56 (Rated for Div. 2) ›

CF 1093D - Beautiful Graph

CF 1093D - Beautiful Graph Rating: 1700 Tags: dfs and similar, graphs Solve time: 3m 33s Verified: yes Solution Problem Understanding We are given an undirected graph and asked to assign each vertex one value from the set {1, 2, 3}. The assignment is valid only if every edge connects two vertices whose values sum to an odd number. The task is to count how many such assignments exist, taken...

Practice › Codeforces Solutions › Codeforces Round 527 (Div. 3) ›

CF 1092F - Tree with Maximum Cost

CF 1092F - Tree with Maximum Cost Rating: 1900 Tags: dfs and similar, dp, trees Solve time: 7m 47s Verified: no Solution Problem Understanding We are given a weighted tree, where each node carries a positive value. We are allowed to choose any node as a reference point, and for that choice we compute a score defined as the sum over all nodes of their value multiplied by their distance...

Practice › Codeforces Solutions › Codeforces Round 527 (Div. 3) ›

CF 1092E - Minimal Diameter Forest

CF 1092E - Minimal Diameter Forest Rating: 2000 Tags: constructive algorithms, dfs and similar, greedy, trees Solve time: 5m 14s Verified: no Solution Problem Understanding We are given a graph that is already a forest, meaning it consists of several disconnected trees. The task is to add exactly enough edges to connect all these trees into a single tree. Since a tree on n vertices has exactly n - 1...

Practice › Codeforces Solutions › 2018-2019 ICPC, NEERC, Northern Eurasia Finals (Unrated, Online Mirror, ICPC Rules, Teams Preferred) ›

CF 1089H - Harder Satisfiability

CF 1089H - Harder Satisfiability Rating: 3400 Tags: 2-sat, dfs and similar, graphs Solve time: 2m 35s Verified: yes Solution Problem Understanding We are given a logical system built from boolean variables, where constraints are expressed as implications between literals. Each variable can be either true or false, and every constraint restricts how assignments interact, typically in a way that can be interpreted as implications like “if this literal is...

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Codeforces Round 465 (Div. 2)

Codeforces Round 465 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 4/6 | Rating range: 800-2600 | Time: 33m 56s Problem Name Rating Tags Solve Time Verified A Fafa and his Company 800 brute-force, implementation 9m 9s ✓ B Fafa and the Gates 900 implementation 2m 57s ✓ C Fifa and Fafa 1600 geometry 4m ✗ D Fafa and Ancient Alphabet 1900 math, probabilities 4m 24s ✓ E...

Practice › Codeforces Solutions › Codeforces Round 465 (Div. 2) ›

CF 935E - Fafa and Ancient Mathematics

CF 935E - Fafa and Ancient Mathematics Rating: 2300 Tags: dfs and similar, dp, trees Solve time: 4m 3s Verified: yes Solution Problem Understanding We are given a fully parenthesized arithmetic expression shaped like a binary tree. Every internal node is an operator, and every leaf is a single digit. However, all operators have been erased and replaced by placeholders. We also know exactly how many plus and minus signs...

Practice › Codeforces Solutions › Educational Codeforces Round 37 (Rated for Div. 2) ›

CF 920E - Connected Components?

CF 920E - Connected Components? Rating: 2100 Tags: data structures, dfs and similar, dsu, graphs Solve time: 2m 56s Verified: yes Solution Problem Understanding The graph in this problem is not given in the usual way. Instead of listing edges that exist, the input lists pairs of vertices that are explicitly disconnected. Every pair of vertices that does not appear in this list should be treated as having an edge...

Practice › Codeforces Solutions › Educational Codeforces Round 37 (Rated for Div. 2) ›

CF 920C - Swap Adjacent Elements

CF 920C - Swap Adjacent Elements Rating: 1400 Tags: dfs and similar, greedy, math, sortings, two pointers Solve time: 2m 30s Verified: yes Solution Problem Understanding We are given a permutation of size n, meaning every integer from 1 to n appears exactly once. Alongside this array is a string that describes which adjacent positions are “connected” by an allowed swap. If the i-th character is 1, we are allowed...

Practice › Codeforces Solutions › Codeforces Round 460 (Div. 2) ›

CF 919D - Substring

CF 919D - Substring Rating: 1700 Tags: dfs and similar, dp, graphs Solve time: 12m 47s Verified: yes Solution Problem Understanding We are given a directed graph where each vertex carries a lowercase letter. A valid walk follows directed edges from node to node, and we are allowed to revisit nodes and edges as long as we respect direction. For any such walk, we look at the sequence of letters...

Practice › Codeforces Solutions › Codeforces Round 459 (Div. 1) ›

CF 917B - MADMAX

CF 917B - MADMAX Rating: 1700 Tags: dfs and similar, dp, games, graphs Solve time: 4m 34s Verified: no Solution Problem Understanding We are given a directed acyclic graph where each edge carries a lowercase letter. Two tokens start on possibly different vertices: one belongs to Max and one to Lucas. They take turns moving their own token along outgoing edges, and the twist is that the letters along the...

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Educational Codeforces Round 36 (Rated for Div. 2)

Educational Codeforces Round 36 (Rated for Div. 2) Type: Div. 2 | Problems: 7 | Verified: 4/7 | Rating range: 900-2400 | Time: 57m 49s Problem Name Rating Tags Solve Time Verified A Garden 900 implementation 11m 44s ✓ B Browser 1300 implementation 5m 31s ✓ C Permute Digits 1700 dp, greedy 3m 31s ✓ D Almost Acyclic Graph 2200 dfs-and-similar, graphs 3m 24s ✓ E Physical Education Lessons 2300...

Practice › Codeforces Solutions › Educational Codeforces Round 36 (Rated for Div. 2) ›

CF 915D - Almost Acyclic Graph

CF 915D - Almost Acyclic Graph Rating: 2200 Tags: dfs and similar, graphs Solve time: 3m 24s Verified: yes Solution Problem Understanding We are given a directed graph with n vertices and m edges. Each edge has a direction from some vertex u to another vertex v . The task is to determine whether we can remove at most one edge to make the graph acyclic. A directed graph is...

Practice › Codeforces Solutions › Educational Codeforces Round 35 (Rated for Div. 2) ›

CF 911F - Tree Destruction

CF 911F - Tree Destruction Rating: 2400 Tags: constructive algorithms, dfs and similar, graphs, greedy, trees Solve time: 14m 49s Verified: no Solution Problem Understanding We are asked to process a tree with n vertices by performing n - 1 operations that each choose two leaves, add the distance between them to a running total, and remove one of the leaves. The goal is to maximize the total sum of...

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CF 910A - The Way to Home

CF 910A - The Way to Home Rating: 800 Tags: dfs and similar, dp, greedy, implementation Solve time: 12m 30s Verified: yes Solution Problem Understanding We are given a one-dimensional line of positions from 1 to n. Some positions contain a lily, represented by a 1 , while others are empty, represented by a 0 . A frog starts at position 1 and wants to reach position n. From any...

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Testing Round 14 (Unrated)

Testing Round 14 (Unrated) Type: Special | Problems: 3 | Verified: 1/3 | Rating range: 800-1700 | Time: 26m 11s Problem Name Rating Tags Solve Time Verified A The Way to Home 800 dfs-and-similar, dp, greedy 12m 30s ✓ B Door Frames 1600 greedy, implementation 9m 58s ✗ C Minimum Sum 1700 constructive-algorithms, greedy, math 3m 43s ✗

Practice › Codeforces Solutions › Codeforces Round 453 (Div. 2) ›

CF 902B - Coloring a Tree

CF 902B - Coloring a Tree Rating: 1200 Tags: dfs and similar, dsu, greedy Solve time: 4m 37s Verified: yes Solution Problem Understanding We are given a rooted tree with n vertices, where vertex 1 is the root. Each vertex must be colored with a target color specified in the input. Initially, all vertices are color 0. A coloring operation consists of picking any vertex v and a color x...

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CEOI 2019 day 1 online mirror (unrated, IOI format)

CEOI 2019 day 1 online mirror (unrated, IOI format) Type: ICPC/IOI | Problems: 3 | Verified: 2/3 | Rating range: - | Time: 12m 44s Problem Name Rating Tags Solve Time Verified A Building Skyscrapers - *special 1m 29s ✓ B Dynamic Diameter - *special, data-structures, dfs-and-similar 3m 58s ✗ C Cubeword - *special, brute-force, dp 7m 17s ✓

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Codeforces Round 572 (Div. 1)

Codeforces Round 572 (Div. 1) Type: Div. 1 | Problems: 6 | Verified: 4/6 | Rating range: 1600-3300 | Time: 24m 42s Problem Name Rating Tags Solve Time Verified A1 Add on a Tree 1600 trees 1m 48s ✓ A2 Add on a Tree: Revolution 2500 constructive-algorithms, dfs-and-similar, implementation 6m 56s ✗ B Count Pairs 2300 math, matrices, number-theory 3m 35s ✓ C Array Beauty 2500 dp 4m 40s ✗...

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Educational Codeforces Round 37 (Rated for Div. 2)

Educational Codeforces Round 37 (Rated for Div. 2) Div. 2 | 7 problems | 6/7 verified | Difficulty 1000-2400 | 30m 58s # Problem Rating Tags Accepted Time ✓ A Water The Garden 1000 implementation 8,195 2m 8s ✓ B Tea Queue 1200 implementation 8,101 5m 21s C Swap Adjacent Elements 1400 dfs-and-similar, greedy, math 9,970 2m 30s ✓ D Tanks 2400 dp, greedy, implementation 809 10m 3s ✓ E...

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Codeforces Round 566 (Div. 2)

Codeforces Round 566 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 3/6 | Rating range: 1000-2700 | Time: 28m 58s Problem Name Rating Tags Solve Time Verified A Filling Shapes 1000 dp, math 1m 23s ✓ B Plus from Picture 1300 dfs-and-similar, implementation, strings 11m 19s ✓ C Beautiful Lyrics 1700 data-structures, greedy, strings 3m 38s ✗ D Complete Mirror 2400 constructive-algorithms, dfs-and-similar, dp 1m 17s ✓ E...

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Codeforces Round 565 (Div. 3)

Codeforces Round 565 (Div. 3) Type: Div. 3 | Problems: 6 | Verified: 4/6 | Rating range: 800-2100 | Time: 31m 28s Problem Name Rating Tags Solve Time Verified A Divide it! 800 brute-force, greedy, implementation 1m 23s ✓ B Merge it! 1100 math 4m ✓ C Lose it! 1300 dp, greedy, implementation 4m 7s ✓ D Recover it! 1800 dfs-and-similar, graphs, greedy 9m 59s ✗ E Cover it! 1700...

Practice › Codeforces Solutions › CodeCraft-19 and Codeforces Round 537 (Div. 2) ›

CF 1111E - Tree

CF 1111E - Tree Rating: 2500 Tags: data structures, dfs and similar, dp, graphs, trees Solve time: 1m 26s Verified: no Solution Problem Understanding We are given a tree with n nodes and multiple queries. Each query provides a subset of k nodes, a maximum number of groups m , and a root r . The task is to partition the given nodes into at most m groups with the...

Practice › Codeforces Solutions › Codeforces Round 540 (Div. 3) ›

CF 1118F2 - Tree Cutting (Hard Version)

CF 1118F2 - Tree Cutting (Hard Version) Rating: 2700 Tags: combinatorics, dfs and similar, dp, trees Solve time: 1m 22s Verified: no Solution Problem Understanding We are given a tree with $n$ vertices. Each vertex is either colored with one of $k$ colors or left uncolored. The tree is connected, so there are $n-1$ edges. We are asked to select exactly $k-1$ edges and remove them, splitting the tree into...

Practice › Codeforces Solutions › Codeforces Round 540 (Div. 3) ›

CF 1118F1 - Tree Cutting (Easy Version)

CF 1118F1 - Tree Cutting (Easy Version) Rating: 1800 Tags: dfs and similar, trees Solve time: 1m 4s Verified: yes Solution Problem Understanding We are given a tree with n vertices, where each vertex may be colored red, blue, or left uncolored. The task is to count edges that, when removed, separate the tree into two components such that neither component contains both red and blue vertices. In other words,...

Practice › Codeforces Solutions › Codeforces Round 543 (Div. 1, based on Technocup 2019 Final Round) ›

CF 1120D - Power Tree

CF 1120D - Power Tree Rating: 2500 Tags: dfs and similar, dp, dsu, graphs, greedy, trees Solve time: 1m 33s Verified: no Solution Problem Understanding We are given a rooted tree with n vertices, where each vertex has a non-negative price. The root is vertex 1. Leaves are non-root vertices with degree one. Arkady wants to buy a subset of vertices and then, regardless of what numbers Vasily assigns to...

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Codeforces Round 542 [Alex Lopashev Thanks-Round] (Div. 2)

Codeforces Round 542 [Alex Lopashev Thanks-Round] (Div. 2) Type: Div. 2 | Problems: 3 | Verified: 2/3 | Rating range: 800-1400 | Time: 4m 41s Problem Name Rating Tags Solve Time Verified A Be Positive 800 implementation 1m 52s ✗ B Two Cakes 1200 greedy 1m 35s ✓ C Connect 1400 brute-force, dfs-and-similar, dsu 1m 14s ✓

Practice › Codeforces Solutions › Codeforces Round 542 [Alex Lopashev Thanks-Round] (Div. 2) ›

CF 1130C - Connect

CF 1130C - Connect Rating: 1400 Tags: brute force, dfs and similar, dsu Solve time: 1m 14s Verified: yes Solution Problem Understanding We are given a square grid representing a planet with land and water. Alice starts at one land cell and wants to reach another land cell. She can only walk on land, moving orthogonally between adjacent cells. If a path exists naturally, she can reach her destination at...

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Codeforces Round 541 (Div. 2)

Codeforces Round 541 (Div. 2) Type: Div. 2 | Problems: 7 | Verified: 4/7 | Rating range: 800-2700 | Time: 10m 40s Problem Name Rating Tags Solve Time Verified A Sea Battle 800 math 2m 2s ✓ B Draw! 1400 greedy, implementation 1m 16s ✓ C Birthday 1200 binary-search, greedy, sortings 1m 28s ✓ D Gourmet choice 2000 dfs-and-similar, dp, dsu 1m 28s ✗ E String Multiplication 2300 dp, greedy,...

Practice › Codeforces Solutions › Codeforces Round 541 (Div. 2) ›

CF 1131D - Gourmet choice

CF 1131D - Gourmet choice Rating: 2000 Tags: dfs and similar, dp, dsu, graphs, greedy Solve time: 1m 28s Verified: no Solution Problem Understanding The problem asks us to assign positive integer scores to two sets of dishes tasted by Mr. Apple on two separate days. Each dish on the first day can be compared to every dish on the second day, and the comparison is either better, worse, or...

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Educational Codeforces Round 61 (Rated for Div. 2)

Educational Codeforces Round 61 (Rated for Div. 2) Type: Div. 2 | Problems: 7 | Verified: 6/7 | Rating range: 900-2400 | Time: 10m 4s Problem Name Rating Tags Solve Time Verified A Regular Bracket Sequence 1100 greedy, implementation 1m 10s ✓ B Discounts 900 greedy, sortings 1m 13s ✓ C Painting the Fence 1700 brute-force 2m 2s ✓ D Stressful Training 2300 binary-search, greedy 1m 23s ✗ E Knapsack...

Practice › Codeforces Solutions › Educational Codeforces Round 61 (Rated for Div. 2) ›

CF 1132E - Knapsack

CF 1132E - Knapsack Rating: 2300 Tags: dfs and similar, dp, greedy Solve time: 1m 11s Verified: yes Solution Problem Understanding We are given a multiset of items where every item has a weight between 1 and 8 inclusive. The number of items of each weight is extremely large, but only their counts matter, not their identities. From this multiset we want to choose some subset of items such that...

Practice › Codeforces Solutions › Codeforces Round 544 (Div. 3) ›

CF 1133F2 - Spanning Tree with One Fixed Degree

CF 1133F2 - Spanning Tree with One Fixed Degree Rating: 1900 Tags: constructive algorithms, dfs and similar, dsu, graphs, greedy Solve time: 1m 31s Verified: no Solution Problem Understanding We are given a connected undirected simple graph and asked to construct a spanning tree using only existing edges. The additional constraint is that vertex 1 must have degree exactly D in the chosen tree. A spanning tree is a subset...

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Codeforces Round 548 (Div. 2)

Codeforces Round 548 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 6/6 | Rating range: 800-2500 | Time: 8m 42s Problem Name Rating Tags Solve Time Verified A Even Substrings 800 implementation, strings 1m 8s ✓ B Chocolates 1000 greedy, implementation 1m 27s ✓ C Edgy Trees 1500 dfs-and-similar, dsu, graphs 1m 26s ✓ D Steps to One 2300 dp, math, number-theory 1m 39s ✓ E Maximize Mex...

Practice › Codeforces Solutions › Codeforces Round 548 (Div. 2) ›

CF 1139C - Edgy Trees

CF 1139C - Edgy Trees Rating: 1500 Tags: dfs and similar, dsu, graphs, math, trees Solve time: 1m 26s Verified: yes Solution Problem Understanding We have a tree whose edges are colored either red ( 0 ) or black ( 1 ). We must count how many sequences of length k consisting of tree vertices are "good". For a sequence [a₁, a₂, ..., aₖ] , we repeatedly travel along the...

Practice › Codeforces Solutions › Codeforces Round 547 (Div. 3) ›

CF 1141G - Privatization of Roads in Treeland

CF 1141G - Privatization of Roads in Treeland Rating: 1900 Tags: binary search, constructive algorithms, dfs and similar, graphs, greedy, trees Solve time: 1m 32s Verified: yes Solution Problem Understanding We are given a tree with $n$ vertices and $n-1$ edges. Every edge must be assigned a company number. A city is considered good if all roads incident to it belong to different companies. A city becomes bad if at...

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Codeforces Round 549 (Div. 1)

Codeforces Round 549 (Div. 1) Type: Div. 1 | Problems: 5 | Verified: 1/5 | Rating range: 1700-3200 | Time: 8m 46s Problem Name Rating Tags Solve Time Verified A The Beatles 1700 brute-force, math 1m 35s ✓ B Lynyrd Skynyrd 2000 data-structures, dfs-and-similar, dp 2m 7s ✗ C U2 2400 geometry 1m 48s ✗ D Foreigner 2800 dp 1m 44s ✗ E Pink Floyd 3200 graphs, interactive 1m 32s...

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CF 1142B - Lynyrd Skynyrd

CF 1142B - Lynyrd Skynyrd Rating: 2000 Tags: data structures, dfs and similar, dp, math, trees Solve time: 2m 7s Verified: no Solution Problem Understanding We are given a fixed permutation of numbers from 1 to n. Separately, we have a longer array whose elements also lie in the range 1 to n, but may repeat. The task is to answer many queries on subsegments of this array. For each...

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Codeforces Round 549 (Div. 2)

Codeforces Round 549 (Div. 2) Type: Div. 2 | Problems: 3 | Verified: 3/3 | Rating range: 800-1400 | Time: 4m 13s Problem Name Rating Tags Solve Time Verified A The Doors 800 implementation 1m 11s ✓ B Nirvana 1200 brute-force, math, number-theory 1m 36s ✓ C Queen 1400 dfs-and-similar, trees 1m 26s ✓

Practice › Codeforces Solutions › Codeforces Round 549 (Div. 2) ›

CF 1143C - Queen

CF 1143C - Queen Rating: 1400 Tags: dfs and similar, trees Solve time: 1m 26s Verified: yes Solution Problem Understanding We are given a rooted tree with n vertices. Each vertex has a parent p_i and a respect indicator c_i . The root is special: it has p_i = -1 and c_i = 0 . The meaning of c_i is simple: c_i = 0 means the vertex respects its ancestors,...

Practice › Codeforces Solutions › Codeforces Round 550 (Div. 3) ›

CF 1144F - Graph Without Long Directed Paths

CF 1144F - Graph Without Long Directed Paths Rating: 1700 Tags: dfs and similar, graphs Solve time: 1m 35s Verified: no Solution Problem Understanding We are given a connected undirected graph with n vertices and m edges. Our task is to assign a direction to every edge so that the resulting directed graph does not contain any path of length two or more. A path of length two is simply...

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Forethought Future Cup - Elimination Round

Forethought Future Cup - Elimination Round Type: Special | Problems: 8 | Verified: 3/8 | Rating range: 800-2900 | Time: 15m 34s Problem Name Rating Tags Solve Time Verified A [Love ](https://codeforces.com/problemset/problem/1146/A) 800 implementation, strings 1m 27s ✓ B [Hate ](https://codeforces.com/problemset/problem/1146/B) 1100 implementation, strings 1m 23s ✓ C Tree Diameter 1700 bitmasks, graphs, interactive 2m 14s ✗ D Frog Jumping 2100 dfs-and-similar, math, number-theory 3m 25s ✗ E Hot is...

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CF 1146D - Frog Jumping

CF 1146D - Frog Jumping Rating: 2100 Tags: dfs and similar, math, number theory Solve time: 3m 25s Verified: no Solution Problem Understanding A frog starts at position 0 on a number line. From any position, it can move forward by adding a or move backward by subtracting b . However, during the process of exploring what is reachable, we only allow it to stay within the segment [0, x]...

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Forethought Future Cup - Final Round (Onsite Finalists Only)

Forethought Future Cup - Final Round (Onsite Finalists Only) Type: Special | Problems: 6 | Verified: 2/6 | Rating range: 1500-3500 | Time: 9m 37s Problem Name Rating Tags Solve Time Verified A Hide and Seek 1500 graphs 1m 51s ✗ B Chladni Figure 1900 brute-force, strings 1m 2s ✓ C Thanos Nim 2000 games 1m 22s ✓ D Palindrome XOR 2400 dfs-and-similar, graphs 1m 45s ✗ E Rainbow Coins...

Practice › Codeforces Solutions › Forethought Future Cup - Final Round (Onsite Finalists Only) ›

CF 1147D - Palindrome XOR

CF 1147D - Palindrome XOR Rating: 2400 Tags: dfs and similar, graphs Solve time: 1m 45s Verified: no Solution Problem Understanding We are given a binary string pattern s consisting of '1', '0', and '?', with the guarantee that the first character is '1'. The task is to count the number of pairs of positive integers (a, b) such that both a and b are binary palindromes when written without...

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Codeforces Round 554 (Div. 2)

Codeforces Round 554 (Div. 2) Type: Div. 2 | Problems: 7 | Verified: 4/7 | Rating range: 800-3000 | Time: 12m 11s Problem Name Rating Tags Solve Time Verified A Neko Finds Grapes 800 greedy, implementation, math 1m 24s ✓ B Neko Performs Cat Furrier Transform 1300 bitmasks, constructive-algorithms, dfs-and-similar 1m 43s ✗ C Neko does Maths 1800 brute-force, math, number-theory 3m 35s ✓ D Neko and Aki's Prank 2100...

Practice › Codeforces Solutions › Codeforces Round 554 (Div. 2) ›

CF 1152E - Neko and Flashback

CF 1152E - Neko and Flashback Rating: 2400 Tags: constructive algorithms, dfs and similar, graphs Solve time: 53s Verified: no Solution Problem Understanding The task is to reconstruct an array of positive integers, a , given two arrays b' and c' . These arrays were generated from a through two stages: first, by taking all consecutive pairs in a to form b and c , where each b_i is the...

Practice › Codeforces Solutions › Codeforces Round 554 (Div. 2) ›

CF 1152B - Neko Performs Cat Furrier Transform

CF 1152B - Neko Performs Cat Furrier Transform Rating: 1300 Tags: bitmasks, constructive algorithms, dfs and similar, math Solve time: 1m 43s Verified: no Solution Problem Understanding We are given a positive integer x representing the "number" of a cat. Our goal is to transform x into a number of the form 2^m - 1 for some non-negative integer m . These numbers in binary consist entirely of 1s, such...

Practice › Codeforces Solutions › Codeforces Round 551 (Div. 2) ›

CF 1153D - Serval and Rooted Tree

CF 1153D - Serval and Rooted Tree Rating: 1900 Tags: binary search, dfs and similar, dp, greedy, trees Solve time: 1m 23s Verified: yes Solution Problem Understanding We are given a rooted tree where every node either behaves like a minimum aggregator or a maximum aggregator. The leaves do not compute anything; they simply hold values. The internal nodes compute their value from their children, either taking the minimum or...

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Educational Codeforces Round 64 (Rated for Div. 2)

Educational Codeforces Round 64 (Rated for Div. 2) Type: Div. 2 | Problems: 7 | Verified: 4/7 | Rating range: 1400-2700 | Time: 10m 55s Problem Name Rating Tags Solve Time Verified A Inscribed Figures 1400 geometry 1m 31s ✓ B Ugly Pairs 1800 dfs-and-similar, greedy, implementation 1m 46s ✗ C Match Points 2000 binary-search, greedy, sortings 1m 18s ✓ D 0-1-Tree 2200 dfs-and-similar, divide-and-conquer, dp 1m 42s ✗ E...

Practice › Codeforces Solutions › Educational Codeforces Round 64 (Rated for Div. 2) ›

CF 1156D - 0-1-Tree

CF 1156D - 0-1-Tree Rating: 2200 Tags: dfs and similar, divide and conquer, dp, dsu, trees Solve time: 1m 42s Verified: no Solution Problem Understanding We are given a tree with n vertices, where each edge is labeled either 0 or 1. We need to count all ordered pairs of distinct vertices (x, y) such that, when walking along the unique path from x to y , we never traverse...

Practice › Codeforces Solutions › Educational Codeforces Round 64 (Rated for Div. 2) ›

CF 1156B - Ugly Pairs

CF 1156B - Ugly Pairs Rating: 1800 Tags: dfs and similar, greedy, implementation, sortings, strings Solve time: 1m 46s Verified: no Solution Problem Understanding We are given a short string of lowercase letters and we are allowed to reorder its characters arbitrarily. The goal is to produce an arrangement where no two adjacent characters differ by exactly one position in the alphabet. For example, placing ‘c’ next to ‘d’ or...

Practice › Codeforces Solutions › Codeforces Round 559 (Div. 1) ›

CF 1158C - Permutation recovery

CF 1158C - Permutation recovery Rating: 2100 Tags: constructive algorithms, data structures, dfs and similar, graphs, greedy, math, sortings Solve time: 1m 37s Verified: no Solution Problem Understanding We are asked to reconstruct a permutation of numbers from 1 to n given a partially known array called next . Each element next[i] represents the smallest index j greater than i such that p[j] > p[i] . If no such j...

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Codeforces Round 459 (Div. 1)

Codeforces Round 459 (Div. 1) Type: Div. 1 | Problems: 5 | Verified: 2/5 | Rating range: 1700-3400 | Time: 25m 47s Problem Name Rating Tags Solve Time Verified A The Monster 1800 dp, greedy, implementation 2m 41s ✓ B MADMAX 1700 dfs-and-similar, dp, games 4m 34s ✗ C Pollywog 2900 combinatorics, dp, matrices 6m 26s ✗ D Stranger Trees 2600 dp, math, matrices 9m 19s ✗ E Upside Down...

Practice › Codeforces Solutions › Educational Codeforces Round 65 (Rated for Div. 2) ›

CF 1167C - News Distribution

CF 1167C - News Distribution Rating: 1400 Tags: dfs and similar, dsu, graphs Solve time: 3m 18s Verified: yes Solution Problem Understanding We are given a social network with n users and m groups of friends. Each group contains a list of users who are mutually friends with each other. Friendship is transitive through these groups: if two users are in the same group, they are friends, and the news...

Practice › Codeforces Solutions › Codeforces Round 564 (Div. 1) ›

CF 1172B - Nauuo and Circle

CF 1172B - Nauuo and Circle Rating: 1900 Tags: combinatorics, dfs and similar, dp, trees Solve time: 1m 31s Verified: yes Solution Problem Understanding We are asked to count how many ways we can place the nodes of a given tree around a circle such that the edges, drawn as straight lines between nodes, do not cross. The tree has n nodes labeled from 1 to n , and n-1...

Practice › Codeforces Solutions › Educational Codeforces Round 66 (Rated for Div. 2) ›

CF 1175E - Minimal Segment Cover

CF 1175E - Minimal Segment Cover Rating: 2200 Tags: data structures, dfs and similar, divide and conquer, dp, greedy, implementation, trees Solve time: 1m 38s Verified: yes Solution Problem Understanding We are given a collection of line segments on a number line and multiple queries asking about subranges. For each query segment $[x, y]$, we want to know the smallest number of given segments whose union fully covers every real...

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CF 1178F1 - Short Colorful Strip

CF 1178F1 - Short Colorful Strip Rating: 2200 Tags: combinatorics, dfs and similar, dp Solve time: 3m 59s Verified: yes Solution Problem Understanding The final strip consists of n unit segments, and because n = m in this subtask, every colour from 1 to n appears exactly once. The input array is simply a permutation describing the visible colour on each unit segment after all repainting operations have finished. Initially...

Practice › Codeforces Solutions › Codeforces Round 566 (Div. 2) ›

CF 1182D - Complete Mirror

CF 1182D - Complete Mirror Rating: 2400 Tags: constructive algorithms, dfs and similar, dp, hashing, implementation, trees Solve time: 1m 17s Verified: yes Solution Problem Understanding We are given a tree with $n$ vertices, described by $n-1$ edges. A tree is a connected graph without cycles. The task is to choose a vertex as a root such that all vertices at the same distance from the root have the same...

Practice › Codeforces Solutions › Educational Codeforces Round 74 (Rated for Div. 2) ›

CF 1238F - The Maximum Subtree

CF 1238F - The Maximum Subtree Rating: 2200 Tags: dfs and similar, dp, graphs, trees Solve time: 1m 56s Verified: yes Solution Problem Understanding We are given a tree and need to find the largest connected subgraph that can be represented as an intersection graph of line segments on a line. A graph is built from segments by creating one vertex per segment and connecting two vertices whenever the corresponding...

Practice › Codeforces Solutions › Codeforces Round 603 (Div. 2) ›

CF 1263F - Economic Difficulties

CF 1263F - Economic Difficulties Rating: 2400 Tags: data structures, dfs and similar, dp, flows, graphs, trees Solve time: 1m 44s Verified: yes Solution Problem Understanding We have two independent electrical grids in a palace, each forming a rooted tree with node 1 as the head. The trees supply electricity to devices through their leaves. Every leaf of each tree is connected to exactly one device, and each device has...

Practice › Codeforces Solutions › Codeforces Round 606 (Div. 1, based on Technocup 2020 Elimination Round 4) ›

CF 1276B - Two Fairs

CF 1276B - Two Fairs Rating: 1900 Tags: combinatorics, dfs and similar, dsu, graphs Solve time: 1m 34s Verified: yes Solution Problem Understanding We are given a connected undirected graph of cities. Among all cities, two special nodes are distinguished, call them a and b , representing two fairs. We are asked to count unordered pairs of other cities x and y such that every possible route from x to...

Practice › Codeforces Solutions › Codeforces Round 616 (Div. 1) ›

CF 1290C - Prefix Enlightenment

CF 1290C - Prefix Enlightenment Rating: 2400 Tags: dfs and similar, dsu, graphs Solve time: 1m 56s Verified: yes Solution Problem Understanding We have a line of n lamps, each either on or off. The goal is to compute, for every prefix of the lamps, the minimum number of subset toggle operations required to turn all lamps in that prefix on. The subsets are given in a way that no...

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Codeforces Round 583 (Div. 1 + Div. 2, based on Olympiad of Metropolises)

Codeforces Round 583 (Div. 1 + Div. 2, based on Olympiad of Metropolises) Div. 1+2 | 8 problems | 6/8 verified | Difficulty 1100-3200 | 25m 6s # Problem Rating Tags Accepted Time ✓ A Optimal Currency Exchange 1400 brute-force, math 9,492 2m 2s ✓ B Badges 1100 brute-force, math 11,475 5m 4s ✓ C Bad Sequence 1200 data-structures, greedy 14,197 1m 43s ✓ D Treasure Island 1900 dfs-and-similar, dp,...

Practice › Codeforces Solutions › Codeforces Round 619 (Div. 2) ›

CF 1301F - Super Jaber

CF 1301F - Super Jaber Rating: 2600 Tags: dfs and similar, graphs, implementation, shortest paths Solve time: 1m 37s Verified: yes Solution Problem Understanding We are given a rectangular grid where every cell represents a city, and each city has one of a small number of colors. From any city, Jaber can move in one second either to one of the four adjacent cells or to any other cell anywhere...

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Codeforces Round 584 - Dasha Code Championship - Elimination Round (rated, open for everyone, Div. 1 + Div. 2)

Codeforces Round 584 - Dasha Code Championship - Elimination Round (rated, open for everyone, Div. 1 + Div. 2) Div. 1+2 | 10 problems | 6/10 verified | Difficulty 800-3300 | 35m 55s # Problem Rating Tags Accepted Time ✓ A Paint the Numbers 800 greedy, implementation, math 12,841 1m 41s ✓ B Koala and Lights 1300 implementation, math, number-theory 8,515 11m 21s ✓ C Paint the Digits 1500 constructive-algorithms,...

Practice › Codeforces Solutions › Codeforces Round 620 (Div. 2) ›

CF 1304E - 1-Trees and Queries

CF 1304E - 1-Trees and Queries Rating: 2000 Tags: data structures, dfs and similar, shortest paths, trees Solve time: 1m 14s Verified: yes Solution Problem Understanding We are given a tree with $n$ vertices, where each vertex is connected such that there is exactly one path between any two vertices. Then we are asked multiple queries. Each query specifies two vertices $x$ and $y$ where we imagine adding a new...

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Technocup 2021 - Elimination Round 3

Technocup 2021 - Elimination Round 3 Special | 7 problems | 5/7 verified | Difficulty 800-3000 | 25m 35s # Problem Rating Tags Accepted Time ✓ A In-game Chat 800 implementation 21,749 1m 23s ✓ B Fair Numbers 1000 brute-force, number-theory 30,309 1m 26s ✓ C Peaceful Rooks 1700 dfs-and-similar, dsu, graphs 8,576 8m 35s D Grime Zoo 2100 brute-force, greedy, implementation 2,716 9m 23s E Poman Numbers 2300 bitmasks,...

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Codeforces Round 668 (Div. 1)

Codeforces Round 668 (Div. 1) Div. 1 | 5 problems | 2/5 verified | Difficulty 1500-2800 | 20m 9s # Problem Rating Tags Accepted Time ✓ A Balanced Bitstring 1500 implementation, strings 19,385 1m 29s ✓ B Tree Tag 1900 dfs-and-similar, dp, games 8,180 3m 37s ✓ C Fixed Point Removal 2300 binary-search, constructive-algorithms, data-structures 3,048 4m 12s D Game of Pairs 2800 constructive-algorithms, dfs-and-similar, interactive 1,270 4m 8s E...

Practice › Codeforces Solutions › Educational Codeforces Round 83 (Rated for Div. 2) ›

CF 1312G - Autocompletion

CF 1312G - Autocompletion Rating: 2600 Tags: data structures, dfs and similar, dp Solve time: 51s Verified: no Solution Problem Understanding We are given a rooted construction of many strings where every node represents a string and every edge corresponds to appending one character. The root is the empty string, and each node i is created by taking its parent string p_i and appending a lowercase letter c_i. This defines...

Practice › Codeforces Solutions › Codeforces Round 628 (Div. 2) ›

CF 1325C - Ehab and Path-etic MEXs

CF 1325C - Ehab and Path-etic MEXs Rating: 1500 Tags: constructive algorithms, dfs and similar, greedy, trees Solve time: 1m 7s Verified: no Solution Problem Understanding We are given a tree with $n$ nodes, represented by $n-1$ edges connecting pairs of nodes. Each edge must be assigned a distinct integer label between $0$ and $n-2$. For any two nodes $u$ and $v$, the MEX of the path between them is...

Practice › Codeforces Solutions › Codeforces Round 629 (Div. 3) ›

CF 1328E - Tree Queries

CF 1328E - Tree Queries Rating: 1900 Tags: dfs and similar, graphs, trees Solve time: 1m 27s Verified: no Solution Correctness The solution does not successfully establish what Exercise 4.6.3.13 asks. The positive part is that the displayed constructions are now genuine star chains. In each case the chain first builds $$1,2,4,\ldots,2^m,$$ and then appends terms by adding previously occurring powers of two. Every displayed step is indeed of the...

Practice › Codeforces Solutions › Codeforces Round 630 (Div. 2) ›

CF 1332F - Independent Set

CF 1332F - Independent Set Rating: 2500 Tags: dfs and similar, dp, trees Solve time: 1m 58s Verified: yes Solution Problem Understanding We are given a tree with $n$ vertices. For every nonempty subset of edges $E'$, we build the edge-induced subgraph consisting of those edges and every endpoint that appears in at least one selected edge. For that subgraph we count its independent sets. The task is to sum...

Practice › Codeforces Solutions › Codeforces Round 630 (Div. 2) ›

CF 1332C - K-Complete Word

CF 1332C - K-Complete Word Rating: 1500 Tags: dfs and similar, dsu, greedy, implementation, strings Solve time: 2m 56s Verified: yes Solution Problem Understanding We are given a string s of length n and an integer k such that n is divisible by k . A string is considered k -complete if it is both a palindrome and periodic with period k . Being a palindrome means the string reads...

Practice › Codeforces Solutions › Codeforces Round 639 (Div. 1) ›

CF 1344B - Monopole Magnets

CF 1344B - Monopole Magnets Rating: 2000 Tags: constructive algorithms, dfs and similar, dsu, graphs Solve time: 2m 16s Verified: yes Solution Problem Understanding We are asked to place north and south monopole magnets on an $n \times m$ grid in a way that respects three rules. Each cell is either black or white. A north magnet can move towards a south magnet in the same row or column, but...

Practice › Codeforces Solutions › Codeforces Round 641 (Div. 1) ›

CF 1349C - Orac and Game of Life

CF 1349C - Orac and Game of Life Rating: 2000 Tags: dfs and similar, graphs, implementation, shortest paths Solve time: 12m 36s Verified: yes Solution Problem Understanding The grid evolves in discrete time. Each cell has one of two colors and updates simultaneously each step based only on its four neighbors. A cell looks at the current state. If none of its neighbors share its color, it stays unchanged. If...

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Codeforces Round 641 (Div. 1)

Codeforces Round 641 (Div. 1) Type: Div. 1 | Problems: 3 | Verified: 3/3 | Rating range: 2000-3100 | Time: 17m 44s Problem Name Rating Tags Solve Time Verified B Orac and Medians 2000 constructive-algorithms, greedy, math 2m 39s ✓ C Orac and Game of Life 2000 dfs-and-similar, graphs, implementation 12m 36s ✓ F1 Slime and Sequences (Easy Version) 3100 dp, fft, math 2m 29s ✓

Practice › Codeforces Solutions › Codeforces Round 640 (Div. 4) ›

CF 1352F - Binary String Reconstruction

CF 1352F - Binary String Reconstruction Rating: 1500 Tags: constructive algorithms, dfs and similar, math Solve time: 16m 52s Verified: no Solution Problem Understanding We are asked to reconstruct a binary string given the counts of its consecutive pairs grouped by how many ones they contain. The input provides three integers: $n_0$ is the number of adjacent pairs "00", $n_1$ counts pairs with exactly one '1' ("01" or "10"), and...

Practice › Codeforces Solutions › Codeforces Round 647 (Div. 1) - Thanks, Algo Muse! ›

CF 1361E - James and the Chase

CF 1361E - James and the Chase Rating: 3000 Tags: dfs and similar, graphs, probabilities, trees Solve time: 2m 53s Verified: no Solution Correct Solution for TAOCP 4.6.1.24 The exercise asks for a direct algebraic simplification of two displayed identities involving content and primitive part of polynomials over a unique factorization domain $S$. The goal is not to introduce new structural theorems, but to rewrite the given expressions until they...

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CF 1375G - Tree Modification

CF 1375G - Tree Modification Rating: 2800 Tags: brute force, constructive algorithms, dfs and similar, graph matchings, graphs, trees Solve time: 2m 29s Verified: no Solution Setup Let $N\ge 1$ be fixed. An $m$-survivor is a positive integer all of whose prime factors exceed $m$. Let $$ f(x,m)=#{n\le x:\text{$n$ is an $m$-survivor}}, $$ and let $$ f_k(x,m)=#{n\le x:\text{$n$ is an $m$-survivor having exactly $k$ prime factors}}, $$ where prime factors...

Practice › Codeforces Solutions › Codeforces Round 663 (Div. 2) ›

CF 1391E - Pairs of Pairs

CF 1391E - Pairs of Pairs Rating: 2600 Tags: constructive algorithms, dfs and similar, graphs, greedy, trees Solve time: 2m 30s Verified: no Solution Problem Understanding We are given a connected undirected graph, and the task is not to compute a classical graph property, but to construct one of two global structures that are guaranteed to exist. The first possible output is a simple path that visits at least half...

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CF 1392G - Omkar and Pies

CF 1392G - Omkar and Pies Rating: 2900 Tags: bitmasks, dfs and similar, dp, math, shortest paths Solve time: 1m 39s Verified: yes Solution Problem Understanding We are given a very small binary “target state” of size $k \le 20$, representing pies placed in fixed positions. We also have an initial configuration of those pies and a desired configuration. There is a long sequence of operations, each operation being a...

Practice › Codeforces Solutions › Codeforces Round 662 (Div. 2) ›

CF 1393D - Rarity and New Dress

CF 1393D - Rarity and New Dress Rating: 2100 Tags: dfs and similar, dp, implementation, shortest paths Solve time: 1m 22s Verified: yes Solution Problem Understanding We are given a grid of characters where each cell represents a colored tile. From this grid we want to count how many “valid dress patterns” exist. A valid pattern is a rhombus shape whose sides are tilted at 45 degrees relative to the...

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Codeforces Round 664 (Div. 1)

Codeforces Round 664 (Div. 1) Type: Div. 1 | Problems: 5 | Verified: 1/5 | Rating range: 1800-3500 | Time: 20m 59s Problem Name Rating Tags Solve Time Verified A Boboniu Chats with Du 1800 dp, greedy, sortings 5m 19s ✗ B Boboniu Walks on Graph 2300 brute-force, dfs-and-similar, graphs 8m 53s ✗ C Boboniu and String 2600 binary-search, geometry, ternary-search 2m 5s ✓ D Boboniu and Jianghu 2800 dp,...

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CF 1394B - Boboniu Walks on Graph

CF 1394B - Boboniu Walks on Graph Rating: 2300 Tags: brute force, dfs and similar, graphs, hashing Solve time: 8m 53s Verified: no Solution Ah, now the bug is about the order in which the pairs are generated . The input is: 3 3 2 2 and the expected output is: 2 2 1 2 1 3 2 3 3 3 3 2 3 1 2 1 1 1 The...

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Codeforces Round 639 (Div. 1)

Codeforces Round 639 (Div. 1) Div. 1 | 6 problems | 1/6 verified | Difficulty 1600-3200 | 25m 47s # Problem Rating Tags Accepted Time ✓ A Hilbert's Hotel 1600 math, number-theory, sortings 16,502 5m 20s B Monopole Magnets 2000 constructive-algorithms, dfs-and-similar, dsu 6,353 2m 16s ✓ C Quantifier Question 2600 dfs-and-similar, dp, graphs 1,979 3m 29s D R\u00e9sum\u00e9 Review 2700 binary-search, greedy, math 1,292 3m 49s E Train Tracks...

Practice › Codeforces Solutions › Codeforces Round 666 (Div. 1) ›

CF 1396E - Distance Matching

CF 1396E - Distance Matching Rating: 3200 Tags: constructive algorithms, dfs and similar, trees Solve time: 2m 22s Verified: no Solution Problem Understanding We are given a tree with an even number of nodes and an integer $k$. From this tree, we can construct a complete graph where each node represents a vertex from the tree and the weight of an edge between any two vertices is the distance between...

Practice › Codeforces Solutions › Codeforces Round 661 (Div. 3) ›

CF 1399E1 - Weights Division (easy version)

CF 1399E1 - Weights Division (easy version) Rating: 2000 Tags: data structures, dfs and similar, greedy, trees Solve time: 7m 46s Verified: no Solution Thanks - now we can carefully diagnose this. The crash happens here: u, v = map(int, input().split()) with the error: ValueError: not enough values to unpack (expected 2, got 1) Step 1: Examine the input structure The input is: 3 4 1 2 2 3 3...

Practice › Codeforces Solutions › Codeforces Round 661 (Div. 3) ›

CF 1399E2 - Weights Division (hard version)

CF 1399E2 - Weights Division (hard version) Rating: 2200 Tags: binary search, dfs and similar, greedy, sortings, trees, two pointers Solve time: 2m 22s Verified: no Solution Problem Understanding We are given a tree rooted at vertex 1, where each edge has a weight and an associated cost of either 1 or 2 coins. The weight of a path from the root to a leaf is the sum of the...

Practice › Codeforces Solutions › Educational Codeforces Round 94 (Rated for Div. 2) ›

CF 1400F - x-prime Substrings

CF 1400F - x-prime Substrings Rating: 2800 Tags: brute force, dfs and similar, dp, string suffix structures, strings Solve time: 1m 28s Verified: no Solution Problem Understanding We are given a digit string and a small integer $x$. Any contiguous piece of the string has a weight equal to the sum of its digits. Among those substrings whose sum is exactly $x$, some are “dangerous” because they contain an internal...

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Codeforces Round 665 (Div. 2)

Codeforces Round 665 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 3/6 | Rating range: 900-2400 | Time: 24m 18s Problem Name Rating Tags Solve Time Verified A Distance and Axis 900 constructive-algorithms, math 1m 35s ✓ B Ternary Sequence 1100 constructive-algorithms, greedy, math 1m 35s ✓ C Mere Array 1300 constructive-algorithms, math, number-theory 9m 14s ✓ D Maximum Distributed Tree 1800 dfs-and-similar, dp, greedy 7m 36s ✗...

Practice › Codeforces Solutions › Codeforces Round 665 (Div. 2) ›

CF 1401D - Maximum Distributed Tree

CF 1401D - Maximum Distributed Tree Rating: 1800 Tags: dfs and similar, dp, greedy, implementation, math, number theory, sortings, trees Solve time: 7m 36s Verified: no Solution Got it. Let’s go careful step by step . 1. Understanding the problem The input is: 5 1 3 3 6 5 1 5 3 3 3 6 5 2 1 4 1 2 3 4 2 The first line 5 is the...

Practice › Codeforces Solutions › Central-European Olympiad in Informatics, CEOI 2020, Day 1 (IOI, Unofficial Mirror Contest, Unrated) ›

CF 1402C - Star Trek

CF 1402C - Star Trek Rating: 2600 Tags: *special, combinatorics, dfs and similar, dp, games, graphs, matrices, trees Solve time: 1m 26s Verified: yes Solution Problem Understanding We are given a tree of $N$ planets. Each universe contains an identical copy of this tree, so every universe has the same internal structure and the same $N$ nodes connected by $N-1$ undirected edges. There are $D+1$ universes indexed from $0$ to...

Practice › Codeforces Solutions › Central-European Olympiad in Informatics, CEOI 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated) ›

CF 1403B - Spring cleaning

CF 1403B - Spring cleaning Rating: 2300 Tags: *special, data structures, dfs and similar, graphs, trees Solve time: 14m 30s Verified: no Solution Problem Understanding We are given a tree with N nodes, connected by N-1 edges. Each node may be a leaf, defined as a node with exactly one edge. Cleaning the tree involves selecting two different leaves and marking all edges along the shortest path between them as...

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Codeforces Round 630 (Div. 2)

Codeforces Round 630 (Div. 2) Div. 2 | 5 problems | 3/5 verified | Difficulty 1400-3100 | 13m 43s # Problem Rating Tags Accepted Time ✓ B Composite Coloring 1400 brute-force, constructive-algorithms, greedy 18,950 1m 55s C K-Complete Word 1500 dfs-and-similar, dsu, greedy 20,851 2m 56s ✓ E Height All the Same 2100 combinatorics, constructive-algorithms, math 4,311 2m 29s ✓ F Independent Set 2500 dfs-and-similar, dp, trees 1,128 1m 58s...

Practice › Codeforces Solutions › Codeforces Round 670 (Div. 2) ›

CF 1406C - Link Cut Centroids

CF 1406C - Link Cut Centroids Rating: 1700 Tags: constructive algorithms, dfs and similar, graphs, trees Solve time: 8m 12s Verified: no Solution The issue is not actually with the algorithm. The output shown as: means the program produced no output at all. That indicates an implementation problem, not a mathematical one. Looking at the previous code, the sample test harness contained: def run(inp: str) -> str: sys.stdin = io.StringIO(inp)...

Practice › Codeforces Solutions › Codeforces Round 669 (Div. 2) ›

CF 1407E - Egor in the Republic of Dagestan

CF 1407E - Egor in the Republic of Dagestan Rating: 2500 Tags: constructive algorithms, dfs and similar, dp, graphs, greedy, shortest paths Solve time: 1m 47s Verified: no Solution Problem Understanding We are asked to control Egor's travel through a directed graph of cities connected by roads of two types: night roads and morning roads. Each city can be assigned a color, black (night) or white (morning). Egor can leave...

Practice › Codeforces Solutions › Codeforces Round 671 (Div. 2) ›

CF 1419F - Rain of Fire

CF 1419F - Rain of Fire Rating: 2800 Tags: binary search, data structures, dfs and similar, dsu, graphs, implementation Solve time: 1m 42s Verified: no Solution Problem Understanding Fix a value t . Brimstone may wait at any detachment for an arbitrary amount of time. When he decides to move, he chooses one of the four axis directions and keeps moving until he reaches the first detachment lying on that...

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Educational Codeforces Round 82 (Rated for Div. 2)

Educational Codeforces Round 82 (Rated for Div. 2) Div. 2 | 6 problems | 2/6 verified | Difficulty 800-2800 | 21m 13s # Problem Rating Tags Accepted Time ✓ A Erasing Zeroes 800 implementation, strings 36,691 1m 49s ✓ B National Project 1400 math 16,802 3m 33s C Perfect Keyboard 1600 dfs-and-similar, greedy, implementation 12,857 2m 41s D Fill The Bag 1900 bitmasks, greedy 7,706 6m 48s ✓ F Number...

Practice › Codeforces Solutions › Educational Codeforces Round 96 (Rated for Div. 2) ›

CF 1430G - Yet Another DAG Problem

CF 1430G - Yet Another DAG Problem Rating: 2600 Tags: bitmasks, dfs and similar, dp, flows, graphs, math Solve time: 2m 40s Verified: no Solution The key issue is that this is a constructive problem . The output shown in the statement is only one valid sequence of operations, not the unique correct output. Your program's output is different from the sample output, but that does not mean it is...

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Kotlin Heroes: Episode 3

Kotlin Heroes: Episode 3 Kotlin | 9 problems | 1/9 verified | Difficulty - | 32m 16s # Problem Rating Tags Accepted Time ✓ A Likes Display *special, implementation 958 1m 57s ✓ B Cartoons *special, implementation, sortings 433 3m 5s C Dream Team *special, greedy 414 3m 24s D Bonus Distribution *special, binary-search, greedy 274 3m 37s E Modernization of Treeland *special, dfs-and-similar, trees 218 3m 35s F Movie...

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Codeforces Round 677 (Div. 3)

Codeforces Round 677 (Div. 3) Type: Div. 3 | Problems: 7 | Verified: 3/7 | Rating range: 800-2100 | Time: 19m 11s Problem Name Rating Tags Solve Time Verified A Boring Apartments 800 implementation, math 2m 40s ✗ B Yet Another Bookshelf 800 greedy, implementation 1m 30s ✓ C Dominant Piranha 900 constructive-algorithms, greedy 8m 25s ✗ D Districts Connection 1200 constructive-algorithms, dfs-and-similar 1m 28s ✗ E Two Round Dances...

Practice › Codeforces Solutions › Codeforces Round 677 (Div. 3) ›

CF 1433D - Districts Connection

CF 1433D - Districts Connection Rating: 1200 Tags: constructive algorithms, dfs and similar Solve time: 1m 28s Verified: no Solution Problem Understanding We are given several independent scenarios. In each scenario there are $n$ districts, and each district belongs to some gang identified by an integer label. Our task is to construct a set of exactly $n-1$ undirected roads so that all districts become connected as a single connected component,...

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Codeforces Round 678 (Div. 2)

Codeforces Round 678 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 3/6 | Rating range: 800-2800 | Time: 13m 27s Problem Name Rating Tags Solve Time Verified A Reorder 800 math 3m 26s ✓ B Prime Square 900 constructive-algorithms, math 2m 44s ✗ C Binary Search 1500 binary-search, combinatorics 1m 35s ✓ D Bandit in a City 1900 binary-search, dfs-and-similar, graphs 1m 33s ✓ E Complicated Computations 2400...

Practice › Codeforces Solutions › Codeforces Round 678 (Div. 2) ›

CF 1436D - Bandit in a City

CF 1436D - Bandit in a City Rating: 1900 Tags: binary search, dfs and similar, graphs, greedy, trees Solve time: 1m 33s Verified: yes Solution Problem Understanding We are given a rooted tree with node 1 acting as the starting point of a bandit. Every edge is directed away from the root in such a way that from node 1, every other node is reachable, so the structure is effectively...

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Codeforces Round 615 (Div. 3)

Codeforces Round 615 (Div. 3) Div. 3 | 4 problems | 3/4 verified | Difficulty 800-2000 | 11m 4s # Problem Rating Tags Accepted Time ✓ A Collecting Coins 800 math 53,415 1m 49s ✓ C Product of Three Numbers 1300 greedy, math, number-theory 46,245 2m 23s ✓ E Obtain a Permutation 1900 greedy, implementation, math 5,177 1m 54s ✓ F Three Paths on a Tree 2000 dfs-and-similar, dp, greedy...

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Codeforces Round 614 (Div. 1)

Codeforces Round 614 (Div. 1) Div. 1 | 5 problems | 2/5 verified | Difficulty 1400-3500 | 17m 14s # Problem Rating Tags Accepted Time ✓ A NEKO's Maze Game 1400 data-structures, dsu, implementation 13,871 1m 55s ✓ C Xenon's Attack on the Gangs 2300 combinatorics, dfs-and-similar, dp 2,252 1m 10s D Chaotic V. 2700 dp, graphs, greedy 971 7m 22s E Rin and The Unknown Flower 3500 constructive-algorithms, greedy,...

Practice › Codeforces Solutions › Codeforces Round 681 (Div. 1, based on VK Cup 2019-2020 - Final) ›

CF 1442C - Graph Transpositions

CF 1442C - Graph Transpositions Rating: 2400 Tags: dfs and similar, graphs, greedy, shortest paths Solve time: 6m 37s Verified: no Solution Thank you. Now I see exactly why the previous code is producing the wrong output. Let’s go carefully. Input 3 10 4 12 6 179 822 Expected output 10 4 179 Actual output 10 12 179 Diagnosis The code currently reads each line and assigns: a, b =...

Practice › Codeforces Solutions › Codeforces Round 681 (Div. 1, based on VK Cup 2019-2020 - Final) ›

CF 1442E - Black, White and Grey Tree

CF 1442E - Black, White and Grey Tree Rating: 3000 Tags: binary search, constructive algorithms, dfs and similar, dp, greedy, trees Solve time: 1m 48s Verified: no Solution Problem Understanding We are given a tree in which each node is coloured white, black, or grey. The goal is to remove all nodes in the minimum number of operations, where in each operation we select a connected component of nodes to...

Practice › Codeforces Solutions › Codeforces Round 680 (Div. 1, based on Moscow Team Olympiad) ›

CF 1444C - Team-Building

CF 1444C - Team-Building Rating: 2500 Tags: data structures, dfs and similar, dsu, graphs Solve time: 5m 14s Verified: yes Solution The root of the discrepancy lies in floating-point precision , not in the algorithm itself. On the input provided, the distance we want is exactly $$\frac{\sqrt{2}}{2} \approx 0.7071067811865476$$ However, the expected output in the sample is 0.707106780737 , which is slightly lower. This difference arises because the official problem...

Practice › Codeforces Solutions › Codeforces Round 680 (Div. 1, based on Moscow Team Olympiad) ›

CF 1444E - Finding the Vertex

CF 1444E - Finding the Vertex Rating: 3500 Tags: brute force, dfs and similar, dp, interactive, trees Solve time: 1m 39s Verified: no Solution Problem Understanding We are given a tree with up to 100 vertices, and somewhere inside this tree there is a hidden “special” vertex. We do not know which one it is. The only way to gain information is to query an edge, and the response tells...

Practice › Codeforces Solutions › Codeforces Round 683 (Div. 1, by Meet IT) ›

CF 1446E - Long Recovery

CF 1446E - Long Recovery Rating: 3500 Tags: constructive algorithms, dfs and similar Solve time: 2m 3s Verified: no Solution Problem Understanding The system describes an infinite triangular grid where every cell has exactly three neighbors. The geometry is unusual compared to a square grid because adjacency depends on the parity of the x-coordinate, which flips one of the diagonal connections. Despite the infinite nature, only a finite set of...

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Codeforces Round 612 (Div. 1)

Codeforces Round 612 (Div. 1) Div. 1 | 5 problems | 1/5 verified | Difficulty 1800-3200 | 20m 52s # Problem Rating Tags Accepted Time ✓ A Garland 1800 dp, greedy, sortings 9,643 2m 42s ✓ B Numbers on Tree 1800 constructive-algorithms, data-structures, dfs-and-similar 5,467 5m 21s C1 Madhouse (Easy version) 2400 brute-force, constructive-algorithms, interactive 1,579 4m 5s C2 Madhouse (Hard version) 2800 brute-force, constructive-algorithms, hashing 745 6m 2s E...

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CF 1450E - Capitalism

CF 1450E - Capitalism Rating: 2700 Tags: constructive algorithms, dfs and similar, graphs, shortest paths Solve time: 1m 59s Verified: no Solution Problem Understanding We are given a connected undirected graph where each vertex represents a person and each edge represents a friendship. The task is not to assign values arbitrarily, but to assign an integer income to every vertex so that every friendship satisfies a very rigid rule: along...

Practice › Codeforces Solutions › Educational Codeforces Round 98 (Rated for Div. 2) ›

CF 1452G - Game On Tree

CF 1452G - Game On Tree Rating: 2700 Tags: data structures, dfs and similar, greedy, trees Solve time: 10m 51s Verified: no Solution I see exactly what went wrong in the previous implementation. The problem is subtle: the “all equal” case [1, 1, 1] fails because the formula incorrectly tries to round the sum to the next multiple of n-1 even when the current sum is already enough to satisfy...

Practice › Codeforces Solutions › Codeforces Round 688 (Div. 2) ›

CF 1453E - Dog Snacks

CF 1453E - Dog Snacks Rating: 2300 Tags: binary search, dfs and similar, dp, greedy, trees Solve time: 1m 48s Verified: no Solution Problem Understanding We are given a tree with $n$ vertices, each vertex containing a snack. A dog starts at node $1$ and repeatedly moves until it has eaten all snacks, then must return to node $1$. Movement is constrained by a parameter $k$: at every step the...

Practice › Codeforces Solutions › Codeforces Round 686 (Div. 3) ›

CF 1454E - Number of Simple Paths

CF 1454E - Number of Simple Paths Rating: 2000 Tags: combinatorics, dfs and similar, graphs, trees Solve time: 1m 47s Verified: no Solution Problem Understanding We are given a connected undirected graph where the number of edges equals the number of vertices. This immediately implies the structure is almost a tree, except for exactly one extra edge that creates a single cycle somewhere in the graph. The task is to...

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Codeforces Round 607 (Div. 1)

Codeforces Round 607 (Div. 1) Div. 1 | 6 problems | 2/6 verified | Difficulty 1700-3400 | 35m 2s # Problem Rating Tags Accepted Time ✓ A Cut and Paste 1700 implementation, math 5,842 2m 8s ✓ B Beingawesomeism 1800 implementation, math 4,203 6m 37s C Jeremy Bearimy 2000 dfs-and-similar, graphs, greedy 3,038 11m 16s D Miss Punyverse 2500 dp, greedy, trees 1,230 6m 38s E Kirchhoff's Current Loss 2900...

Practice › Codeforces Solutions › Educational Codeforces Round 100 (Rated for Div. 2) ›

CF 1463E - Plan of Lectures

CF 1463E - Plan of Lectures Rating: 2400 Tags: constructive algorithms, dfs and similar, dsu, graphs, implementation, sortings, trees Solve time: 2m 25s Verified: no Solution Problem Understanding We have a teacher, Ivan, who needs to schedule lectures on n different topics. Each topic has at most one prerequisite, meaning he cannot lecture on a topic before its prerequisite. One topic has no prerequisite. The task is to arrange the...

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CF 1466F - Euclid's nightmare

CF 1466F - Euclid's nightmare Rating: 2100 Tags: bitmasks, dfs and similar, dsu, graphs, greedy, math, sortings Solve time: 1m 53s Verified: yes Solution Problem Understanding We are given a collection of binary vectors of length $m$, where each vector contains at most two positions set to 1. We can combine vectors using XOR, since addition over $\mathbb{Z}_2$ is exactly bitwise XOR. From all possible XORs of subsets of these...

Practice › Codeforces Solutions › Codeforces Round 695 (Div. 2) ›

CF 1467E - Distinctive Roots in a Tree

CF 1467E - Distinctive Roots in a Tree Rating: 2500 Tags: data structures, dfs and similar, dp, trees Solve time: 2m 58s Verified: no Solution Problem Understanding We are given a tree whose vertices carry values. We may choose any vertex as the root. Once a root is fixed, every simple path starting at the root and ending at some descendant becomes a root-to-node path. A root is called distinctive...

Practice › Codeforces Solutions › Codeforces Round 694 (Div. 1) ›

CF 1470D - Strange Housing

CF 1470D - Strange Housing Rating: 2200 Tags: constructive algorithms, dfs and similar, graph matchings, graphs, greedy Solve time: 2m 20s Verified: no Solution Problem Understanding We are given an undirected graph where vertices represent houses and edges represent underground passages. We must choose a subset of vertices to place teachers in. Once the selection is made, all edges whose endpoints are both unchosen are removed. Every other edge remains....

Practice › Codeforces Solutions › Codeforces Round 693 (Div. 3) ›

CF 1472G - Moving to the Capital

CF 1472G - Moving to the Capital Rating: 2100 Tags: dfs and similar, dp, graphs, shortest paths Solve time: 11m 29s Verified: no Solution Problem Understanding We are given a directed graph whose vertices are cities and whose root is city 1, the capital. For every city $v$, define $d[v]$ as the shortest path length from city 1 to $v$. These distances are fixed and known implicitly from the graph....

Practice › Codeforces Solutions › Educational Codeforces Round 103 (Rated for Div. 2) ›

CF 1476E - Pattern Matching

CF 1476E - Pattern Matching Rating: 2300 Tags: bitmasks, data structures, dfs and similar, graphs, hashing, sortings, strings Solve time: 2m 53s Verified: no Solution I can't reliably diagnose this one from the sample alone because the sample input/output pair does not identify the problem. The behavior strongly suggests that the Python program being tested is actually a solution for a completely different problem: Your input contains 3 test cases....

Practice › Codeforces Solutions › Educational Codeforces Round 103 (Rated for Div. 2) ›

CF 1476D - Journey

CF 1476D - Journey Rating: 1700 Tags: dfs and similar, dp, dsu, implementation Solve time: 3m 17s Verified: no Solution Problem Understanding We are given a chain of cities numbered from 0 to $n$, connected linearly by $n$ roads. Each road has a direction, either left (from city $i$ to $i-1$) or right (from $i-1$ to $i$). A traveler wants to start from some city and visit as many distinct...

Practice › Codeforces Solutions › Codeforces Round 698 (Div. 1) ›

CF 1477D - Nezzar and Hidden Permutations

CF 1477D - Nezzar and Hidden Permutations Rating: 2800 Tags: constructive algorithms, dfs and similar, graphs Solve time: 3m 22s Verified: no Solution Problem Understanding We are given an undirected graph on vertices 1..n . Every pair (l, r) chosen by Nanako becomes an edge of this graph. Nezzar must construct two permutations p and q of 1..n . For every edge (u, v) , the differences p[u] - p[v]...

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Codeforces Round 748 (Div. 3)

Codeforces Round 748 (Div. 3) Div. 3 | 8 problems | 5/8 verified | Difficulty 800-2200 | 21m 56s # Problem Rating Tags Accepted Time ✓ A Elections 800 math 41,525 1m 48s ✓ B Make it Divisible by 25 900 dfs-and-similar, dp, greedy 40,606 2m 52s ✓ C Save More Mice 1000 binary-search, greedy 27,878 2m 45s D1 All are Same 1100 math, number-theory 21,797 1m 34s ✓ D2...

Practice › Codeforces Solutions › Codeforces Round 701 (Div. 2) ›

CF 1485E - Move and Swap

CF 1485E - Move and Swap Rating: 2500 Tags: dfs and similar, dp, greedy, trees Solve time: 2m 54s Verified: no Solution Problem Understanding We are given a rooted tree where every root-to-leaf path has the same length. Each non-root vertex has a value, while the root has no value attached. Two tokens start together at the root. One token, which we can think of as the red one, must...

Practice › Codeforces Solutions › Codeforces Round 703 (Div. 2) ›

CF 1486F - Pairs of Paths

CF 1486F - Pairs of Paths Rating: 2600 Tags: combinatorics, data structures, dfs and similar, dp, trees Solve time: 3m 12s Verified: no Solution Problem Understanding We are given a tree with n vertices, meaning a connected graph with n-1 edges and no cycles. Along with the tree, we are given m paths, each specified by its two endpoints u and v . The path is implicitly the unique sequence...

Practice › Codeforces Solutions › Educational Codeforces Round 104 (Rated for Div. 2) ›

CF 1487C - Minimum Ties

CF 1487C - Minimum Ties Rating: 1500 Tags: brute force, constructive algorithms, dfs and similar, graphs, greedy, implementation, math Solve time: 6m 5s Verified: no Solution Problem Understanding We are asked to design the results of a round-robin football tournament so that every team ends up with the same number of points. There are $n$ teams, and each pair plays exactly once. Each match can either end in a tie...

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Codeforces Round 702 (Div. 3)

Codeforces Round 702 (Div. 3) Type: Div. 3 | Problems: 7 | Verified: 5/7 | Rating range: 800-1900 | Time: 21m 17s Problem Name Rating Tags Solve Time Verified A Dense Array 800 greedy, math 1m 58s ✓ B Balanced Remainders 1000 brute-force, constructive-algorithms, math 5m 10s ✓ C Sum of Cubes 1100 binary-search, brute-force, math 2m 30s ✓ D Permutation Transformation 1200 dfs-and-similar, divide-and-conquer, implementation 2m 32s ✗ E...

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CF 1490D - Permutation Transformation

CF 1490D - Permutation Transformation Rating: 1200 Tags: dfs and similar, divide and conquer, implementation Solve time: 2m 32s Verified: no Solution Problem Understanding We are given a permutation of length $n$, which is an array containing every integer from 1 to $n$ exactly once. The task is to view this permutation as a way to construct a binary tree: the root is the largest element, the elements to the...

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CF 1491E - Fib-tree

CF 1491E - Fib-tree Rating: 2400 Tags: brute force, dfs and similar, divide and conquer, number theory, trees Solve time: 1m 35s Verified: yes Solution Problem Understanding We are given a tree with $n$ vertices, and we want to determine whether it is a Fib-tree. A Fib-tree is a tree whose size equals some Fibonacci number $F_k$, and it either consists of a single vertex or can be split into...

Practice › Codeforces Solutions › Codeforces Round 704 (Div. 2) ›

CF 1492E - Almost Fault-Tolerant Database

CF 1492E - Almost Fault-Tolerant Database Rating: 2500 Tags: brute force, constructive algorithms, dfs and similar, greedy, implementation Solve time: 3m 4s Verified: no Solution I can't reliably diagnose this one from the sample alone because the sample input/output pair does not identify the problem. The behavior strongly suggests that the Python program being tested is actually a solution for a completely different problem: Your input contains 3 test cases....

Practice › Codeforces Solutions › Educational Codeforces Round 105 (Rated for Div. 2) ›

CF 1494F - Delete The Edges

CF 1494F - Delete The Edges Rating: 2900 Tags: brute force, constructive algorithms, dfs and similar, graphs, implementation Solve time: 3m 25s Verified: yes Solution Problem Understanding We are given a connected undirected graph with n vertices and m edges. The task is to remove all edges by walking along them. Initially, walking along an edge destroys it. At most once, we can activate a mode shift. After the mode...

Practice › Codeforces Solutions › Educational Codeforces Round 105 (Rated for Div. 2) ›

CF 1494D - Dogeforces

CF 1494D - Dogeforces Rating: 2300 Tags: constructive algorithms, data structures, dfs and similar, divide and conquer, dsu, greedy, sortings, trees Solve time: 2m 42s Verified: no Solution Problem Understanding We are asked to reconstruct a company hierarchy from partial salary information. Specifically, we know the salaries of all the lowest-level employees and, for every pair of them, the salary of their lowest common supervisor. The hierarchy is a tree...

Practice › Codeforces Solutions › Codeforces Round 706 (Div. 1) ›

CF 1495D - BFS Trees

CF 1495D - BFS Trees Rating: 2600 Tags: combinatorics, dfs and similar, graphs, math, shortest paths, trees Solve time: 1m 16s Verified: no Solution Problem Understanding We are asked to count, for every pair of vertices $i, j$ in an undirected connected graph, the number of spanning trees that simultaneously behave as BFS trees rooted at both $i$ and $j$. A BFS tree rooted at $s$ preserves the shortest distances...

Practice › Codeforces Solutions › CodeCraft-21 and Codeforces Round 711 (Div. 2) ›

CF 1498F - Christmas Game

CF 1498F - Christmas Game Rating: 2500 Tags: bitmasks, data structures, dfs and similar, dp, games, math, trees Solve time: 5m 30s Verified: no Solution Problem Understanding We are asked to analyze a two-player game on a tree. Each node of the tree contains a certain number of presents, and players take turns moving presents from nodes to their $k$-th ancestor. The player who cannot make a move loses. The...

Practice › Codeforces Solutions › CodeCraft-21 and Codeforces Round 711 (Div. 2) ›

CF 1498D - Bananas in a Microwave

CF 1498D - Bananas in a Microwave Rating: 2200 Tags: dfs and similar, dp, graphs, implementation Solve time: 4m 11s Verified: no Solution Problem Understanding We are simulating a process that builds up a number starting from zero. At each of $n$ time steps, we are given an operation that can be partially repeated. Each operation comes with a limit $y_i$, and we choose how many times to apply it,...

Practice › Codeforces Solutions › Codeforces Round 715 (Div. 1) ›

CF 1508E - Tree Calendar

CF 1508E - Tree Calendar Rating: 3100 Tags: brute force, constructive algorithms, data structures, dfs and similar, sortings, trees Solve time: 2m 19s Verified: no Solution Problem Understanding We are given a rooted directed tree. Every edge points from a parent to a child. Originally, each vertex contained a label from 1 to n , and those labels formed some valid DFS preorder numbering of the tree. In a DFS...

Practice › Codeforces Solutions › Codeforces Round 715 (Div. 1) ›

CF 1508C - Complete the MST

CF 1508C - Complete the MST Rating: 2500 Tags: bitmasks, brute force, data structures, dfs and similar, dsu, graphs, greedy, trees Solve time: 2m 41s Verified: no Solution Problem Understanding We are working with a complete undirected graph, but only some edges come with fixed weights. Every missing edge can be assigned any non-negative integer weight we want. After assigning all missing weights, two conditions must hold simultaneously. First, if...

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2020-2021 ICPC, NERC, Northern Eurasia Onsite (Unrated, Online Mirror, ICPC Rules, Teams Preferred)

2020-2021 ICPC, NERC, Northern Eurasia Onsite (Unrated, Online Mirror, ICPC Rules, Teams Preferred) Type: ICPC/IOI | Problems: 11 | Verified: 5/11 | Rating range: 1200-3200 | Time: 49m 4s Problem Name Rating Tags Solve Time Verified A ASCII Automata Art 3100 - 1m 16s ✗ B Button Lock 2600 flows, graph-matchings, graphs 3m 7s ✓ C Cactus Not Enough 2900 dfs-and-similar, graph-matchings, graphs 3m 19s ✗ D Digits 2100 dp,...

Practice › Codeforces Solutions › 2020-2021 ICPC, NERC, Northern Eurasia Onsite (Unrated, Online Mirror, ICPC Rules, Teams Preferred) ›

CF 1510C - Cactus Not Enough

CF 1510C - Cactus Not Enough Rating: 2900 Tags: dfs and similar, graph matchings, graphs Solve time: 3m 19s Verified: no Solution Problem Understanding The problem gives us a cactus graph, which is a connected undirected graph where each edge belongs to at most one simple cycle. You can think of a cactus as a tree that allows some cycles, but never overlapping cycles. The input represents these cacti in...

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CF 1515G - Phoenix and Odometers

CF 1515G - Phoenix and Odometers Rating: 2700 Tags: dfs and similar, graphs, math, number theory Solve time: 1m 31s Verified: yes Solution Problem Understanding We are given a directed graph representing intersections in a city and one-way roads between them, each with a positive integer length. A set of cars starts at specific intersections, each with an odometer that begins at a number s and wraps around to zero...

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CF 1515F - Phoenix and Earthquake

CF 1515F - Phoenix and Earthquake Rating: 2600 Tags: constructive algorithms, dfs and similar, dsu, graphs, greedy, trees Solve time: 2m 56s Verified: no Solution Problem Understanding The problem describes a scenario where a country’s road network has been destroyed by an earthquake, leaving n cities and m roads in a disconnected state. Each city starts with a certain amount of asphalt, and building a road consumes a fixed amount...

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Contest 2050 and Codeforces Round 718 (Div. 1 + Div. 2)

Contest 2050 and Codeforces Round 718 (Div. 1 + Div. 2) Type: Div. 1+2 | Problems: 8 | Verified: 4/8 | Rating range: 800-3500 | Time: 18m 5s Problem Name Rating Tags Solve Time Verified A Sum of 2050 800 greedy, math 2m 6s ✓ B Morning Jogging 1200 constructive-algorithms, greedy, sortings 2m 55s ✗ C Fillomino 2 1400 constructive-algorithms, dfs-and-similar, greedy 2m 17s ✓ D Explorer Space 1800 dp,...

Practice › Codeforces Solutions › Contest 2050 and Codeforces Round 718 (Div. 1 + Div. 2) ›

CF 1517C - Fillomino 2

CF 1517C - Fillomino 2 Rating: 1400 Tags: constructive algorithms, dfs and similar, greedy, implementation Solve time: 2m 17s Verified: yes Solution Problem Understanding We are given an $n \times n$ lower-triangular part of a chessboard, where only the diagonal and the cells below it matter. On the main diagonal, each cell contains a distinct integer from 1 to $n$, forming a permutation. The task is to partition the cells...

Practice › Codeforces Solutions › Educational Codeforces Round 108 (Rated for Div. 2) ›

CF 1519F - Chests and Keys

CF 1519F - Chests and Keys Rating: 3200 Tags: bitmasks, brute force, dfs and similar, dp, flows Solve time: 2m 43s Verified: no Solution Solution Method 1b already provides the key idea. If $(u_m\ldots u_1u_0)_3$ is a ternary integer, its decimal value is obtained from the nested form $$(\cdots((u_m\cdot3+u_{m-1})\cdot3+u_{m-2})\cdots)\cdot3+u_0.$$ For pencil-and-paper work this means: Start with the leading digit. Repeatedly multiply the current result by $3$ and add the next...

Practice › Codeforces Solutions › Educational Codeforces Round 108 (Rated for Div. 2) ›

CF 1519E - Off by One

CF 1519E - Off by One Rating: 2700 Tags: constructive algorithms, dfs and similar, geometry, graphs, sortings, trees Solve time: 2m 32s Verified: no Solution Problem Understanding We are given $n$ points in the first quadrant of a plane. Each point is defined by a pair of rational coordinates $(x_i, y_i)$, where $x_i = a_i / b_i$ and $y_i = c_i / d_i$. A move consists of picking two points,...

Practice › Codeforces Solutions › Codeforces Round 719 (Div. 3) ›

CF 1520G - To Go Or Not To Go?

CF 1520G - To Go Or Not To Go? Rating: 2200 Tags: brute force, dfs and similar, graphs, greedy, implementation, shortest paths Solve time: 2m 14s Verified: yes Solution Problem Understanding We are asked to find the minimum time for Dima to travel from the top-left corner of a rectangular city grid to the bottom-right corner. The city is represented as an n × m grid where each cell has...

Practice › Codeforces Solutions ›

Codeforces Round 720 (Div. 2)

Codeforces Round 720 (Div. 2) Type: Div. 2 | Problems: 5 | Verified: 0/5 | Rating range: 1000-2700 | Time: 26m 47s Problem Name Rating Tags Solve Time Verified A Nastia and Nearly Good Numbers 1000 constructive-algorithms, math, number-theory 2m 11s ✗ B Nastia and a Good Array 1300 constructive-algorithms, math, number-theory 4m 34s ✗ C Nastia and a Hidden Permutation 2000 constructive-algorithms, interactive 2m 36s ✗ D Nastia Plays...

Practice › Codeforces Solutions › Codeforces Round 720 (Div. 2) ›

CF 1521D - Nastia Plays with a Tree

CF 1521D - Nastia Plays with a Tree Rating: 2500 Tags: constructive algorithms, data structures, dfs and similar, dp, dsu, greedy, implementation, trees Solve time: 14m 56s Verified: no Solution Problem Understanding We start with a tree, meaning a connected graph with $n$ vertices and exactly $n-1$ edges. Each move allows us to remove one existing edge and insert a new edge between any two vertices. The structure is allowed...

Practice › Codeforces Solutions › Codeforces Round 721 (Div. 2) ›

CF 1527D - MEX Tree

CF 1527D - MEX Tree Rating: 2400 Tags: combinatorics, dfs and similar, implementation, math, trees Solve time: 3m 53s Verified: no Solution Problem Understanding We have a tree whose vertices are labeled with the integers 0 through n - 1 . For every unordered pair of distinct vertices (u, v) , we look at the unique simple path connecting them. The labels appearing on that path form a set of...

Practice › Codeforces Solutions ›

Codeforces Round 722 (Div. 1)

Codeforces Round 722 (Div. 1) Type: Div. 1 | Problems: 6 | Verified: 3/6 | Rating range: 1600-3300 | Time: 26m Problem Name Rating Tags Solve Time Verified A Parsa's Humongous Tree 1600 dfs-and-similar, divide-and-conquer, dp 2m 53s ✗ B Kavi on Pairing Duty 1700 combinatorics, dp, math 11m 8s ✓ C Trees of Tranquillity 2300 data-structures, dfs-and-similar, greedy 3m 12s ✓ D It's a bird! No, it's a plane!...

Practice › Codeforces Solutions › Codeforces Round 722 (Div. 1) ›

CF 1528C - Trees of Tranquillity

CF 1528C - Trees of Tranquillity Rating: 2300 Tags: data structures, dfs and similar, greedy, trees Solve time: 3m 12s Verified: yes Solution Problem Understanding We are given two rooted trees on the same set of vertices 1..n . Both trees are rooted at vertex 1 . From these two trees we define a graph. Two vertices are connected if they satisfy two conditions simultaneously. The first condition says that...

Practice › Codeforces Solutions › Codeforces Round 722 (Div. 1) ›

CF 1528A - Parsa's Humongous Tree

CF 1528A - Parsa's Humongous Tree Rating: 1600 Tags: dfs and similar, divide and conquer, dp, greedy, trees Solve time: 2m 53s Verified: no Solution Problem Understanding We are given a tree with n vertices. On each vertex, there is a range [l_v, r_v] of integers that can be assigned. We need to assign a number a_v to each vertex within its range so that the sum of absolute differences...

Practice › Codeforces Solutions › Codeforces LATOKEN Round 1 (Div. 1 + Div. 2) ›

CF 1534F2 - Falling Sand (Hard Version)

CF 1534F2 - Falling Sand (Hard Version) Rating: 3000 Tags: dfs and similar, dp, graphs, greedy Solve time: 2m 41s Verified: no Solution Problem Understanding We are given a grid representing a vertical board filled with sand blocks. Each cell either contains a block or is empty. There are also target requirements per column: for every column, we want at least a certain number of sand blocks to end up...

Practice › Codeforces Solutions › Codeforces LATOKEN Round 1 (Div. 1 + Div. 2) ›

CF 1534F1 - Falling Sand (Easy Version)

CF 1534F1 - Falling Sand (Easy Version) Rating: 2500 Tags: dfs and similar, graphs, greedy Solve time: 2m 51s Verified: no Solution Problem Understanding We are given a grid of n rows and m columns where each cell either contains a sand block ( # ) or is empty ( . ). Alongside the grid, we are given an array a of length m . In this easy version of...

Practice › Codeforces Solutions › Educational Codeforces Round 110 (Rated for Div. 2) ›

CF 1535D - Playoff Tournament

CF 1535D - Playoff Tournament Rating: 1800 Tags: data structures, dfs and similar, dp, implementation, trees Solve time: 1m 5s Verified: no Solution Correctness The proposed solution does not answer the exercise at all. Exercise 4.3.2.7 asks for a derivation of an alternative form of equation (24) in the Chinese remainder conversion algorithm, followed by a discussion of the computational advantages and disadvantages of storing the constants $$C_j=c_{1j}c_{2j}\cdots c_{j-1,j}\pmod{m_j}$$ instead...

Practice › Codeforces Solutions › Codeforces Round 726 (Div. 2) ›

CF 1537F - Figure Fixing

CF 1537F - Figure Fixing Rating: 2200 Tags: constructive algorithms, dfs and similar, dsu, graphs, greedy, math Solve time: 2m 28s Verified: yes Solution Problem Understanding We are given a connected undirected graph where each node has an initial value and a target value. We can pick any edge and add the same integer to both endpoints. The task is to determine whether there exists a sequence of such operations...

Practice › Codeforces Solutions › Codeforces Global Round 15 ›

CF 1552G - A Serious Referee

CF 1552G - A Serious Referee Rating: 3000 Tags: bitmasks, brute force, dfs and similar, sortings Solve time: 1m 14s Verified: no Solution Problem Understanding We are asked to determine if a specific sequence of partial sorts can guarantee that any array of length $n$ will be fully sorted at the end. The input specifies $n$, the size of the array, and $k$, the number of sorting steps Andrea performs....

Practice › Codeforces Solutions › Codeforces Round 735 (Div. 2) ›

CF 1554E - You

CF 1554E - You Rating: 2600 Tags: dfs and similar, dp, math, number theory Solve time: 2m 39s Verified: yes Solution Problem Understanding We are given a tree with $n$ nodes, which is a connected acyclic graph, and we need to construct sequences by repeatedly erasing nodes. Each time we erase a node, we record in the sequence the number of its remaining neighbors at that moment, then remove the...

Practice › Codeforces Solutions › Codeforces Global Round 16 ›

CF 1566E - Buds Re-hanging

CF 1566E - Buds Re-hanging Rating: 2000 Tags: constructive algorithms, dfs and similar, dp, greedy, trees Solve time: 4m 2s Verified: no Solution Problem Understanding We are given a rooted tree with root at vertex 1. A vertex is a leaf if it has no children. A vertex is a bud if it is not the root, has at least one child, and every one of its children is a...

Practice › Codeforces Solutions › Codeforces Round 742 (Div. 2) ›

CF 1567F - One-Four Overload

CF 1567F - One-Four Overload Rating: 2700 Tags: 2-sat, constructive algorithms, dfs and similar, dsu, graphs, implementation Solve time: 2m 18s Verified: no Solution Problem Understanding We are given a grid of size $n \times m$ where some cells are marked with an X and the rest are unmarked . . The marked cells are never on the boundary of the grid. Our task is to fill every unmarked cell...

Practice › Codeforces Solutions › Educational Codeforces Round 113 (Rated for Div. 2) ›

CF 1569F - Palindromic Hamiltonian Path

CF 1569F - Palindromic Hamiltonian Path Rating: 3000 Tags: brute force, dfs and similar, dp, graphs, hashing Solve time: 1m 18s Verified: yes Solution Problem Understanding We are given a small undirected graph with at most 12 vertices. We want to assign each vertex a letter from a fixed alphabet of size k . Every such assignment produces a labeled graph. The labeling is considered valid if there exists some...

Practice › Codeforces Solutions › Educational Codeforces Round 114 (Rated for Div. 2) ›

CF 1574F - Occurrences

CF 1574F - Occurrences Rating: 2700 Tags: combinatorics, dfs and similar, dp, dsu, fft, graphs Solve time: 2m Verified: no Solution Problem Understanding We are asked to construct a length m array a , where each position can take a value from 1 to k . The twist is that we are given several “pattern arrays” A_i , and these patterns impose constraints on how often they are allowed to...

Practice › Codeforces Solutions › Educational Codeforces Round 114 (Rated for Div. 2) ›

CF 1574D - The Strongest Build

CF 1574D - The Strongest Build Rating: 2000 Tags: binary search, brute force, data structures, dfs and similar, graphs, greedy, hashing, implementation Solve time: 1m 21s Verified: yes Solution Problem Understanding In this problem, we are asked to help Ivan choose the strongest possible hero build from a set of equipment slots, each with multiple items of different strengths. Each slot has its own list of items, already sorted by...

Practice › Codeforces Solutions › COMPFEST 13 - Finals Online Mirror (Unrated, ICPC Rules, Teams Preferred) ›

CF 1575D - Divisible by Twenty-Five

CF 1575D - Divisible by Twenty-Five Rating: 1800 Tags: brute force, dfs and similar, dp Solve time: 2m 1s Verified: yes Solution Problem Understanding We are given a very short string, at most length 8, that represents a partially unknown integer. Some positions contain fixed digits, some contain a wildcard underscore meaning “any digit is allowed here”, and some contain the character X meaning all X positions must share the...

Practice › Codeforces Solutions ›

Technocup 2022 - Elimination Round 3

Technocup 2022 - Elimination Round 3 Type: Special | Problems: 7 | Verified: 3/7 | Rating range: 800-2500 | Time: 19m 11s Problem Name Rating Tags Solve Time Verified A Life of a Flower 800 implementation 3m 37s ✓ B Array Eversion 900 greedy 1m 48s ✓ C Minimize Distance 1300 greedy 8m 35s ✗ D Yet Another Sorting Problem 1900 data-structures, math 1m 30s ✓ E Frequency Queries 2400...

Practice › Codeforces Solutions › Technocup 2022 - Elimination Round 3 ›

CF 1585E - Frequency Queries

CF 1585E - Frequency Queries Rating: 2400 Tags: data structures, dfs and similar, trees Solve time: 2m 9s Verified: no Solution Problem Understanding We are given a rooted tree where every node stores an integer value. The root is fixed at node 1. For each query, we pick a node v and look at all values along the path from v up to the root. This path is treated as...

Practice › Codeforces Solutions › Codeforces Round 746 (Div. 2) ›

CF 1592C - Bakry and Partitioning

CF 1592C - Bakry and Partitioning Rating: 1700 Tags: bitmasks, constructive algorithms, dfs and similar, dp, graphs, trees Solve time: 8m 32s Verified: yes Solution Thank you. Now that we can see the input and expected output, we can deduce exactly what the logic should be. The previous solution printed the raw input values because it never actually implemented the computation - it just parsed and printed n . The...

Practice › Codeforces Solutions › Codeforces Round 746 (Div. 2) ›

CF 1592D - Hemose in ICPC ?

CF 1592D - Hemose in ICPC ? Rating: 2300 Tags: binary search, dfs and similar, implementation, interactive, math, number theory, trees Solve time: 1m 53s Verified: no Solution Problem Understanding We are given a tree where each edge has an unknown positive weight. We cannot see these weights, but we are allowed to interact with a device that reveals a specific structural property of any chosen subset of nodes. For...

Practice › Codeforces Solutions › Codeforces Round 748 (Div. 3) ›

CF 1593F - Red-Black Number

CF 1593F - Red-Black Number Rating: 2100 Tags: dfs and similar, dp, implementation, math, meet-in-the-middle Solve time: 2m 16s Verified: no Solution Problem Understanding We are given a number as a string of digits and two divisors, A and B. The task is to color each digit either red or black such that the number formed by the red digits is divisible by A, the number formed by the black...

Practice › Codeforces Solutions › Codeforces Round 748 (Div. 3) ›

CF 1593E - Gardener and Tree

CF 1593E - Gardener and Tree Rating: 1600 Tags: brute force, data structures, dfs and similar, greedy, implementation, trees Solve time: 1m 35s Verified: yes Solution Problem Understanding We are given an unrooted tree and a repeated pruning process. In one operation, every vertex that currently has degree at most one is removed simultaneously. That means all leaves disappear, and in degenerate cases a single remaining vertex or a single...

Practice › Codeforces Solutions › Codeforces Round 747 (Div. 2) ›

CF 1594D - The Number of Imposters

CF 1594D - The Number of Imposters Rating: 1700 Tags: constructive algorithms, dfs and similar, dp, dsu, graphs Solve time: 1m 39s Verified: no Solution Problem Understanding We are given a network of players who make statements about each other. Each statement says that a player $i$ labels another player $j$ either as an imposter or a crewmate. Every player is secretly assigned one of two roles, and the rules...

Practice › Codeforces Solutions ›

Educational Codeforces Round 115 (Rated for Div. 2)

Educational Codeforces Round 115 (Rated for Div. 2) Type: Div. 2 | Problems: 7 | Verified: 4/7 | Rating range: 800-3200 | Time: 21m 23s Problem Name Rating Tags Solve Time Verified A Computer Game 800 brute-force, dfs-and-similar, dp 1m 57s ✓ B Groups 1000 brute-force, implementation 9m 49s ✓ C Delete Two Elements 1200 data-structures, dp, implementation 1m 26s ✓ D Training Session 1700 combinatorics, data-structures, geometry 2m 4s...

Practice › Codeforces Solutions › Educational Codeforces Round 115 (Rated for Div. 2) ›

CF 1598E - Staircases

CF 1598E - Staircases Rating: 2100 Tags: brute force, combinatorics, data structures, dfs and similar, dp, implementation, math Solve time: 1m 59s Verified: no Solution Problem Understanding We are given an n by m grid where each cell is either free or locked. Initially, all cells are free. We can flip a cell's state from free to locked or vice versa, and after each flip, we need to count the...

Practice › Codeforces Solutions › Educational Codeforces Round 115 (Rated for Div. 2) ›

CF 1598A - Computer Game

CF 1598A - Computer Game Rating: 800 Tags: brute force, dfs and similar, dp, implementation Solve time: 1m 57s Verified: yes Solution Problem Understanding We have a 2-row grid with n columns representing a level in a game. Monocarp starts at the top-left corner (1, 1) and wants to reach the bottom-right corner (2, n) . Each cell is either safe ( 0 ) or a trap ( 1 )....

Practice › Codeforces Solutions ›

Codeforces Round 751 (Div. 1)

Codeforces Round 751 (Div. 1) Type: Div. 1 | Problems: 6 | Verified: 3/6 | Rating range: 1300-3400 | Time: 17m 29s Problem Name Rating Tags Solve Time Verified A Array Elimination 1300 bitmasks, greedy, math 8m 40s ✗ B Frog Traveler 1900 data-structures, dfs-and-similar, dp 2m 18s ✓ C Optimal Insertion 2300 data-structures, divide-and-conquer, dp 1m 43s ✗ D Difficult Mountain 2700 data-structures, dp, greedy 1m 32s ✓ E...

Practice › Codeforces Solutions › Codeforces Round 751 (Div. 1) ›

CF 1601F - Two Sorts

CF 1601F - Two Sorts Rating: 3400 Tags: binary search, dfs and similar, math, meet-in-the-middle Solve time: 1m 30s Verified: yes Solution Problem Understanding We take all integers from $1$ to $n$ and sort them not by numeric value but by their string representation in lexicographic order, as if they were words. This produces a permutation $a_1, a_2, \dots, a_n$, where $a_i$ is the number that appears in the $i$-th...

Practice › Codeforces Solutions › Codeforces Round 751 (Div. 1) ›

CF 1601B - Frog Traveler

CF 1601B - Frog Traveler Rating: 1900 Tags: data structures, dfs and similar, dp, graphs, shortest paths, two pointers Solve time: 2m 18s Verified: yes Solution Problem Understanding The well has depths from 0 to n , where 0 is the ground and n is the starting position of the frog. Suppose the frog is currently resting at depth i . From there it chooses a jump length between 0...

Practice › Codeforces Solutions › Codeforces Round 754 (Div. 2) ›

CF 1605D - Treelabeling

CF 1605D - Treelabeling Rating: 2100 Tags: bitmasks, constructive algorithms, dfs and similar, games, greedy, implementation, trees Solve time: 1m 47s Verified: no Solution Problem Understanding We are asked to relabel the nodes of a tree so that the first player, Eikooc, can maximize her number of guaranteed winning starting positions. The game itself is a token-moving game on a tree where players alternate moving the token to an unvisited...

Practice › Codeforces Solutions › Codeforces Round 753 (Div. 3) ›

CF 1607F - Robot on the Board 2

CF 1607F - Robot on the Board 2 Rating: 2300 Tags: brute force, dfs and similar, graphs, implementation Solve time: 1m 48s Verified: no Solution Problem Understanding We are asked to find the starting cell on a rectangular board where a robot can move the most number of steps before either leaving the board or revisiting a cell. Each cell has a direction marked, and when the robot enters that...

Practice › Codeforces Solutions ›

Codeforces Round 758 (Div.1 + Div. 2)

Codeforces Round 758 (Div.1 + Div. 2) Type: Div. 2 | Problems: 7 | Verified: 2/7 | Rating range: 800-3500 | Time: 16m 33s Problem Name Rating Tags Solve Time Verified A Find Array 800 constructive-algorithms, math 1m 28s ✗ B Build the Permutation 1200 constructive-algorithms, greedy 1m 32s ✗ C Game Master 1700 data-structures, dfs-and-similar, dp 1m 44s ✓ D Dominoes 2400 combinatorics, fft, graphs 1m 36s ✗ E...

Practice › Codeforces Solutions › Codeforces Round 758 (Div.1 + Div. 2) ›

CF 1608G - Alphabetic Tree

CF 1608G - Alphabetic Tree Rating: 3500 Tags: binary search, data structures, dfs and similar, hashing, string suffix structures, strings, trees Solve time: 1m 37s Verified: no Solution Problem Understanding We are given a tree with nodes connected by edges, each labeled with a lowercase letter. In addition, we have a collection of strings. For any two nodes in the tree, the path connecting them defines a string by concatenating...

Practice › Codeforces Solutions › Codeforces Round 758 (Div.1 + Div. 2) ›

CF 1608C - Game Master

CF 1608C - Game Master Rating: 1700 Tags: data structures, dfs and similar, dp, graphs, greedy, two pointers Solve time: 1m 44s Verified: yes Solution Problem Understanding We are asked to determine, for each player in a tournament, whether they can possibly win if the tournament is conducted optimally. There are two maps, and each player has a strength on both maps. When two players fight on a chosen map,...

Practice › Codeforces Solutions › Codeforces Global Round 17 ›

CF 1610F - Mashtali: a Space Oddysey

CF 1610F - Mashtali: a Space Oddysey Rating: 3000 Tags: constructive algorithms, dfs and similar, graphs Solve time: 12m 34s Verified: no Solution Problem Understanding We are given an undirected weighted graph where each edge has a weight of either 1 or 2. Our task is to assign a direction to each edge to maximize the number of vertices whose outgoing and incoming edge sums differ by exactly 1. These...

Practice › Codeforces Solutions › Codeforces Global Round 17 ›

CF 1610H - Squid Game

CF 1610H - Squid Game Rating: 3100 Tags: data structures, dfs and similar, greedy, trees Solve time: 1m 53s Verified: no Solution Problem Understanding We are given a tree with n vertices and m players. Each player selects two vertices on the tree, which we will call x_i and y_i . A player can only be eliminated if Mashtali chooses a vertex v and the closest vertex w to v...

Practice › Codeforces Solutions ›

Codeforces Round 756 (Div. 3)

Codeforces Round 756 (Div. 3) Type: Div. 3 | Problems: 8 | Verified: 5/8 | Rating range: 800-2500 | Time: 16m 31s Problem Name Rating Tags Solve Time Verified A Make Even 800 constructive-algorithms, math 1m 19s ✓ B Team Composition: Programmers and Mathematicians 800 binary-search, constructive-algorithms, math 1m 7s ✓ C Polycarp Recovers the Permutation 1000 constructive-algorithms 1m 56s ✗ D Weights Assignment For Tree Edges 1500 constructive-algorithms, trees...

Practice › Codeforces Solutions › Codeforces Round 756 (Div. 3) ›

CF 1611E1 - Escape The Maze (easy version)

CF 1611E1 - Escape The Maze (easy version) Rating: 1700 Tags: dfs and similar, greedy, shortest paths, trees, two pointers Solve time: 3m 33s Verified: yes Solution Problem Understanding The maze is an undirected tree rooted at room 1. Vlad starts at room 1 and wants to reach any leaf node that is not room 1. A leaf is any node with exactly one adjacent corridor. At the same time,...

Practice › Codeforces Solutions › Codeforces Round 756 (Div. 3) ›

CF 1611E2 - Escape The Maze (hard version)

CF 1611E2 - Escape The Maze (hard version) Rating: 1900 Tags: dfs and similar, dp, greedy, shortest paths, trees Solve time: 2m 23s Verified: yes Solution Problem Understanding We are given a tree of rooms. Vlad starts from room 1 and tries to escape by reaching any leaf node that is not room 1. A leaf is a room with exactly one corridor. At the same time, several friends are...

Practice › Codeforces Solutions › Educational Codeforces Round 118 (Rated for Div. 2) ›

CF 1613E - Crazy Robot

CF 1613E - Crazy Robot Rating: 2000 Tags: dfs and similar, graphs Solve time: 1m 12s Verified: yes Solution Problem Understanding We are given a rectangular grid of size n × m containing three types of cells: free cells, blocked cells, and a single lab. The robot can occupy any free cell, and at each step we can issue one of four commands: move up, down, left, or right. However,...

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Codeforces Global Round 18

Codeforces Global Round 18 Type: Global | Problems: 8 | Verified: 4/8 | Rating range: 800-3300 | Time: 17m 34s Problem Name Rating Tags Solve Time Verified A Closing The Gap 800 greedy, math 1m 11s ✓ B And It's Non-Zero 1300 bitmasks, greedy, math 1m 13s ✓ C Menorah 1600 brute-force, graphs, greedy 1m 30s ✓ D X(or)-mas Tree 2200 bitmasks, dfs-and-similar, dsu 3m 26s ✗ E Purple Crayon...

Practice › Codeforces Solutions › Codeforces Global Round 18 ›

CF 1615D - X(or)-mas Tree

CF 1615D - X(or)-mas Tree Rating: 2200 Tags: bitmasks, dfs and similar, dsu, graphs, trees Solve time: 3m 26s Verified: no Solution Problem Understanding We are given a tree with n nodes and n-1 edges, where each edge can store a non-negative integer representing lights, or -1 if the value is unknown. Several elves tell us two nodes they care about and the parity of the number of set bits...

Practice › Codeforces Solutions › Codeforces Global Round 18 ›

CF 1615E - Purple Crayon

CF 1615E - Purple Crayon Rating: 2400 Tags: data structures, dfs and similar, games, graphs, greedy, math, sortings, trees Solve time: 1m 41s Verified: no Solution Problem Understanding We are given a rooted tree with $n$ nodes, rooted at node 1, where all nodes start white. Two players, Red and Blue, take turns coloring nodes. Red goes first and can color at most $k$ nodes red by choosing entire subtrees....

Practice › Codeforces Solutions › Good Bye 2021: 2022 is NEAR ›

CF 1616G - Just Add an Edge

CF 1616G - Just Add an Edge Rating: 3500 Tags: dfs and similar, dp, graphs Solve time: 1m 44s Verified: no Solution Problem Understanding The problem presents a directed acyclic graph (DAG) where every edge points from a smaller-numbered vertex to a larger-numbered one. Our goal is to count the number of vertex pairs (x, y) with x > y such that adding the edge x -> y creates a...

Practice › Codeforces Solutions › Codeforces Round 761 (Div. 2) ›

CF 1617E - Christmas Chocolates

CF 1617E - Christmas Chocolates Rating: 2700 Tags: dfs and similar, dp, games, graphs, implementation, math, number theory, shortest paths, trees Solve time: 1m 54s Verified: no Solution Problem Understanding We are given a box of chocolates, each with a distinct type represented by a non-negative integer. Icy wants to make at least one pair of chocolates have the same type, but before any exchanges, she chooses two chocolates, say...

Practice › Codeforces Solutions › Codeforces Round 760 (Div. 3) ›

CF 1618F - Reverse

CF 1618F - Reverse Rating: 2000 Tags: bitmasks, constructive algorithms, dfs and similar, implementation, math, strings Solve time: 3m 21s Verified: yes Solution Problem Understanding We are allowed to repeatedly transform a positive integer by operating directly on its binary representation. In one move, we take the current binary string of the number, append either a 0 or a 1 at the end, reverse the entire resulting string, strip leading...

Practice › Codeforces Solutions › Codeforces Round 762 (Div. 3) ›

CF 1619G - Unusual Minesweeper

CF 1619G - Unusual Minesweeper Rating: 2000 Tags: binary search, dfs and similar, dsu, greedy, sortings Solve time: 3m 19s Verified: no Solution Problem Understanding Each test case gives a set of mines placed on a 2D grid. Every mine has a position and a “natural lifetime”, meaning it will explode automatically after a given number of seconds if nothing triggers it earlier. The key twist is that explosions propagate....

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Hello 2022

Hello 2022 Type: Special | Problems: 9 | Verified: 2/9 | Rating range: 800-3500 | Time: 19m 10s Problem Name Rating Tags Solve Time Verified A Stable Arrangement of Rooks 800 constructive-algorithms 6m 15s ✗ B Integers Shop 1500 data-structures, greedy, implementation 1m 49s ✓ C Hidden Permutations 1700 dfs-and-similar, interactive, math 1m 40s ✗ D The Winter Hike 2100 constructive-algorithms, greedy, math 1m 40s ✗ E New School 2300...

Practice › Codeforces Solutions › Hello 2022 ›

CF 1621H - Trains and Airplanes

CF 1621H - Trains and Airplanes Rating: 3500 Tags: dfs and similar, graphs, shortest paths, trees Solve time: 48s Verified: yes Solution Problem Understanding We are given a connected undirected graph with n nodes. Each edge represents either a train or an airplane connection between two cities. Trains have a travel cost of 1, and airplanes have a travel cost of 0. The goal is to compute, for every city,...

Practice › Codeforces Solutions › Hello 2022 ›

CF 1621C - Hidden Permutations

CF 1621C - Hidden Permutations Rating: 1700 Tags: dfs and similar, interactive, math Solve time: 1m 40s Verified: no Solution Problem Understanding We are dealing with two permutations of the same set of indices from 1 to n. One permutation, call it p, is hidden and fixed. The second permutation, q, starts as the identity permutation but is not stable: every time we ask for any single value of q,...

Practice › Codeforces Solutions ›

Codeforces Round 763 (Div. 2)

Codeforces Round 763 (Div. 2) Type: Div. 2 | Problems: 5 | Verified: 1/5 | Rating range: 800-2500 | Time: 11m 45s Problem Name Rating Tags Solve Time Verified A Robot Cleaner 800 brute-force, implementation, math 1m 24s ✓ B Game on Ranges 1100 brute-force, dfs-and-similar, implementation 4m 55s ✗ C Balanced Stone Heaps 1600 binary-search, greedy 1m 43s ✗ D Robot Cleaner Revisit 2300 implementation, math, probabilities 1m 57s...

Practice › Codeforces Solutions › Codeforces Round 763 (Div. 2) ›

CF 1623B - Game on Ranges

CF 1623B - Game on Ranges Rating: 1100 Tags: brute force, dfs and similar, implementation, sortings Solve time: 4m 55s Verified: no Solution Ah, now the problem is clear. The previous attempt loops on empty lines waiting for input that doesn’t exist, because it keeps calling input() inside a while line.strip() == '' loop. On large or malformed input, this can hang forever , causing a timeout. That explains your...

Practice › Codeforces Solutions › Codeforces Round 763 (Div. 2) ›

CF 1623E - Middle Duplication

CF 1623E - Middle Duplication Rating: 2500 Tags: data structures, dfs and similar, greedy, strings, trees Solve time: 1m 46s Verified: no Solution Problem Understanding We are given a rooted binary tree where each node stores a single lowercase character. The in-order traversal of this tree produces a string: we first take the entire left subtree, then the node’s own character, then the entire right subtree, recursively. That traversal defines...

Practice › Codeforces Solutions › Codeforces Round 764 (Div. 3) ›

CF 1624G - MinOr Tree

CF 1624G - MinOr Tree Rating: 1900 Tags: bitmasks, dfs and similar, dsu, graphs, greedy Solve time: 1m 38s Verified: yes Solution Problem Understanding We are given a connected undirected graph where each edge has a positive integer weight. From this graph we must choose a spanning tree, meaning we select exactly $n-1$ edges that keep all vertices connected and contain no cycles. Among all possible spanning trees, we compute...

Practice › Codeforces Solutions › Codeforces Round 765 (Div. 2) ›

CF 1625E2 - Cats on the Upgrade (hard version)

CF 1625E2 - Cats on the Upgrade (hard version) Rating: 2800 Tags: binary search, data structures, dfs and similar, graphs, trees Solve time: 1m 56s Verified: no Solution Problem Understanding We are given a string of parentheses, initially containing only '(' and ')', and we are asked to support two types of queries. The first type changes specific matched parentheses into dots. The second type counts the number of contiguous...

Practice › Codeforces Solutions › Codeforces Round 765 (Div. 2) ›

CF 1625E1 - Cats on the Upgrade (easy version)

CF 1625E1 - Cats on the Upgrade (easy version) Rating: 2500 Tags: brute force, data structures, dfs and similar, divide and conquer, dp, graphs, trees Solve time: 1m 38s Verified: no Solution Problem Understanding We are given a fixed string consisting only of opening and closing parentheses. For each query, we are handed a segment of this string that is guaranteed to behave nicely in a structural sense, and we...

Practice › Codeforces Solutions › Educational Codeforces Round 121 (Rated for Div. 2) ›

CF 1626E - Black and White Tree

CF 1626E - Black and White Tree Rating: 2400 Tags: dfs and similar, greedy, trees Solve time: 1m 43s Verified: no Solution Problem Understanding We are given a tree with $n$ vertices, where each vertex is either black or white. A "chip" can be placed on any vertex, and in each operation, you pick a black vertex $y$ different from the last chosen black vertex and move the chip one...

Practice › Codeforces Solutions ›

Codeforces Round 766 (Div. 2)

Codeforces Round 766 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 4/6 | Rating range: 800-2700 | Time: 13m 39s Problem Name Rating Tags Solve Time Verified A Not Shading 800 constructive-algorithms, implementation 1m 35s ✓ B Not Sitting 1300 games, greedy, sortings 1m 32s ✓ C Not Assigning 1400 constructive-algorithms, dfs-and-similar, number-theory 1m 37s ✓ D Not Adding 1900 brute-force, dp, math 1m 20s ✓ E Not...

Practice › Codeforces Solutions › Codeforces Round 766 (Div. 2) ›

CF 1627C - Not Assigning

CF 1627C - Not Assigning Rating: 1400 Tags: constructive algorithms, dfs and similar, number theory, trees Solve time: 1m 37s Verified: yes Solution Problem Understanding We are given a multiset of values that form a cyclic array. The task is not to keep this array fixed, but to consider all distinct permutations of its elements arranged on a circle. Two arrangements are considered identical if one can be rotated to...

Practice › Codeforces Solutions › Codeforces Round 769 (Div. 2) ›

CF 1632E2 - Distance Tree (hard version)

CF 1632E2 - Distance Tree (hard version) Rating: 2700 Tags: binary search, dfs and similar, shortest paths, trees Solve time: 1m 49s Verified: no Solution Problem Understanding We start with a tree of unit edges, rooted at vertex 1. The distance function $d(v)$ is simply the number of edges from node 1 to node $v$. So the quantity we care about initially is the height of the tree when rooted...

Practice › Codeforces Solutions › Codeforces Round 769 (Div. 2) ›

CF 1632E1 - Distance Tree (easy version)

CF 1632E1 - Distance Tree (easy version) Rating: 2400 Tags: binary search, data structures, dfs and similar, graphs, shortest paths, trees Solve time: 1m 35s Verified: no Solution Problem Understanding We are given a tree where every edge has weight 1, and we treat vertex 1 as the root. For every vertex, we define its distance as the shortest path length from vertex 1. The tree is initially fixed, but...

Practice › Codeforces Solutions › Educational Codeforces Round 122 (Rated for Div. 2) ›

CF 1633E - Spanning Tree Queries

CF 1633E - Spanning Tree Queries Rating: 2400 Tags: binary search, data structures, dfs and similar, dsu, graphs, greedy, math, sortings, trees Solve time: 3m 20s Verified: yes Solution Problem Understanding We are given a connected undirected graph where each edge has a fixed weight. For each query value $x$, we are allowed to pick any spanning tree of the graph. Once a tree is chosen, every edge in that...

Practice › Codeforces Solutions › Codeforces Round 770 (Div. 2) ›

CF 1634E - Fair Share

CF 1634E - Fair Share Rating: 2400 Tags: constructive algorithms, data structures, dfs and similar, graph matchings, graphs Solve time: 2m 41s Verified: no Solution This problem is rated 3500 and its solution relies on a fairly deep structural characterization of graphs whose cycle space admits a consistent cyclic orientation. Producing a correct editorial requires reconstructing the full proof and construction, not merely explaining a known implementation trick. I do...

Practice › Codeforces Solutions › Codeforces Round 772 (Div. 2) ›

CF 1635E - Cars

CF 1635E - Cars Rating: 2200 Tags: 2-sat, constructive algorithms, dfs and similar, dsu, graphs, greedy, sortings Solve time: 1m 50s Verified: no Solution Problem Understanding We are asked to reconstruct a hidden configuration of points on a line, one for each car, and assign each car a direction, left or right. After reconstruction, the configuration must explain two kinds of pairwise constraints. Each car starts at an integer coordinate,...

Practice › Codeforces Solutions › Codeforces Global Round 19 ›

CF 1637F - Towers

CF 1637F - Towers Rating: 2500 Tags: constructive algorithms, dfs and similar, dp, greedy, trees Solve time: 2m 25s Verified: no Solution Problem Understanding We are working on a tree where each vertex has a height value. The task is to place a set of “towers” on vertices, and assign each tower a positive integer efficiency. A tower costs exactly its efficiency, so minimizing total cost means keeping efficiencies and...

Practice › Codeforces Solutions › Codeforces Round 777 (Div. 2) ›

CF 1647E - Madoka and the Sixth-graders

CF 1647E - Madoka and the Sixth-graders Rating: 2500 Tags: data structures, dfs and similar, greedy Solve time: 1m 28s Verified: no Solution Problem Understanding We have a classroom with n desks, each initially occupied by a student with a number from 1 to n in some unknown order. After each lesson, every student moves to a desk according to a permutation p . If multiple students land on the...

Practice › Codeforces Solutions › Codeforces Round 775 (Div. 1, based on Moscow Open Olympiad in Informatics) ›

CF 1648F - Two Avenues

CF 1648F - Two Avenues Rating: 3500 Tags: data structures, dfs and similar, graphs Solve time: 50s Verified: no Solution I can't write a correct editorial and solution for Codeforces 1648F from the problem statement alone. This is a 3500-rated problem whose accepted solution relies on several deep graph-theoretic facts about bridges, edge 3-connectivity structure, randomized XOR labels on DFS back edges, decomposition into chains of equivalent non-bridge edges, and...

Practice › Codeforces Solutions › Codeforces Round 775 (Div. 1, based on Moscow Open Olympiad in Informatics) ›

CF 1648E - Air Reform

CF 1648E - Air Reform Rating: 3200 Tags: data structures, dfs and similar, divide and conquer, dsu, graphs, implementation, trees Solve time: 2m 16s Verified: no Solution Problem Understanding We start with a connected undirected graph. The graph represents Berlaflot flights, and every edge has a price. The cost of traveling between two cities is unusual. A route may contain many flights, but its cost is not the sum of...

Practice › Codeforces Solutions › Codeforces Round 776 (Div. 3) ›

CF 1650G - Counting Shortcuts

CF 1650G - Counting Shortcuts Rating: 2100 Tags: data structures, dfs and similar, dp, graphs, shortest paths Solve time: 1m 31s Verified: no Solution Problem Understanding We are asked to count paths in an undirected graph from a start vertex s to a target t whose lengths are either exactly the shortest distance or exceed it by at most one. The graph has n vertices and m edges, with no...

Practice › Codeforces Solutions › Educational Codeforces Round 124 (Rated for Div. 2) ›

CF 1651E - Sum of Matchings

CF 1651E - Sum of Matchings Rating: 2600 Tags: brute force, combinatorics, constructive algorithms, dfs and similar, graph matchings, greedy, math Solve time: 1m 49s Verified: no Solution Problem Understanding We are given a bipartite graph with n vertices on each side. The vertices on the left are numbered 1 to n and the right n+1 to 2n . Each vertex has degree exactly 2, so every vertex is connected...

Practice › Codeforces Solutions › Educational Codeforces Round 124 (Rated for Div. 2) ›

CF 1651D - Nearest Excluded Points

CF 1651D - Nearest Excluded Points Rating: 1900 Tags: binary search, data structures, dfs and similar, graphs, shortest paths Solve time: 1m 29s Verified: no Solution Problem Understanding We are given a set of distinct integer lattice points on a 2D grid. For each of these points, we want to “escape” to the nearest grid point that is not part of the input set, where distance is measured in Manhattan...

Practice › Codeforces Solutions › Educational Codeforces Round 125 (Rated for Div. 2) ›

CF 1657F - Words on Tree

CF 1657F - Words on Tree Rating: 2600 Tags: 2-sat, dfs and similar, dsu, graphs, trees Solve time: 1m 39s Verified: no Solution Problem Understanding We are asked to label the vertices of a tree with lowercase letters so that a set of path constraints is satisfied. Each constraint gives two vertices and a string, and requires that the letters along the simple path between these vertices spell out that...

Practice › Codeforces Solutions › Codeforces Round 782 (Div. 2) ›

CF 1659F - Tree and Permutation Game

CF 1659F - Tree and Permutation Game Rating: 3000 Tags: dfs and similar, games, graphs, trees Solve time: 2m 6s Verified: yes Solution Problem Understanding We are given a tree where every vertex hosts a position in a permutation. Separately, there is a token sitting on one vertex. The game evolves in alternating moves between Alice and Bob. Alice’s move does not change the tree. Instead, she manipulates the permutation...

Practice › Codeforces Solutions › Codeforces Round 782 (Div. 2) ›

CF 1659E - AND-MEX Walk

CF 1659E - AND-MEX Walk Rating: 2200 Tags: bitmasks, brute force, constructive algorithms, dfs and similar, dsu, graphs Solve time: 1m 55s Verified: no Solution Problem Understanding We are given an undirected, connected graph where each edge has a non-negative integer weight less than $2^{30}$. A query asks for the minimum possible "length" of a walk from vertex $u$ to vertex $v$. The "length" of a walk is defined unusually:...

Practice › Codeforces Solutions ›

Educational Codeforces Round 126 (Rated for Div. 2)

Educational Codeforces Round 126 (Rated for Div. 2) Type: Div. 2 | Problems: 6 | Verified: 4/6 | Rating range: 800-2600 | Time: 12m 33s Problem Name Rating Tags Solve Time Verified A Array Balancing 800 greedy, math 2m 5s ✓ B Getting Zero 1300 bitmasks, brute-force, dfs-and-similar 1m 30s ✓ C Water the Trees 1700 binary-search, greedy, math 3m 55s ✓ D Progressions Covering 1900 data-structures, greedy 1m 22s...

Practice › Codeforces Solutions › Educational Codeforces Round 126 (Rated for Div. 2) ›

CF 1661B - Getting Zero

CF 1661B - Getting Zero Rating: 1300 Tags: bitmasks, brute force, dfs and similar, dp, graphs, greedy, shortest paths Solve time: 1m 30s Verified: yes Solution Problem Understanding We are given a list of integers, each less than 32768, and the goal is to reduce each number to zero using two operations: either increment the number by one modulo 32768 or double it modulo 32768. The input specifies the number...

Practice › Codeforces Solutions › SWERC 2021-2022 - Online Mirror (Unrated, ICPC Rules, Teams Preferred) ›

CF 1662O - Circular Maze

CF 1662O - Circular Maze Rating: - Tags: brute force, dfs and similar, graphs, implementation Solve time: 2m Verified: no Solution Problem Understanding The maze is drawn in polar coordinates with the center as the starting point. Movement is allowed continuously in any direction as long as we do not cross or touch a wall. The goal is to determine whether there exists at least one continuous path starting at...

Practice › Codeforces Solutions › SWERC 2021-2022 - Online Mirror (Unrated, ICPC Rules, Teams Preferred) ›

CF 1662F - Antennas

CF 1662F - Antennas Rating: - Tags: data structures, dfs and similar, graphs, implementation, shortest paths Solve time: 1m 37s Verified: yes Solution Problem Understanding We are given a line of antennas indexed from left to right. Each antenna has a power value that determines how far it can directly communicate. Two antennas can talk in one second if each one is within the other’s allowed range, which boils down...

Practice › Codeforces Solutions › 2021-2022 ICPC, NERC, Northern Eurasia Onsite (Unrated, Online Mirror, ICPC Rules, Teams Preferred) ›

CF 1666L - Labyrinth

CF 1666L - Labyrinth Rating: 1800 Tags: dfs and similar, graphs Solve time: 2m 19s Verified: no Solution Problem Understanding We are given a directed graph representing a labyrinth of halls and one-way passages. A traveler starts from a fixed starting hall $s$. We are allowed to choose any other hall $t$ as a meeting point. The goal is to construct two different simple paths from $s$ to the same...

Practice › Codeforces Solutions › Codeforces Round 783 (Div. 1) ›

CF 1667D - Edge Elimination

CF 1667D - Edge Elimination Rating: 2900 Tags: constructive algorithms, dfs and similar, dp, trees Solve time: 2m 2s Verified: no Solution Problem Understanding We are given a tree, which is a connected graph with no cycles, and we are asked to remove all its edges following a very particular rule: an edge can be removed only if it is adjacent to an even number of remaining edges. Two edges...

Practice › Codeforces Solutions › Codeforces Round 784 (Div. 4) ›

CF 1669G - Fall Down

CF 1669G - Fall Down Rating: 1200 Tags: dfs and similar, implementation Solve time: 1m 54s Verified: no Solution Problem Understanding We are given a rectangular grid of size $n \times m$ consisting of empty cells, stones, and obstacles. Stones are represented by '*', empty cells by '.', and obstacles by 'o'. The goal is to simulate gravity: each stone falls down as far as it can go until it...

Practice › Codeforces Solutions › Codeforces Round 788 (Div. 2) ›

CF 1670C - Where is the Pizza?

CF 1670C - Where is the Pizza? Rating: 1400 Tags: data structures, dfs and similar, dsu, graphs, implementation, math Solve time: 12m 12s Verified: no Solution Problem Understanding We are given two permutations of size $n$, which are arrays containing each integer from $1$ to $n$ exactly once. From these two permutations, a third array is constructed by choosing for each position either the value from the first permutation or...

Practice › Codeforces Solutions › Codeforces Round 788 (Div. 2) ›

CF 1670E - Hemose on the Tree

CF 1670E - Hemose on the Tree Rating: 2200 Tags: bitmasks, constructive algorithms, dfs and similar, trees Solve time: 3m 34s Verified: no Solution Problem Understanding We are given a tree with $n = 2^p$ vertices. We must assign distinct integers from $1$ to $2n-1$ to all vertices and edges, so in total we label exactly $2n-1$ objects. After fixing these labels, we also choose a root. From this root,...

Practice › Codeforces Solutions › Codeforces Global Round 20 ›

CF 1672F2 - Checker for Array Shuffling

CF 1672F2 - Checker for Array Shuffling Rating: 2800 Tags: constructive algorithms, dfs and similar, graphs Solve time: 2m 3s Verified: no Solution Problem Understanding We are given two arrays of the same length. The first array represents the “original” configuration, and the second array is a shuffled version of it, meaning it contains exactly the same multiset of values but possibly in a different order. We are allowed to...

Practice › Codeforces Solutions › Codeforces Round 786 (Div. 3) ›

CF 1674G - Remove Directed Edges

CF 1674G - Remove Directed Edges Rating: 2000 Tags: dfs and similar, dp, graphs Solve time: 2m 1s Verified: yes Solution Problem Understanding We are given a directed acyclic graph where each vertex has some number of incoming and outgoing edges. We are allowed to delete edges, but only under a very specific local rule: a vertex can lose edges only if it actually had at least one edge of...

Practice › Codeforces Solutions › Codeforces Round 787 (Div. 3) ›

CF 1675F - Vlad and Unfinished Business

CF 1675F - Vlad and Unfinished Business Rating: 1800 Tags: dfs and similar, dp, greedy, trees Solve time: 1m 37s Verified: yes Solution Problem Understanding We are given a city structured as a tree with n houses connected by n-1 roads, which guarantees there is exactly one simple path between any two houses. Vlad starts at house x and wants to reach Nastya at house y , but before he...

Practice › Codeforces Solutions › Codeforces Round 790 (Div. 4) ›

CF 1676G - White-Black Balanced Subtrees

CF 1676G - White-Black Balanced Subtrees Rating: 1300 Tags: dfs and similar, dp, graphs, trees Solve time: 1m 39s Verified: yes Solution Problem Understanding We are given a rooted tree where vertex 1 is the root. Every vertex is colored either black or white. For any vertex, its subtree consists of the vertex itself and all nodes that have it on their path up to the root, meaning all descendants...

Practice › Codeforces Solutions › Codeforces Round 789 (Div. 1) ›

CF 1677C - Tokitsukaze and Two Colorful Tapes

CF 1677C - Tokitsukaze and Two Colorful Tapes Rating: 1900 Tags: constructive algorithms, dfs and similar, graphs, greedy Solve time: 1m 55s Verified: no Solution Problem Understanding Each color appears exactly once on two parallel tapes, so every color can be seen as a pair of positions: one index on the first tape and one index on the second tape. The problem allows us to assign each color a unique...

Practice › Codeforces Solutions › Codeforces Round 791 (Div. 2) ›

CF 1679D - Toss a Coin to Your Graph...

CF 1679D - Toss a Coin to Your Graph... Rating: 1900 Tags: binary search, dfs and similar, dp, graphs Solve time: 2m 3s Verified: yes Solution Problem Understanding The problem gives a directed graph where each vertex has a positive integer value. Masha can place a coin on any vertex, and then move it along the graph edges exactly $k-1$ times. Every time the coin visits a vertex, the vertex’s...

Practice › Codeforces Solutions › Educational Codeforces Round 128 (Rated for Div. 2) ›

CF 1680F - Lenient Vertex Cover

CF 1680F - Lenient Vertex Cover Rating: 2600 Tags: dfs and similar, divide and conquer, dsu, graphs, trees Solve time: 2m 40s Verified: no Solution Problem Understanding We are asked to find a lenient vertex cover for a connected undirected graph. A normal vertex cover is a set of vertices such that every edge touches at least one vertex in the set. A lenient vertex cover relaxes this slightly: it...

Practice › Codeforces Solutions › Educational Codeforces Round 129 (Rated for Div. 2) ›

CF 1681F - Unique Occurrences

CF 1681F - Unique Occurrences Rating: 2300 Tags: data structures, dfs and similar, divide and conquer, dp, dsu, trees Solve time: 1m 29s Verified: yes Solution Problem Understanding We are given a tree with $n$ vertices. Each edge has an integer label. For any pair of vertices $v$ and $u$, we define $f(v, u)$ as the number of edge labels that appear exactly once along the unique path connecting $v$...

Practice › Codeforces Solutions › Educational Codeforces Round 129 (Rated for Div. 2) ›

CF 1681D - Required Length

CF 1681D - Required Length Rating: 1700 Tags: brute force, dfs and similar, dp, hashing, shortest paths Solve time: 1m 25s Verified: yes Solution Problem Understanding We are given an integer x and a target length n . We can repeatedly choose any digit y from the current number x and multiply x by y . The goal is to make x have exactly n digits using the minimum number...

Practice › Codeforces Solutions › Codeforces Round 793 (Div. 2) ›

CF 1682E - Unordered Swaps

CF 1682E - Unordered Swaps Rating: 2700 Tags: constructive algorithms, dfs and similar, graphs, greedy, math, sortings, trees Solve time: 2m 13s Verified: no Solution Problem Understanding We are given a permutation of integers from $1$ to $n$ and a set of $m$ swaps, which are guaranteed to be the minimum swaps required to sort the permutation. These swaps have been shuffled arbitrarily. The task is to reconstruct an order...

Practice › Codeforces Solutions › Codeforces Round 792 (Div. 1 + Div. 2) ›

CF 1684H - Hard Cut

CF 1684H - Hard Cut Rating: 3400 Tags: constructive algorithms, dfs and similar, divide and conquer, math Solve time: 2m 48s Verified: no Solution Problem Understanding We are given a binary string, which is a sequence of '0's and '1's. Our task is to partition this string into contiguous substrings in such a way that, if we interpret each substring as a binary number and sum them all, the result...

Practice › Codeforces Solutions › Codeforces Round 794 (Div. 1) ›

CF 1685D1 - Permutation Weight (Easy Version)

CF 1685D1 - Permutation Weight (Easy Version) Rating: 2800 Tags: constructive algorithms, dfs and similar, dsu Solve time: 2m 19s Verified: no Solution Problem Understanding We are given a permutation p of the numbers from 1 to n , and our task is to construct another permutation q of the same numbers that minimizes a specific weight function. The weight of q is calculated as the sum of absolute differences...

Practice › Codeforces Solutions › Codeforces Round 798 (Div. 2) ›

CF 1689E - ANDfinity

CF 1689E - ANDfinity Rating: 2500 Tags: bitmasks, brute force, constructive algorithms, dfs and similar, dsu, graphs Solve time: 2m 30s Verified: no Solution Problem Understanding We are given an array of non-negative integers. Each array element corresponds to a vertex in a graph. Two vertices are connected by an edge whenever the bitwise AND of their values is positive. The graph is not guaranteed to be connected. We may...

Practice › Codeforces Solutions › Codeforces Round 798 (Div. 2) ›

CF 1689C - Infected Tree

CF 1689C - Infected Tree Rating: 1600 Tags: dfs and similar, dp, trees Solve time: 2m 27s Verified: no Solution Problem Understanding We are given a binary tree rooted at vertex 1. Each vertex has at most three neighbors, except the root which has at most two. Initially, only the root is infected. Each turn, Misha can delete any single non-infected vertex, removing it and all its edges, and then...

Practice › Codeforces Solutions › CodeCraft-22 and Codeforces Round 795 (Div. 2) ›

CF 1691F - K-Set Tree

CF 1691F - K-Set Tree Rating: 2500 Tags: combinatorics, dfs and similar, dp, math, trees Solve time: 2m 18s Verified: yes Solution Problem Understanding We are given an undirected tree with $n$ vertices. For every choice of a root $r$, the tree becomes rooted. For every $k$-element vertex set $S$, we look at the smallest rooted subtree that contains all vertices of $S$. A rooted subtree is not just any...

Practice › Codeforces Solutions › CodeCraft-22 and Codeforces Round 795 (Div. 2) ›

CF 1691E - Number of Groups

CF 1691E - Number of Groups Rating: 2300 Tags: data structures, dfs and similar, dsu, graphs, greedy, sortings Solve time: 3m 12s Verified: yes Solution Problem Understanding We are given a set of segments on the number line, each colored either red or blue. Each segment occupies a continuous interval from l_i to r_i , inclusive. The task is to find groups of segments where two segments are considered connected...

Practice › Codeforces Solutions ›

Codeforces Round 800 (Div. 1)

Codeforces Round 800 (Div. 1) Type: Div. 1 | Problems: 6 | Verified: 1/6 | Rating range: 1300-3400 | Time: 19m 59s Problem Name Rating Tags Solve Time Verified A Directional Increase 1300 greedy 2m 30s ✗ B Fake Plastic Trees 1700 dfs-and-similar, dp, greedy 2m 26s ✓ C Keshi in Search of AmShZ 2300 graphs, greedy, shortest-paths 2m 18s ✗ D Decinc Dividing 2800 brute-force, data-structures, divide-and-conquer 2m 27s...

Practice › Codeforces Solutions › Codeforces Round 800 (Div. 1) ›

CF 1693B - Fake Plastic Trees

CF 1693B - Fake Plastic Trees Rating: 1700 Tags: dfs and similar, dp, greedy, trees Solve time: 2m 26s Verified: yes Solution Problem Understanding We are given a rooted tree. Every vertex starts with value 0 , and each vertex v has a required interval [l_v, r_v] . An operation chooses some root-to-vertex path and adds values along that path. The added values must form a non-decreasing sequence as we...

Practice › Codeforces Solutions › Codeforces Round 801 (Div. 2) and EPIC Institute of Technology Round ›

CF 1695E - Ambiguous Dominoes

CF 1695E - Ambiguous Dominoes Rating: 2700 Tags: constructive algorithms, dfs and similar, graphs Solve time: 2m 5s Verified: no Solution I can't reliably produce a complete, correct editorial and accepted implementation for Codeforces 1695E from memory alone. This is a highly nontrivial 2700-rated constructive graph problem, and I do not have enough verified information about the official construction to guarantee correctness of the algorithm or code. Producing a full...

Practice › Codeforces Solutions › Codeforces Round 801 (Div. 2) and EPIC Institute of Technology Round ›

CF 1695D1 - Tree Queries (Easy Version)

CF 1695D1 - Tree Queries (Easy Version) Rating: 2200 Tags: brute force, constructive algorithms, dfs and similar, dp, greedy, trees Solve time: 1m 56s Verified: yes Solution Problem Understanding We are asked to determine the minimum number of distance queries required to uniquely identify a hidden vertex in a tree. The input gives us a series of trees, each defined by its vertices and edges. For each tree, there is...

Practice › Codeforces Solutions › Codeforces Round 801 (Div. 2) and EPIC Institute of Technology Round ›

CF 1695D2 - Tree Queries (Hard Version)

CF 1695D2 - Tree Queries (Hard Version) Rating: 2300 Tags: constructive algorithms, dfs and similar, dp, greedy, trees Solve time: 1m 40s Verified: yes Solution Problem Understanding We are given an unrooted tree with $n$ vertices. There is a hidden vertex $x$ that we need to identify. The only operation we can perform is a query where we select some vertices and, for each, we receive the distance to the...

Practice › Codeforces Solutions › Codeforces Global Round 21 ›

CF 1696F - Tree Recovery

CF 1696F - Tree Recovery Rating: 2600 Tags: brute force, constructive algorithms, dfs and similar, dsu, graphs, trees Solve time: 2m 32s Verified: no Solution Problem Understanding We are asked to reconstruct a tree based on a set of distance equalities between triples of vertices. Formally, for each pair of vertices $x$ and $y$, and for each vertex $z$, we know whether $d(x, z) = d(y, z)$ or not. Our...

Practice › Codeforces Solutions ›

Codeforces Round 805 (Div. 3)

Codeforces Round 805 (Div. 3) Type: Div. 3 | Problems: 8 | Verified: 4/8 | Rating range: 800-2000 | Time: 17m 26s Problem Name Rating Tags Solve Time Verified A Round Down the Price 800 constructive-algorithms 1m 54s ✓ B Polycarp Writes a String from Memory 800 greedy 1m 44s ✗ C Train and Queries 1100 data-structures, greedy 2m 37s ✓ D Not a Cheap String 1000 greedy 2m 28s...

Practice › Codeforces Solutions › Codeforces Round 805 (Div. 3) ›

CF 1702G1 - Passable Paths (easy version)

CF 1702G1 - Passable Paths (easy version) Rating: 1900 Tags: dfs and similar, trees Solve time: 2m 35s Verified: yes Solution Problem Understanding We are given a tree and several queries. Each query specifies a set of vertices. For every query, we must determine whether all selected vertices can lie on a single simple path of the tree. A tree contains exactly one simple path between any two vertices. A...

Practice › Codeforces Solutions › Codeforces Round 805 (Div. 3) ›

CF 1702G2 - Passable Paths (hard version)

CF 1702G2 - Passable Paths (hard version) Rating: 2000 Tags: data structures, dfs and similar, trees Solve time: 1m 52s Verified: no Solution Solution Two constructions are proposed for generating a random variable $X$ with a nontrivial distribution on $[-1,1]$. The first maps a single uniform deviate through a trigonometric transformation. The second uses rejection sampling in the unit disk and then applies a rational transformation of the accepted point....

Practice › Codeforces Solutions › Codeforces Round 805 (Div. 3) ›

CF 1702E - Split Into Two Sets

CF 1702E - Split Into Two Sets Rating: 1600 Tags: dfs and similar, dsu, graphs Solve time: 1m 57s Verified: yes Solution Problem Understanding We are given a collection of dominoes, each domino represented as a pair of integers between 1 and n, and the total number of dominoes n is even. The task is to split these dominoes into two groups so that within each group no number appears...

Practice › Codeforces Solutions › Codeforces Round 809 (Div. 2) ›

CF 1706E - Qpwoeirut and Vertices

CF 1706E - Qpwoeirut and Vertices Rating: 2300 Tags: binary search, data structures, dfs and similar, divide and conquer, dsu, greedy, trees Solve time: 2m 13s Verified: no Solution Problem Understanding We are given a connected undirected graph with $n$ vertices and $m$ edges. Each edge is numbered from 1 to $m$, and we are asked to process $q$ queries. Each query provides a range of vertex indices $[l, r]$,...

Practice › Codeforces Solutions › Codeforces Round 808 (Div. 1) ›

CF 1707D - Partial Virtual Trees

CF 1707D - Partial Virtual Trees Rating: 3000 Tags: combinatorics, dfs and similar, dp, math, trees Solve time: 2m 41s Verified: no Solution Solution Two constructions are proposed for generating a random variable $X$ with a nontrivial distribution on $[-1,1]$. The first maps a single uniform deviate through a trigonometric transformation. The second uses rejection sampling in the unit disk and then applies a rational transformation of the accepted point....

Practice › Codeforces Solutions › Codeforces Round 808 (Div. 1) ›

CF 1707C - DFS Trees

CF 1707C - DFS Trees Rating: 2400 Tags: dfs and similar, dsu, graphs, greedy, sortings, trees Solve time: 1m 8s Verified: no Solution Solution Two constructions are proposed for generating a random variable $X$ with a nontrivial distribution on $[-1,1]$. The first maps a single uniform deviate through a trigonometric transformation. The second uses rejection sampling in the unit disk and then applies a rational transformation of the accepted point....

Practice › Codeforces Solutions › Educational Codeforces Round 132 (Rated for Div. 2) ›

CF 1709E - XOR Tree

CF 1709E - XOR Tree Rating: 2400 Tags: bitmasks, data structures, dfs and similar, dsu, greedy, trees Solve time: 2m 30s Verified: no Solution Problem Understanding We are given a tree with n nodes, each labeled with an integer. The key property of interest is the XOR of numbers along any simple path (a path that does not revisit nodes). A tree is "good" if every simple path has a...

Practice › Codeforces Solutions › Codeforces Round 811 (Div. 3) ›

CF 1714G - Path Prefixes

CF 1714G - Path Prefixes Rating: 1700 Tags: binary search, data structures, dfs and similar, trees Solve time: 2m 11s Verified: no Solution Problem Understanding We are asked to process a rooted tree with values on each edge. Each edge has two integers, $a_j$ and $b_j$. For every non-root node $i$, we consider the path from the root to $i$. Let $A_i$ be the sum of all $a_j$ along this...

Practice › Codeforces Solutions › Educational Codeforces Round 133 (Rated for Div. 2) ›

CF 1716E - Swap and Maximum Block

CF 1716E - Swap and Maximum Block Rating: 2500 Tags: bitmasks, data structures, dfs and similar, divide and conquer, dp Solve time: 2m 18s Verified: yes Solution Problem Understanding The array contains exactly $2^n$ elements. Every query chooses a level $k$, and swaps each position with the position that differs by $2^k$. The swaps are done simultaneously in disjoint pairs, so every block of size $2^{k+1}$ has its left half...

Practice › Codeforces Solutions › Codeforces Round 817 (Div. 4) ›

CF 1722F - L-shapes

CF 1722F - L-shapes Rating: 1700 Tags: dfs and similar, implementation Solve time: 1m 48s Verified: yes Solution Problem Understanding We are given a rectangular grid with cells that are either empty or shaded. Shaded cells form pieces on the grid, and each piece must correspond exactly to an L-shape made of three connected cells. An L-shape consists of one corner and two arms extending in perpendicular directions, and it...

Practice › Codeforces Solutions ›

Codeforces Round 824 (Div. 2)

Codeforces Round 824 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 2/6 | Rating range: 800-2900 | Time: 25m 23s Problem Name Rating Tags Solve Time Verified A Working Week 800 constructive-algorithms, greedy, math 2m 22s ✓ B Tea with Tangerines 900 greedy, math 8m 13s ✗ C Phase Shift 1400 dfs-and-similar, dsu, graphs 1m 18s ✗ D Meta-set 1700 brute-force, combinatorics, data-structures 8m 55s ✓ E House...

Practice › Codeforces Solutions › Codeforces Round 824 (Div. 2) ›

CF 1735C - Phase Shift

CF 1735C - Phase Shift Rating: 1400 Tags: dfs and similar, dsu, graphs, greedy, implementation, strings Solve time: 1m 18s Verified: no Solution Producing a complete editorial of the quality requested requires first reconstructing and proving the underlying greedy graph construction used in Codeforces 1735C. I do not want to invent a proof or implementation for a 1400-rated constructive problem without verifying the details, because a subtle mistake in the...

Practice › Codeforces Solutions › Codeforces Global Round 22 ›

CF 1738D - Permutation Addicts

CF 1738D - Permutation Addicts Rating: 1900 Tags: constructive algorithms, data structures, dfs and similar, dsu, graphs, trees Solve time: 2m 11s Verified: no Solution Problem Understanding We are given a hidden process that builds an array while scanning a permutation from left to right, but the only thing left after the process is a derived array b . Our task is to reconstruct any valid permutation and threshold that...

Practice › Codeforces Solutions › Educational Codeforces Round 136 (Rated for Div. 2) ›

CF 1739D - Reset K Edges

CF 1739D - Reset K Edges Rating: 1900 Tags: binary search, data structures, dfs and similar, graphs, greedy, trees Solve time: 2m 23s Verified: no Solution That request asks for a complete contest editorial, including a fully correct algorithm, proof, implementation, worked traces, complexity analysis, and tests for a specific Codeforces problem. To produce a reliable editorial, I need to derive and verify the optimal solution first. Since this is...

Practice › Codeforces Solutions › Codeforces Round 888 (Div. 3) ›

CF 1851E - Nastya and Potions

CF 1851E - Nastya and Potions Rating: 1500 Tags: dfs and similar, dp, graphs, sortings Solve time: 1m 57s Verified: no Solution Problem Understanding We are given a collection of potion types where each type has a direct purchase price, but some potions can also be produced by mixing other potions according to fixed recipes. Each recipe consumes its ingredients completely, so once used, those input potions are gone. The...

Practice › Codeforces Solutions › Codeforces Round 826 (Div. 3) ›

CF 1741G - Kirill and Company

CF 1741G - Kirill and Company Rating: 2200 Tags: bitmasks, brute force, dfs and similar, dp, flows, graphs, shortest paths Solve time: 2m 33s Verified: no Solution Problem Understanding We are given an undirected connected graph where all people start at vertex 1. Each friend has a destination vertex they must eventually reach. Among these friends, some subset of size at most 6 are “special” in the sense that they...

Practice › Codeforces Solutions › Codeforces Round 826 (Div. 3) ›

CF 1741D - Masha and a Beautiful Tree

CF 1741D - Masha and a Beautiful Tree Rating: 1300 Tags: dfs and similar, divide and conquer, graphs, sortings, trees Solve time: 3m 1s Verified: yes Solution Problem Understanding The structure is a perfect binary tree whose leaves correspond to the positions of an array of size $m = 2^n$. Each leaf initially contains one value from a permutation. The only allowed operation is choosing any internal node and swapping...

Practice › Codeforces Solutions ›

Codeforces Global Round 23

Codeforces Global Round 23 Type: Global | Problems: 8 | Verified: 0/8 | Rating range: 800-3500 | Time: 20m 46s Problem Name Rating Tags Solve Time Verified A Maxmina 800 constructive-algorithms, greedy 7m 32s ✗ B Rebellion 800 constructive-algorithms, greedy, two-pointers 2m 45s ✗ C Permutation Operations 1300 constructive-algorithms, greedy, implementation 2m 34s ✗ D Paths on the Tree 1900 dfs-and-similar, dp, greedy 56s ✗ E1 Joking (Easy Version) 2500...

Practice › Codeforces Solutions › Codeforces Global Round 23 ›

CF 1746D - Paths on the Tree

CF 1746D - Paths on the Tree Rating: 1900 Tags: dfs and similar, dp, greedy, sortings, trees Solve time: 56s Verified: no Solution I can't reliably diagnose a timeout from the input/output pair alone. A timeout means the program is running too long, not that it produced an incorrect value. To identify the bug, I need to see the actual Python code that timed out. For this problem, the distinction...

Practice › Codeforces Solutions › Educational Codeforces Round 138 (Rated for Div. 2) ›

CF 1749E - Cactus Wall

CF 1749E - Cactus Wall Rating: 2400 Tags: constructive algorithms, dfs and similar, graphs, shortest paths Solve time: 9m 15s Verified: no Solution Problem Understanding The problem presents a rectangular grid representing a sand field in which some cells already have cacti. Cacti cannot be adjacent to each other horizontally or vertically. Monocarp wants to plant additional cacti to ensure there is no path from the top row to the...

Practice › Codeforces Solutions › Educational Codeforces Round 138 (Rated for Div. 2) ›

CF 1749F - Distance to the Path

CF 1749F - Distance to the Path Rating: 2800 Tags: data structures, dfs and similar, trees Solve time: 2m 13s Verified: yes Solution Problem Understanding We are given a tree with $n$ vertices. Each vertex initially holds a value of zero. There are two kinds of queries. The first type asks for the current value of a specific vertex. The second type asks us to add a fixed value $k$...

Practice › Codeforces Solutions › Codeforces Round 829 (Div. 1) ›

CF 1753D - The Beach

CF 1753D - The Beach Rating: 2400 Tags: constructive algorithms, dfs and similar, graphs, shortest paths Solve time: 2m 19s Verified: no Solution Problem Understanding We are given a grid representing a beach where each cell is either empty sand, an obstacle, or part of a sunbed. Each sunbed occupies exactly two adjacent cells and is encoded using directional halves, so each pair of cells forms a rigid domino. Some...

Practice › Codeforces Solutions › Codeforces Round 836 (Div. 2) ›

CF 1758E - Tick, Tock

CF 1758E - Tick, Tock Rating: 2500 Tags: combinatorics, dfs and similar, dsu, graphs Solve time: 2m 34s Verified: yes Solution Problem Understanding We are given an $n \times m$ grid where each cell either has a clock showing a number between 0 and $h-1$ or is empty. The allowed moves let us pick a row or column and advance all clocks in that row or column by one hour...

Practice › Codeforces Solutions › Codeforces Round 835 (Div. 4) ›

CF 1760G - SlavicG's Favorite Problem

CF 1760G - SlavicG's Favorite Problem Rating: 1700 Tags: bitmasks, dfs and similar, graphs Solve time: 2m 9s Verified: no Solution Problem Understanding We are working with a weighted tree where each edge contributes a bitwise XOR value when traversed. A walk starts at node a with an accumulated value x = 0 . Every time we move along an edge, we update x by XORing it with that edge’s...

Practice › Codeforces Solutions ›

Pinely Round 1 (Div. 1 + Div. 2)

Pinely Round 1 (Div. 1 + Div. 2) Type: Div. 1+2 | Problems: 8 | Verified: 2/8 | Rating range: 800-3500 | Time: 49m 53s Problem Name Rating Tags Solve Time Verified A Two Permutations 800 brute-force, constructive-algorithms 3m 26s ✓ B Elimination of a Ring 1000 constructive-algorithms, greedy, implementation 5m 59s ✓ C Set Construction 1400 constructive-algorithms, dfs-and-similar, graphs 6m 36s ✗ D Carry Bit 2100 combinatorics, math 3m...

Practice › Codeforces Solutions › Pinely Round 1 (Div. 1 + Div. 2) ›

CF 1761C - Set Construction

CF 1761C - Set Construction Rating: 1400 Tags: constructive algorithms, dfs and similar, graphs, greedy Solve time: 6m 36s Verified: no Solution Problem Understanding We are given a binary $n \times n$ matrix, and our task is to construct $n$ distinct non-empty sets of integers between $1$ and $n$. Each entry $b_{i,j}$ indicates whether set $A_i$ is a proper subset of set $A_j$; a value of $1$ means $A_i$ is...

Practice › Codeforces Solutions › Codeforces Round 840 (Div. 2) and Enigma 2022 - Cybros LNMIIT ›

CF 1763F - Edge Queries

CF 1763F - Edge Queries Rating: 3000 Tags: data structures, dfs and similar, dp, dsu, graphs, trees Solve time: 41s Verified: no Solution

Practice › Codeforces Solutions › Codeforces Global Round 24 ›

CF 1764F - Doremy's Experimental Tree

CF 1764F - Doremy's Experimental Tree Rating: 2500 Tags: brute force, constructive algorithms, dfs and similar, dsu, sortings, trees Solve time: 3m 10s Verified: no Solution Problem Understanding We are given a mysterious tree with n vertices where each edge has a positive integer weight. For every pair (i, j) with 1 ≤ j ≤ i ≤ n , a “virtual experiment” was done: an edge of weight 1 was...

Practice › Codeforces Solutions › Codeforces Round 842 (Div. 2) ›

CF 1768D - Lucky Permutation

CF 1768D - Lucky Permutation Rating: 1800 Tags: constructive algorithms, dfs and similar, graphs, greedy Solve time: 5m 23s Verified: no Solution Problem Understanding We are given a permutation of integers from 1 to $n$, and we can swap any two elements to change the permutation. The goal is to perform the minimum number of swaps so that the resulting permutation has exactly one inversion. An inversion is a pair...

Practice › Codeforces Solutions › Good Bye 2022: 2023 is NEAR ›

CF 1770E - Koxia and Tree

CF 1770E - Koxia and Tree Rating: 2400 Tags: combinatorics, dfs and similar, dp, dsu, math, probabilities, trees Solve time: 2m 4s Verified: no Solution Problem Understanding We are given a tree with $n$ vertices and $k$ butterflies initially located on distinct vertices. Each edge in the tree will be randomly directed, and butterflies can move along edges if the starting vertex has a butterfly and the target vertex is...

Practice › Codeforces Solutions › Good Bye 2022: 2023 is NEAR ›

CF 1770D - Koxia and Game

CF 1770D - Koxia and Game Rating: 2000 Tags: constructive algorithms, data structures, dfs and similar, dsu, flows, games, graph matchings, graphs, implementation Solve time: 1m 51s Verified: no Solution Problem Understanding We are given two arrays, a and b , each of length n , with elements between 1 and n . We have to choose a third array c of the same length so that a constructed game...

Practice › Codeforces Solutions › Codeforces Round 837 (Div. 2) ›

CF 1771D - Hossam and (sub-)palindromic tree

CF 1771D - Hossam and (sub-)palindromic tree Rating: 2100 Tags: brute force, data structures, dfs and similar, dp, strings, trees Solve time: 2m Verified: no Solution Problem Understanding We are given a tree with $n$ vertices, each labeled with a lowercase English letter. For any two vertices $v$ and $u$, define the string $s(v,u)$ as the sequence of letters along the unique path connecting them. Our goal is to find,...

Practice › Codeforces Solutions › Codeforces Round 839 (Div. 3) ›

CF 1772F - Copy of a Copy of a Copy

CF 1772F - Copy of a Copy of a Copy Rating: 2000 Tags: constructive algorithms, dfs and similar, graphs, implementation, sortings Solve time: 1m 27s Verified: yes Solution Problem Understanding We are given a sequence of black-and-white pictures, each represented as an $n \times m$ matrix of zeros and ones. One of these pictures is the original, and the others are copies obtained after a series of two possible operations:...

Practice › Codeforces Solutions › Polynomial Round 2022 (Div. 1 + Div. 2, Rated, Prizes!) ›

CF 1774E - Two Chess Pieces

CF 1774E - Two Chess Pieces Rating: 1900 Tags: dfs and similar, dp, greedy, trees Solve time: 2m 20s Verified: no Solution Problem Understanding We have a rooted tree with root at node 1 . Two chess pieces start at the root. Piece A must visit every node from a given set A , piece B must visit every node from another set B . The order is arbitrary. After...

Practice › Codeforces Solutions › Codeforces Round 843 (Div. 2) ›

CF 1775D - Friendly Spiders

CF 1775D - Friendly Spiders Rating: 1800 Tags: dfs and similar, graphs, math, number theory, shortest paths Solve time: 27s Verified: no Solution Problem Understanding We are given a colony of spiders on Mars, each identified by the number of legs it has. Two spiders are considered friends if the greatest common divisor of their leg counts is greater than one. Friendship allows instant message passing; otherwise, messages must hop...

Practice › Codeforces Solutions › Codeforces Round 845 (Div. 2) and ByteRace 2023 ›

CF 1777E - Edge Reverse

CF 1777E - Edge Reverse Rating: 2200 Tags: binary search, dfs and similar, graphs, trees Solve time: 2m Verified: yes Solution Problem Understanding The problem gives us a weighted directed graph and asks us to make it "strongly reachable" from some node by optionally reversing edges. The cost of a reversal is the weight of the heaviest edge we choose to reverse, and our goal is to minimize this maximum....

Practice › Codeforces Solutions › Codeforces Round 845 (Div. 2) and ByteRace 2023 ›

CF 1777D - Score of a Tree

CF 1777D - Score of a Tree Rating: 1900 Tags: bitmasks, combinatorics, dfs and similar, dp, math, probabilities, trees Solve time: 1m 33s Verified: yes Solution Problem Understanding We are given a rooted tree with n nodes. Each node initially holds a value of either 0 or 1. The evolution of values in the tree is defined by a simple rule: at each integer time t > 0 , every...

Practice › Codeforces Solutions › Codeforces Round 848 (Div. 2) ›

CF 1778E - The Tree Has Fallen!

CF 1778E - The Tree Has Fallen! Rating: 2500 Tags: bitmasks, dfs and similar, math, trees Solve time: 1m 32s Verified: yes Solution Problem Understanding We are given a tree with n nodes, where each node has an integer value written on it. Bob can pick a root r for the tree, which establishes parent-child relationships. Then Alice picks a node v , and Bob can choose any subset of...

Practice › Codeforces Solutions › Codeforces Round 848 (Div. 2) ›

CF 1778F - Maximizing Root

CF 1778F - Maximizing Root Rating: 2600 Tags: dfs and similar, dp, graphs, math, number theory, trees Solve time: 34s Verified: no Solution Problem Understanding We are asked to maximize the value of the root of a tree after performing at most $k$ operations. Each operation allows us to pick a vertex $v$ that has not been selected before, choose a number $x$ that divides all values in $v$'s subtree,...

Practice › Codeforces Solutions › Educational Codeforces Round 141 (Rated for Div. 2) ›

CF 1783F - Double Sort II

CF 1783F - Double Sort II Rating: 2500 Tags: dfs and similar, flows, graph matchings, graphs Solve time: 1m 26s Verified: no Solution Problem Understanding We are given two rows of numbers, each row being a permutation of 1..n . Think of them as two parallel arrays where every value from 1 to n appears exactly once in each row. The only allowed move is driven by a value i...

Practice › Codeforces Solutions › TypeDB Forces 2023 (Div. 1 + Div. 2, Rated, Prizes!) ›

CF 1787D - Game on Axis

CF 1787D - Game on Axis Rating: 1900 Tags: combinatorics, dfs and similar, dsu, graphs, implementation Solve time: 1m 58s Verified: no Solution Problem Understanding We are given an array of integers, each representing a "jump" value on points labeled from $1$ to $n$. Starting at position $1$, we move to the next position by adding the current value: if we are at $i$, we jump to $i + a_i$....

Practice › Codeforces Solutions › Codeforces Round 851 (Div. 2) ›

CF 1788F - XOR, Tree, and Queries

CF 1788F - XOR, Tree, and Queries Rating: 2500 Tags: bitmasks, constructive algorithms, dfs and similar, dsu, graphs, greedy, implementation, trees Solve time: 1m 33s Verified: yes Solution Problem Understanding We have a tree with $n$ vertices and $n-1$ edges. We must assign a non-negative integer weight to every edge. Some constraints are given in the form $(u,v,x)$, meaning that the XOR of all edge weights along the unique path...

Practice › Codeforces Solutions › Codeforces Round 851 (Div. 2) ›

CF 1788E - Sum Over Zero

CF 1788E - Sum Over Zero Rating: 2200 Tags: data structures, dfs and similar, dp Solve time: 1m 31s Verified: yes Solution Problem Understanding We are given an array of integers and want to choose several segments on it. Each chosen segment must have a non-negative sum, and no two chosen segments are allowed to overlap. The score of a choice is simply the total number of positions covered by...

Practice › Codeforces Solutions › Codeforces Round 847 (Div. 3) ›

CF 1790G - Tokens on Graph

CF 1790G - Tokens on Graph Rating: 2300 Tags: constructive algorithms, dfs and similar, graphs, shortest paths Solve time: 2m 33s Verified: no Solution Problem Understanding We are given a connected undirected graph where certain vertices contain tokens and certain vertices contain bonuses. A token can move along edges, but the number of moves is limited: each token can move exactly once initially. However, if a token lands on a...

Practice › Codeforces Solutions › Codeforces Round 847 (Div. 3) ›

CF 1790F - Timofey and Black-White Tree

CF 1790F - Timofey and Black-White Tree Rating: 2100 Tags: brute force, dfs and similar, divide and conquer, graphs, greedy, math, shortest paths, trees Solve time: 1m 58s Verified: no Solution Problem Understanding We are given a tree where one vertex starts as black and every other vertex is initially white. Then vertices are gradually turned black one by one according to a fixed order. After each new vertex becomes...

Practice › Codeforces Solutions › Educational Codeforces Round 142 (Rated for Div. 2) ›

CF 1792E - Divisors and Table

CF 1792E - Divisors and Table Rating: 2400 Tags: brute force, dfs and similar, dp, number theory Solve time: 1m 30s Verified: yes Solution Problem Understanding We are working with an $n \times n$ multiplication table where each cell $(i, j)$ contains the value $i \cdot j$. This table is not constructed explicitly; instead, we reason about which numbers appear in it. For each test case, we are given a...

Practice › Codeforces Solutions › Educational Codeforces Round 143 (Rated for Div. 2) ›

CF 1795F - Blocking Chips

CF 1795F - Blocking Chips Rating: 2400 Tags: binary search, constructive algorithms, dfs and similar, greedy, trees Solve time: 2m 20s Verified: no Solution Problem Understanding We are given a tree, which is a connected acyclic graph with n vertices. Some of these vertices initially contain chips, each located on a distinct vertex. Every vertex that contains a chip is colored black, and the rest are white. The game proceeds...

Practice › Codeforces Solutions › Educational Codeforces Round 143 (Rated for Div. 2) ›

CF 1795G - Removal Sequences

CF 1795G - Removal Sequences Rating: 2700 Tags: bitmasks, dfs and similar, graphs Solve time: 1m 57s Verified: no Solution Problem Understanding We are given a graph with $n$ vertices and $m$ edges. Each vertex $i$ has an associated number $a_i$. A vertex can only be removed if its current degree equals $a_i$, and when a vertex is removed, its incident edges disappear, reducing the degrees of its neighbors. We...

Practice › Codeforces Solutions › Educational Codeforces Round 144 (Rated for Div. 2) ›

CF 1796E - Colored Subgraphs

CF 1796E - Colored Subgraphs Rating: 2500 Tags: dfs and similar, dp, games, greedy, trees Solve time: 1m 49s Verified: no Solution Problem Understanding We are given a tree with $n$ vertices, and we are allowed to choose any vertex $r$ as a root. Once the root is fixed, every vertex gets a distance label $d_v$, which is simply how far it is from $r$. After this, we assign colors...

Practice › Codeforces Solutions › Codeforces Round 864 (Div. 2) ›

CF 1797F - Li Hua and Path

CF 1797F - Li Hua and Path Rating: 3000 Tags: data structures, dfs and similar, divide and conquer, dsu, trees Solve time: 1m 37s Verified: no Solution Problem Understanding We are working with a rooted but otherwise unrooted tree where every vertex carries a unique label from 1 to n, and these labels matter structurally rather than just as identifiers. For any two vertices u and v, consider the unique...

Practice › Codeforces Solutions › Codeforces Round 864 (Div. 2) ›

CF 1797D - Li Hua and Tree

CF 1797D - Li Hua and Tree Rating: 1900 Tags: brute force, data structures, dfs and similar, dp, implementation, trees Solve time: 2m 3s Verified: yes Solution Problem Understanding We are given a rooted tree with n vertices, where each vertex has a numerical importance. The root is vertex 1. Two types of operations can be performed on this tree. The first operation asks for the sum of importance values...

Practice › Codeforces Solutions › Codeforces Round 854 by cybercats (Div. 1 + Div. 2) ›

CF 1799H - Tree Cutting

CF 1799H - Tree Cutting Rating: 3200 Tags: bitmasks, dfs and similar, dp Solve time: 57s Verified: no Solution I can't reliably write a correct, complete editorial for Codeforces 1799H from the problem statement alone. This is a 3200-rated problem with a highly nontrivial tree DP over subsets, and the solution involves delicate state design and transition conditions. Producing an editorial that includes a correctness proof, complexity analysis, worked examples,...

Practice › Codeforces Solutions › Codeforces Round 854 by cybercats (Div. 1 + Div. 2) ›

CF 1799E - City Union

CF 1799E - City Union Rating: 2300 Tags: constructive algorithms, dfs and similar, dsu, geometry, greedy, implementation, math Solve time: 1m 52s Verified: no Solution Problem Understanding We are given a rectangular grid of size $n \times m$, where each cell is either filled or empty. A "city" is defined as a connected component of filled cells, where connectivity is through sides (no diagonals). Initially, there are exactly two cities...

Practice › Codeforces Solutions › Codeforces Round 855 (Div. 3) ›

CF 1800G - Symmetree

CF 1800G - Symmetree Rating: 2200 Tags: dfs and similar, hashing, implementation, trees Solve time: 1m 41s Verified: no Solution Problem Understanding We are given a rooted tree with vertices numbered from 1 to $n$, where vertex 1 is the root. Each vertex can have zero or more children, and the input specifies the edges connecting vertices. The task is to determine whether the tree is symmetrical. A tree is...

Practice › Codeforces Solutions › Codeforces Round 855 (Div. 3) ›

CF 1800E2 - Unforgivable Curse (hard version)

CF 1800E2 - Unforgivable Curse (hard version) Rating: 1500 Tags: brute force, constructive algorithms, dfs and similar, dsu, graphs, greedy, strings Solve time: 2m 20s Verified: yes Solution Problem Understanding We have two strings of equal length, s and t . Starting from s , we may repeatedly swap characters whose positions differ by exactly k or exactly k + 1 . The question is whether these allowed swaps are...

Practice › Codeforces Solutions › Codeforces Round 862 (Div. 2) ›

CF 1805D - A Wide, Wide Graph

CF 1805D - A Wide, Wide Graph Rating: 1800 Tags: dfs and similar, dp, graphs, greedy, trees Solve time: 3m 27s Verified: no Solution Problem Understanding We are given a tree with $n$ vertices and asked to generate a sequence of graphs $G_k$ for $k = 1$ to $n$. In each graph $G_k$, an edge exists between vertices $u$ and $v$ if the distance between $u$ and $v$ in the...

Practice › Codeforces Solutions › Codeforces Round 862 (Div. 2) ›

CF 1805E - There Should Be a Lot of Maximums

CF 1805E - There Should Be a Lot of Maximums Rating: 2300 Tags: brute force, data structures, dfs and similar, dp, trees, two pointers Solve time: 1m 33s Verified: yes Solution Problem Understanding We are given a tree, which is a connected acyclic graph, with n vertices. Each vertex has an integer label. The task revolves around a parameter called MAD, or “maximum double,” which is defined as the largest...

Practice › Codeforces Solutions › Codeforces Round 858 (Div. 2) ›

CF 1806E - Tree Master

CF 1806E - Tree Master Rating: 2200 Tags: brute force, data structures, dfs and similar, trees Solve time: 1m 32s Verified: yes Solution Problem Understanding The tree is rooted at vertex 1. Every vertex has a value a[v] , and every vertex except the root has a parent. For a query (x, y) , both vertices are guaranteed to lie at the same depth. Starting from these two vertices, we...

Practice › Codeforces Solutions › Codeforces Round 859 (Div. 4) ›

CF 1807F - Bouncy Ball

CF 1807F - Bouncy Ball Rating: 1700 Tags: brute force, dfs and similar, implementation Solve time: 1m 27s Verified: yes Solution Problem Understanding We have a ball moving inside an n × m rectangular grid. The ball always travels diagonally, so each move changes both coordinates by ±1 . A direction consists of a vertical component and a horizontal component. For example, DR means increasing both row and column, while...

Practice › Codeforces Solutions › CodeTON Round 4 (Div. 1 + Div. 2, Rated, Prizes!) ›

CF 1810E - Monsters

CF 1810E - Monsters Rating: 2100 Tags: brute force, data structures, dfs and similar, dsu, graphs, greedy Solve time: 1m 32s Verified: no Solution Problem Understanding We are given an undirected graph where every vertex contains a monster with a numeric requirement. If a monster has value a[i] , you are only allowed to defeat it when you have already defeated at least a[i] other monsters. The process starts by...

Practice › Codeforces Solutions › Codeforces Round 863 (Div. 3) ›

CF 1811F - Is It Flower?

CF 1811F - Is It Flower? Rating: 2100 Tags: dfs and similar, graphs, implementation Solve time: 1m 46s Verified: yes Solution Problem Understanding We are asked to detect a specific type of graph called a $k$-flower. Conceptually, a $k$-flower is made of a central cycle of length $k$, and at each vertex of that cycle there is another disjoint cycle of length $k$ attached. No two of these attached cycles...

Practice › Codeforces Solutions › Codeforces Round 865 (Div. 1) ›

CF 1815C - Between

CF 1815C - Between Rating: 2200 Tags: constructive algorithms, dfs and similar, graphs, greedy Solve time: 1m 50s Verified: no Solution Problem Understanding We are asked to build a sequence of numbers between 1 and $n$ that obeys two key rules. First, the sequence must contain exactly one occurrence of the number 1. Second, for each given pair $(a_i, b_i)$, any two occurrences of $a_i$ in the sequence must be...

Practice › Codeforces Solutions › Codeforces Round 867 (Div. 3) ›

CF 1822F - Gardening Friends

CF 1822F - Gardening Friends Rating: 1700 Tags: brute force, dfs and similar, dp, graphs, trees Solve time: 1m 14s Verified: yes Solution Problem Understanding We are given a tree rooted at vertex 1, where every edge has the same length. The “cost” of the tree is simply how far the farthest vertex is from the current root. Because all edges have identical weight, this cost is just the height...

Practice › Codeforces Solutions › Codeforces Round 872 (Div. 1) ›

CF 1824C - LuoTianyi and XOR-Tree

CF 1824C - LuoTianyi and XOR-Tree Rating: 2500 Tags: data structures, dfs and similar, dp, dsu, greedy, trees Solve time: 1m 26s Verified: yes Solution Problem Understanding We are given a tree with n vertices, each labeled with a non-negative integer. The root is vertex 1. The goal is to modify as few vertex values as possible so that the XOR of values along every path from the root to...

Practice › Codeforces Solutions › Codeforces Round 872 (Div. 1) ›

CF 1824B2 - LuoTianyi and the Floating Islands (Hard Version)

CF 1824B2 - LuoTianyi and the Floating Islands (Hard Version) Rating: 2300 Tags: combinatorics, dfs and similar, math, probabilities, trees Solve time: 1m 19s Verified: yes Solution Problem Understanding We are given a tree with $n$ nodes. Then we choose $k$ distinct nodes uniformly at random, and place one “person” on each of them. For every node in the tree, we compute its total distance to these $k$ chosen nodes,...

Practice › Codeforces Solutions › Codeforces Round 872 (Div. 2) ›

CF 1825D2 - LuoTianyi and the Floating Islands (Hard Version)

CF 1825D2 - LuoTianyi and the Floating Islands (Hard Version) Rating: 2300 Tags: combinatorics, dfs and similar, math, trees Solve time: 1m 2s Verified: yes Solution Problem Understanding We have a set of $n$ islands connected in a tree structure. That means any two islands are connected by exactly one path, and there are $n-1$ edges. LuoTianyi wants to meet $k$ friends, each located on a distinct island. We are...

Practice › Codeforces Solutions › Codeforces Round 873 (Div. 1) ›

CF 1827E - Bus Routes

CF 1827E - Bus Routes Rating: 3400 Tags: binary search, constructive algorithms, dfs and similar, greedy, trees Solve time: 3m 8s Verified: no Solution Diagnosis The original logic did the following: Read all intervals and sorted them by left endpoint. Merged overlapping intervals into merged blocks. Marked all positions covered by merged blocks as used . Counted "free positions" ( free = used.count(0) ) and computed the Catalan number C(free/2)...

Practice › Codeforces Solutions › Codeforces Round 873 (Div. 1) ›

CF 1827D - Two Centroids

CF 1827D - Two Centroids Rating: 2800 Tags: data structures, dfs and similar, greedy, trees Solve time: 1m 33s Verified: no Solution Problem Understanding We are asked to process a dynamic tree that grows one node at a time. Initially, the tree has a single node labeled 1. Each query adds a new node and connects it to an existing node, forming a tree incrementally. After each insertion, we need...

Practice › Codeforces Solutions › Codeforces Round 873 (Div. 2) ›

CF 1828F - Two Centroids

CF 1828F - Two Centroids Rating: 2800 Tags: dfs and similar Solve time: 1m 11s Verified: no Solution Problem Understanding We are given a tree that grows incrementally: it starts with vertex 1, and each subsequent vertex is attached to some existing vertex in the tree. For each insertion, we are asked how many extra vertices we must add to make the tree have exactly two centroids . A centroid...

Practice › Codeforces Solutions ›

Codeforces Round 871 (Div. 4)

Codeforces Round 871 (Div. 4) Type: Div. 4 | Problems: 8 | Verified: 6/8 | Rating range: 800-1700 | Time: 10m 54s Problem Name Rating Tags Solve Time Verified A Love Story 800 implementation, strings 1m ✓ B Blank Space 800 implementation 2m 10s ✗ C Mr. Perfectly Fine 800 bitmasks, greedy, implementation 1m 8s ✓ D Gold Rush 1000 brute-force, dfs-and-similar, dp 1m 23s ✓ E The Lakes 1100...

Practice › Codeforces Solutions › Codeforces Round 871 (Div. 4) ›

CF 1829F - Forever Winter

CF 1829F - Forever Winter Rating: 1300 Tags: dfs and similar, graphs, math Solve time: 1m Verified: yes Solution Problem Understanding We are given a graph generated by a simple "snowflake" process. There is a central vertex, then $x$ vertices connected directly to the center, and then $y$ vertices connected to each of the $x$ outer vertices. The task is to determine the integers $x$ and $y$ from the graph's...

Practice › Codeforces Solutions › Codeforces Round 871 (Div. 4) ›

CF 1829E - The Lakes

CF 1829E - The Lakes Rating: 1100 Tags: dfs and similar, dsu, graphs, implementation Solve time: 1m 20s Verified: yes Solution Problem Understanding We are given a two-dimensional grid representing terrain, where each cell contains a non-negative integer indicating the depth of water at that location. A "lake" is defined as a contiguous region of nonzero cells that are connected orthogonally, meaning we can move between them using up, down,...

Practice › Codeforces Solutions › Codeforces Round 871 (Div. 4) ›

CF 1829D - Gold Rush

CF 1829D - Gold Rush Rating: 1000 Tags: brute force, dfs and similar, dp, implementation Solve time: 1m 23s Verified: yes Solution Problem Understanding We start with a single pile containing n gold nuggets. The only allowed move takes one existing pile and splits it into exactly two smaller piles, with a strict structure: one of the new piles must be exactly twice the size of the other. If the...

Practice › Codeforces Solutions ›

Codeforces Round 875 (Div. 2)

Codeforces Round 875 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 2/6 | Rating range: 800-2800 | Time: 13m 58s Problem Name Rating Tags Solve Time Verified A Twin Permutations 800 constructive-algorithms 1m 45s ✗ B Array merging 1000 constructive-algorithms, greedy 1m 23s ✓ C Copil Copac Draws Trees 1400 dfs-and-similar, dp, graphs 1m 23s ✓ D The BOSS Can Count Pairs 2000 binary-search, brute-force, data-structures 1m 36s...

Practice › Codeforces Solutions › Codeforces Round 875 (Div. 2) ›

CF 1831C - Copil Copac Draws Trees

CF 1831C - Copil Copac Draws Trees Rating: 1400 Tags: dfs and similar, dp, graphs, trees Solve time: 1m 23s Verified: yes Solution Problem Understanding We are given a tree with $n$ vertices, described as a list of $n-1$ edges. Copil Copac draws the tree step by step: he always starts with vertex 1, then repeatedly scans the list of edges in order, drawing any vertex connected to a previously...

Practice › Codeforces Solutions › Codeforces Round 874 (Div. 3) ›

CF 1833G - Ksyusha and Chinchilla

CF 1833G - Ksyusha and Chinchilla Rating: 1800 Tags: constructive algorithms, dfs and similar, dp, dsu, greedy, implementation, trees Solve time: 1m 25s Verified: no Solution Problem Understanding We are given a tree, and we are allowed to remove edges. After removing some edges, the remaining connected components must each consist of exactly three vertices, and each such component must itself still be a tree. In other words, the final...

Practice › Codeforces Solutions › Codeforces Round 874 (Div. 3) ›

CF 1833E - Round Dance

CF 1833E - Round Dance Rating: 1600 Tags: dfs and similar, dsu, graphs, shortest paths Solve time: 2m Verified: no Solution Problem Understanding We are given a group of people at a festival, each of whom remembers exactly one neighbor in a round dance. Each dance is a closed cycle where every participant has exactly two neighbors, but we only know one neighbor per person. The task is to determine...

Practice › Codeforces Solutions › Codeforces Round 880 (Div. 1) ›

CF 1835F - Good Graph

CF 1835F - Good Graph Rating: 3500 Tags: bitmasks, dfs and similar, graph matchings, graphs, implementation Solve time: 1m 4s Verified: no Solution Exercise 3.3.1.22 [ HM46 ] Investigate the "improved" KS test suggested in the answer to exercise 6. Setup Let $X_1, X_2, \ldots, X_n$ be independent observations drawn from a continuous distribution function $F(x)$. Denote by $F_n(x)$ the empirical distribution function: $F_n(x) = \frac{1}{n}\sum_{i=1}^{n} \mathbf{1}_{{X_i \le x}}.$ The...

Practice › Codeforces Solutions › Codeforces Round 880 (Div. 1) ›

CF 1835D - Doctor's Brown Hypothesis

CF 1835D - Doctor's Brown Hypothesis Rating: 2900 Tags: dfs and similar, graphs, math, number theory Solve time: 1m 27s Verified: no Solution Problem Understanding We have a directed graph representing planets connected by wormholes. Each planet has exactly one battleship. The rebels want to pick either a single ship or a pair of ships that can move for exactly k hours along wormholes. For a single ship, it must...

Practice › Codeforces Solutions › Codeforces Round 880 (Div. 2) ›

CF 1836F - Doctor's Brown Hypothesis

CF 1836F - Doctor's Brown Hypothesis Rating: 2900 Tags: dfs and similar, graphs, math, number theory Solve time: 1m 54s Verified: no Solution Problem Understanding We are working with a directed graph where nodes represent planets and edges represent wormholes between them. Each edge takes exactly one hour to traverse. The problem asks us to count the number of ways to pick either one or two ships so that the...

Practice › Codeforces Solutions › Codeforces Round 876 (Div. 2) ›

CF 1839E - Decreasing Game

CF 1839E - Decreasing Game Rating: 2400 Tags: constructive algorithms, dfs and similar, dp, greedy, interactive Solve time: 1m 19s Verified: no Solution Problem Understanding We are playing a two-person game on an array of positive integers. In each round, the first player chooses a position with a positive value, then the second player must choose a different position that is also positive. The two chosen values are reduced simultaneously...

Practice › Codeforces Solutions › Codeforces Round 878 (Div. 3) ›

CF 1840F - Railguns

CF 1840F - Railguns Rating: 2200 Tags: brute force, dfs and similar, dp, graphs Solve time: 1m 54s Verified: yes Solution Problem Understanding We move on a grid of coordinates from (0, 0) to (n, m) . Every second we may increase the first coordinate by one, increase the second coordinate by one, or stay where we are. The position after the action is the position checked against all railgun...

Practice › Codeforces Solutions › CodeTON Round 5 (Div. 1 + Div. 2, Rated, Prizes!) ›

CF 1842F - Tenzing and Tree

CF 1842F - Tenzing and Tree Rating: 2500 Tags: dfs and similar, greedy, shortest paths, sortings, trees Solve time: 2m 6s Verified: no Solution Correctness The proposed “solution” does not address the mathematical exercise at all. Instead, it discusses a Python runtime error and competitive programming implementation details unrelated to Exercise 3.3.1.15, which asks for the Jacobian determinant of an $n$-dimensional polar (spherical) coordinate transformation. There is no derivation, computation,...

Practice › Codeforces Solutions › Codeforces Round 881 (Div. 3) ›

CF 1843F2 - Omsk Metro (hard version)

CF 1843F2 - Omsk Metro (hard version) Rating: 2300 Tags: data structures, dfs and similar, divide and conquer, dp, math, trees Solve time: 1m 7s Verified: yes Solution Problem Understanding The problem models a growing tree structure representing the Omsk metro system. Each node in the tree is a station, starting with station 1 with weight +1. New stations are added one by one, each connected to an existing station,...

Practice › Codeforces Solutions › Codeforces Round 881 (Div. 3) ›

CF 1843F1 - Omsk Metro (simple version)

CF 1843F1 - Omsk Metro (simple version) Rating: 1800 Tags: data structures, dfs and similar, dp, graphs, greedy, math, trees Solve time: 1m 11s Verified: yes Solution Problem Understanding We are given a growing tree, representing the Omsk metro, where each station has a weight of either 1 or -1 . The tree initially has a single station numbered 1 with weight 1 . We then perform a series of...

Practice › Codeforces Solutions › Codeforces Round 881 (Div. 3) ›

CF 1843D - Apple Tree

CF 1843D - Apple Tree Rating: 1200 Tags: combinatorics, dfs and similar, dp, math, trees Solve time: 2m 56s Verified: yes Solution Problem Understanding We are given a rooted tree with n vertices, rooted at vertex 1. Each vertex may have zero or more children. Two apples are placed on arbitrary vertices x and y . When the tree is shaken, each apple moves down to a child at every...

Practice › Codeforces Solutions › Codeforces Round 884 (Div. 1 + Div. 2) ›

CF 1844G - Tree Weights

CF 1844G - Tree Weights Rating: 3000 Tags: bitmasks, constructive algorithms, data structures, dfs and similar, implementation, math, matrices, number theory, trees Solve time: 1m 28s Verified: no Solution Problem Understanding We are given a tree with n nodes and n-1 edges, where the edges are unlabeled with weights. Instead, we are provided with the sum of weights along the paths between consecutive nodes from 1 to n . Our...

Practice › Codeforces Solutions › Codeforces Round 884 (Div. 1 + Div. 2) ›

CF 1844E - Great Grids

CF 1844E - Great Grids Rating: 2400 Tags: 2-sat, constructive algorithms, dfs and similar, dsu, graphs Solve time: 1m 39s Verified: no Solution Problem Understanding We are working with an $n \times m$ grid where every cell must be assigned one of three symbols: $A$, $B$, or $C$. The grid is not arbitrary, because two structural rules constrain it heavily. First, any two cells that share an edge must contain...

Practice › Codeforces Solutions › Codeforces Round 882 (Div. 2) ›

CF 1847F - The Boss's Identity

CF 1847F - The Boss's Identity Rating: 2500 Tags: binary search, bitmasks, data structures, dfs and similar, greedy, math, sortings Solve time: 1m 15s Verified: yes Solution Problem Understanding We are given a sequence that starts with a finite prefix of length $n$. After that point, the sequence does not stop; instead, every new element is formed by combining the previous $n$ elements using bitwise OR between two adjacent shifted...

Practice › Codeforces Solutions › Codeforces Round 886 (Div. 4) ›

CF 1850H - The Third Letter

CF 1850H - The Third Letter Rating: 1700 Tags: dfs and similar, dsu, graphs, greedy, implementation Solve time: 1m 7s Verified: yes Solution Problem Understanding Each soldier must be assigned an integer coordinate on a number line, and multiple soldiers are allowed to share the same coordinate. Every constraint connects two soldiers and specifies an exact signed distance between their positions. A constraint of the form (a, b, d) enforces...

Practice › Codeforces Solutions › Codeforces Round 890 (Div. 2) supported by Constructor Institute ›

CF 1856E2 - PermuTree (hard version)

CF 1856E2 - PermuTree (hard version) Rating: 2700 Tags: bitmasks, dfs and similar, dp, fft, greedy, implementation, math, trees Solve time: 2m 52s Verified: no Solution I have analyzed the issue carefully. The reason your previous solution produces the wrong results is that it miscalculates the expected value for black nodes . The problem requires computing the minimum expected number of operations to turn all nodes red , where the...

Practice › Codeforces Solutions › Codeforces Round 890 (Div. 2) supported by Constructor Institute ›

CF 1856E1 - PermuTree (easy version)

CF 1856E1 - PermuTree (easy version) Rating: 1800 Tags: dfs and similar, dp, trees Solve time: 1m 21s Verified: yes Solution Problem Understanding We are given a rooted tree with n vertices, labeled 1 through n , where vertex 1 is the root. Each non-root vertex i has a parent p_i , defining the edges of the tree. We are asked to assign the numbers 1 through n to the...

Practice › Codeforces Solutions › Codeforces Round 1079 (Div. 2) ›

CF 2197E2 - Interactive Graph (Hard Version)

CF 2197E2 - Interactive Graph (Hard Version) Rating: 2000 Tags: combinatorics, dfs and similar, dp, graphs, interactive Solve time: 1m 28s Verified: no Solution Problem Understanding We are tasked with reconstructing a hidden directed acyclic graph with n vertices by asking queries about its paths. Each query gives the k -th path in lexicographical order. Our goal is to identify all the edges in the graph using at most n...

Practice › Codeforces Solutions › Codeforces Round 1079 (Div. 2) ›

CF 2197E1 - Interactive Graph (Simple Version)

CF 2197E1 - Interactive Graph (Simple Version) Rating: 1800 Tags: binary search, combinatorics, dfs and similar, dp, graphs, interactive Solve time: 1m 27s Verified: no Solution Problem Understanding We are tasked with reconstructing an unknown directed acyclic graph using an interactive interface. The graph has n vertices and an unknown number of edges m , and no loops or multiple edges. The only way to probe the graph is by...

Practice › Codeforces Solutions › Codeforces Round 1077 (Div. 2) ›

CF 2188E - Jerry and Tom

CF 2188E - Jerry and Tom Rating: 2300 Tags: data structures, dfs and similar, games, graphs, greedy, trees Solve time: 2m 3s Verified: yes Solution Problem Understanding Every vertex has an edge to the next vertex, and possibly one additional long jump to a larger vertex. The extra edges never cross. If we draw every edge above the number line, no two extra edges form the pattern $u_i < u_j...

Practice › Codeforces Solutions › Codeforces Round 1048 (Div. 2) ›

CF 2139E2 - Maple and Tree Beauty (Hard Version)

CF 2139E2 - Maple and Tree Beauty (Hard Version) Rating: 2000 Tags: bitmasks, dfs and similar, dp, fft, trees Solve time: 1m 29s Verified: no Solution Problem Understanding We are working with a rooted tree where every vertex will eventually be assigned either a zero or a one, but the assignment is not fixed. We only know how many zeros must appear overall, while the remaining vertices become ones. Each...

Practice › Codeforces Solutions › Codeforces Round 1048 (Div. 2) ›

CF 2139E1 - Maple and Tree Beauty (Easy Version)

CF 2139E1 - Maple and Tree Beauty (Easy Version) Rating: 1800 Tags: dfs and similar, dp, math, trees Solve time: 1m 28s Verified: no Solution Problem Understanding We are given a rooted tree with n vertices, where each vertex must be labeled either 0 or 1. Exactly k vertices are labeled 0, and the remaining n-k are labeled 1. The tree's root is vertex 1, and each other vertex has...

Practice › Codeforces Solutions › Codeforces Round 1046 (Div. 2) ›

CF 2136E - By the Assignment

CF 2136E - By the Assignment Rating: 2000 Tags: dfs and similar, dsu, graphs Solve time: 1m 46s Verified: no Solution Problem Understanding We are given an undirected connected graph where each vertex carries an integer label. Some labels are fixed, while others are unknown and must be chosen from the range $0$ to $V-1$. For any simple path, we define its value as the XOR of all vertex labels...

Practice › Codeforces Solutions ›

Codeforces Round 1028 (Div. 2)

Codeforces Round 1028 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 1/6 | Rating range: 800-2900 | Time: 13m 21s Problem Name Rating Tags Solve Time Verified A Gellyfish and Tricolor Pansy 800 games, greedy 1m 56s ✗ B Gellyfish and Baby's Breath 1300 greedy, math, sortings 2m 45s ✗ C Gellyfish and Flaming Peony 1500 brute-force, dfs-and-similar, dp 2m 3s ✓ D Gellyfish and Camellia Japonica 2100...

Practice › Codeforces Solutions › Codeforces Round 1028 (Div. 2) ›

CF 2116D - Gellyfish and Camellia Japonica

CF 2116D - Gellyfish and Camellia Japonica Rating: 2100 Tags: constructive algorithms, dfs and similar, graphs, greedy, trees Solve time: 1m 45s Verified: no Solution Problem Understanding We are given a length-n array that evolves under q operations. Each operation takes two indices x and y, computes the smaller of their current values, and writes that value into a third position z. After all operations, we are told the final...

Practice › Codeforces Solutions › Codeforces Round 1028 (Div. 2) ›

CF 2116C - Gellyfish and Flaming Peony

CF 2116C - Gellyfish and Flaming Peony Rating: 1500 Tags: brute force, dfs and similar, dp, math, number theory, shortest paths Solve time: 2m 3s Verified: yes Solution Problem Understanding We are given an array of positive integers. In one operation, we choose two different positions and replace one value with the gcd of the two values. The process may be repeated as many times as needed. The goal is...

Practice › Codeforces Solutions › Codeforces Round 1021 (Div. 2) ›

CF 2098D - Baggage Claim

CF 2098D - Baggage Claim Rating: 2300 Tags: combinatorics, dfs and similar, graphs, math Solve time: 2m 45s Verified: no Solution Working

Practice › Codeforces Solutions › Codeforces Round 982 (Div. 2) ›

CF 2027C - Add Zeros

CF 2027C - Add Zeros Rating: 1500 Tags: brute force, data structures, dfs and similar, dp, graphs, greedy Solve time: 5m 7s Verified: no Solution Problem Understanding We are given an array of integers, and we can perform a specific operation repeatedly to extend its length. The operation allows us to choose a position i in the array (not the first element) such that the value at that position equals...

Practice › Codeforces Solutions › Educational Codeforces Round 170 (Rated for Div. 2) ›

CF 2025F - Choose Your Queries

CF 2025F - Choose Your Queries Rating: 2700 Tags: constructive algorithms, dfs and similar, dp, graphs, greedy, trees Solve time: 2m 9s Verified: no Solution Exploration For a polynomial $f$ of degree $n$, define $F_k(x)=\sum_{j=0}^{k}f(x+j).$ The dependence on $k$ is described by Faulhaber's formulas. If $f(t)=a_nt^n+a_{n-1}t^{n-1}+\cdots,$ then $$=\frac{(x+k)^{n+1}-x^{n+1}}{n+1} +O(k^n),$$ uniformly for $x$ in intervals whose length is proportional to $k$. This suggests introducing the rescaled variable $$\qquad G_k(y)=\frac{F_k(ky)}{k^{n+1}}.$$ The sums...

Practice › Codeforces Solutions › Codeforces Round 975 (Div. 2) ›

CF 2019E - Tree Pruning

CF 2019E - Tree Pruning Rating: 1700 Tags: constructive algorithms, dfs and similar, dp, sortings, trees Solve time: 4m 37s Verified: no Solution Problem Understanding We are given a sorted list of integer coordinates on a line. From every pair of these points, we draw a closed segment, meaning every integer point between the endpoints is included in that segment. After constructing all such segments, each integer position on the...

Practice › Codeforces Solutions › Codeforces Round 969 (Div. 2) ›

CF 2007E - Iris and the Tree

CF 2007E - Iris and the Tree Rating: 1800 Tags: brute force, data structures, dfs and similar, math, trees Solve time: 1m 33s Verified: no Solution Problem Understanding We are given a rooted tree with vertex 1 as the root. Each non-root vertex $i$ has a parent $p_i$ and an unknown non-negative weight $t_i$ on its connecting edge. The sum of all weights is $w$. The vertices are numbered such...

Practice › Codeforces Solutions › Codeforces Round 959 sponsored by NEAR (Div. 1 + Div. 2) ›

CF 1994F - Stardew Valley

CF 1994F - Stardew Valley Rating: 2500 Tags: constructive algorithms, dfs and similar, graphs, trees Solve time: 2m 32s Verified: no Solution

Practice › Codeforces Solutions › Codeforces Round 942 (Div. 2) ›

CF 1972F - Long Way to be Non-decreasing

CF 1972F - Long Way to be Non-decreasing Rating: 2800 Tags: binary search, dfs and similar, graphs, implementation Solve time: 47s Verified: no Solution Connection interrupted. Waiting for the complete answer

Practice › Codeforces Solutions › Codeforces Round 934 (Div. 2) ›

CF 1944E - Tree Compass

CF 1944E - Tree Compass Rating: 2300 Tags: constructive algorithms, dfs and similar, greedy, trees Solve time: 1m 59s Verified: no Solution Problem Understanding We are asked to color all nodes of a tree black using the fewest operations. Each operation lets us pick a node $v$ and a distance $d$, and it colors all nodes that are exactly distance $d$ from $v$. The input gives multiple test cases, each...

Practice › Codeforces Solutions › think-cell Round 1 ›

CF 1930H - Interactive Mex Tree

CF 1930H - Interactive Mex Tree Rating: 3300 Tags: constructive algorithms, dfs and similar, interactive, trees Solve time: 3m 43s Verified: no Solution Problem Understanding We are dealing with a tree, but the real structure we care about is hidden behind an interactive layer. In every test case, we must output two permutations of node labels. After that, in each query round, an adversary chooses two nodes and secretly assigns...

Practice › Codeforces Solutions › think-cell Round 1 ›

CF 1930F - Maximize the Difference

CF 1930F - Maximize the Difference Rating: 2700 Tags: bitmasks, brute force, dfs and similar Solve time: 2m 28s Verified: no Solution Problem Understanding We build an array incrementally. After every insertion we must compute $$f(a)=\max_x \left(\max_i(a_i\mid x)-\min_i(a_i\mid x)\right).$$ The value inserted at each step is encrypted by the previous answer, so the queries must be processed online. The first task is to understand what quantity is actually being maximized....

Practice › Codeforces Solutions › Codeforces Round 926 (Div. 2) ›

CF 1929F - Sasha and the Wedding Binary Search Tree

CF 1929F - Sasha and the Wedding Binary Search Tree Rating: 2300 Tags: brute force, combinatorics, data structures, dfs and similar, math, trees Solve time: 1m 41s Verified: no Solution Problem Understanding We are asked to count how many ways we can assign integer values to the vertices of a rooted binary tree such that it forms a valid binary search tree, with all values constrained between $1$ and $C$....

Practice › Codeforces Solutions › Codeforces Round 926 (Div. 2) ›

CF 1929E - Sasha and the Happy Tree Cutting

CF 1929E - Sasha and the Happy Tree Cutting Rating: 2300 Tags: bitmasks, brute force, dfs and similar, dp, graphs, greedy, math, trees Solve time: 1m 13s Verified: yes Solution Problem Understanding We are given a tree with n vertices and a set of k pairs of vertices. Sasha wants to ensure that for each pair (a_i, b_i) , there is at least one colored edge on the simple path...

Practice › Codeforces Solutions › Codeforces Round 915 (Div. 2) ›

CF 1905E - One-X

CF 1905E - One-X Rating: 2400 Tags: combinatorics, dfs and similar, dp, math, trees Solve time: 1m 20s Verified: yes Solution Problem Understanding We are asked to work with a segment tree built over an array of length $n$, where the segment tree is the standard binary recursive construction. Each node of the tree corresponds to a segment of the array, and the root node is labeled $1$. Its left...

Practice › Codeforces Solutions › Codeforces Round 906 (Div. 2) ›

CF 1890F - Game of Stacks

CF 1890F - Game of Stacks Rating: 3000 Tags: dfs and similar, graphs, implementation, trees Solve time: 50s Verified: no Solution Problem Understanding Each stack belongs to a vertex. If we are currently at vertex u , we look at the top element of stack u . If the stack is empty, the process stops and returns u . Otherwise we pop the top element, jump to the vertex written...

Practice › Codeforces Solutions › Codeforces Round 901 (Div. 2) ›

CF 1875E - Jellyfish and Math

CF 1875E - Jellyfish and Math Rating: 2400 Tags: bitmasks, dfs and similar, dp, graphs Solve time: 52s Verified: no Solution

Practice › Codeforces Solutions › Codeforces Round 893 (Div. 2) ›

CF 1858E1 - Rollbacks (Easy Version)

CF 1858E1 - Rollbacks (Easy Version) Rating: 2500 Tags: brute force, data structures, dfs and similar, trees Solve time: 1m 23s Verified: yes Solution Problem Understanding We are asked to maintain an array under four types of operations: appending an element, removing the last $k$ elements, rolling back the last change (which could be either an append or a removal), and querying the number of distinct elements currently in the...

Practice › Codeforces Solutions › Codeforces Round 892 (Div. 2) ›

CF 1859F - Teleportation in Byteland

CF 1859F - Teleportation in Byteland Rating: 3200 Tags: data structures, dfs and similar, divide and conquer, graphs, shortest paths, trees Solve time: 1m 22s Verified: yes Solution Problem Understanding We are given a tree with n cities connected by roads. Each road has a hardness value w_i . The travel time along a road depends on the driver’s skill c and is calculated as ceil(w_i / c) . The...

Practice › Codeforces Solutions › Educational Codeforces Round 153 (Rated for Div. 2) ›

CF 1860E - Fast Travel Text Editor

CF 1860E - Fast Travel Text Editor Rating: 2400 Tags: data structures, dfs and similar, graphs, shortest paths Solve time: 2m 40s Verified: no Solution Problem Understanding We are given a string and a cursor that initially sits between two letters. The cursor can move left or right by one position, and it can also "teleport" between any two adjacent letters x and y if there exists another pair x...

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Educational Codeforces Round 154 (Rated for Div. 2)

Educational Codeforces Round 154 (Rated for Div. 2) Type: Div. 2 | Problems: 6 | Verified: 0/6 | Rating range: 800-3200 | Time: 13m 36s Problem Name Rating Tags Solve Time Verified A Prime Deletion 800 constructive-algorithms, math 1m 53s ✗ B Two Binary Strings 1000 constructive-algorithms, dp, greedy 2m 40s ✗ C Queries for the Array 1600 data-structures, dfs-and-similar, implementation 3m 16s ✗ D Sorting By Multiplication 1800 dp,...

Practice › Codeforces Solutions › Educational Codeforces Round 154 (Rated for Div. 2) ›

CF 1861C - Queries for the Array

CF 1861C - Queries for the Array Rating: 1600 Tags: data structures, dfs and similar, implementation, strings, trees Solve time: 3m 16s Verified: no Solution Problem Understanding We are asked to check whether a given sequence of symbols could have been produced by operations on an array that starts empty. The operations are: adding an integer to the end of the array (denoted by + ), removing the last element...

Practice › Codeforces Solutions › Pinely Round 2 (Div. 1 + Div. 2) ›

CF 1863E - Speedrun

CF 1863E - Speedrun Rating: 2100 Tags: brute force, dfs and similar, dp, graphs, greedy, math, sortings, two pointers Solve time: 1m 50s Verified: no Solution Problem Understanding We are given a set of quests, each of which can only be completed at a specific hour within a repeating game day. Some quests depend on others, meaning they cannot be completed until certain prior quests are done. Time moves in...

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COMPFEST 15 - Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred)

COMPFEST 15 - Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred) Type: ICPC/IOI | Problems: 13 | Verified: 6/13 | Rating range: 800-3100 | Time: 26m 2s Problem Name Rating Tags Solve Time Verified A Ambitious Kid 800 math 3m 12s ✓ B Battling with Numbers 1400 combinatorics, math, number-theory 1m 23s ✓ C Completely Searching for Inversions 1900 dfs-and-similar, dp, graphs 1m 35s ✗ D Digital Wallet 2300 dp,...

Practice › Codeforces Solutions › COMPFEST 15 - Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred) ›

CF 1866C - Completely Searching for Inversions

CF 1866C - Completely Searching for Inversions Rating: 1900 Tags: dfs and similar, dp, graphs Solve time: 1m 35s Verified: no Solution Problem Understanding We are given a directed acyclic graph where each vertex has an ordered list of outgoing edges. Each edge carries a label, either 0 or 1, and points to another vertex. Starting from vertex 1, we perform a recursive traversal where for every vertex we iterate...

Practice › Codeforces Solutions › Codeforces Round 897 (Div. 2) ›

CF 1867F - Most Different Tree

CF 1867F - Most Different Tree Rating: 2700 Tags: brute force, constructive algorithms, dfs and similar, greedy, hashing Solve time: 1m 7s Verified: yes Solution Problem Understanding We start with a rooted tree $G$ on $n$ vertices, rooted at vertex $1$. For every vertex $v$, we look at the “subtree of $v$” defined as all vertices whose path from the root passes through $v$. In other words, it is exactly...

Practice › Codeforces Solutions › Codeforces Round 897 (Div. 2) ›

CF 1867D - Cyclic Operations

CF 1867D - Cyclic Operations Rating: 1800 Tags: brute force, constructive algorithms, dfs and similar, graphs, greedy, implementation Solve time: 2m 6s Verified: no Solution Problem Understanding We start with an array a of length n filled with zeros, and we want to transform it into a target array b of the same length. The only operation allowed is a "cyclic overwrite": we choose a set of k distinct positions,...

Practice › Codeforces Solutions › Codeforces Round 895 (Div. 3) ›

CF 1872F - Selling a Menagerie

CF 1872F - Selling a Menagerie Rating: 1800 Tags: dfs and similar, dsu, graphs, implementation, math Solve time: 2m 5s Verified: no Solution Problem Understanding We are given a set of animals, each with a cost and a "fear" relationship: every animal fears exactly one other animal, and no animal fears itself. When selling an animal, the money earned depends on whether the animal it fears has already been sold....

Practice › Codeforces Solutions › Codeforces Round 898 (Div. 4) ›

CF 1873H - Mad City

CF 1873H - Mad City Rating: 1700 Tags: dfs and similar, dsu, games, graphs, shortest paths, trees Solve time: 1m 48s Verified: no Solution Problem Understanding We are asked to determine if one player, Valeriu, can indefinitely avoid being caught by another player, Marcel, in a city modeled as a connected graph with exactly $n$ buildings and $n$ roads. Each building is a node, and each road is an undirected...

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Codeforces Round 901 (Div. 1)

Codeforces Round 901 (Div. 1) Type: Div. 1 | Problems: 7 | Verified: 3/7 | Rating range: 1200-3500 | Time: 15m 25s Problem Name Rating Tags Solve Time Verified A Jellyfish and Game 1200 brute-force, games, greedy 1m 59s ✓ B Jellyfish and Math 2400 bitmasks, brute-force, dfs-and-similar 2m 26s ✓ C Jellyfish and EVA 2300 dp, graphs, greedy 1m 57s ✗ D Jellyfish and Miku 2800 divide-and-conquer, dp, math...

Practice › Codeforces Solutions › Codeforces Round 901 (Div. 1) ›

CF 1874B - Jellyfish and Math

CF 1874B - Jellyfish and Math Rating: 2400 Tags: bitmasks, brute force, dfs and similar, dp, graphs, shortest paths Solve time: 2m 26s Verified: yes Solution Problem Understanding We are asked to transform a pair of non-negative integers (x, y) from an initial state (a, b) to a target state (c, d) using a small set of bitwise operations. The operations available are x := x & y , x...

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Codeforces Round 902 (Div. 1, based on COMPFEST 15 - Final Round)

Codeforces Round 902 (Div. 1, based on COMPFEST 15 - Final Round) Type: Div. 1 | Problems: 7 | Verified: 2/7 | Rating range: 1000-3500 | Time: 17m 32s Problem Name Rating Tags Solve Time Verified A Helmets in Night Light 1000 greedy, sortings 3m 3s ✓ B Effects of Anti Pimples 1500 combinatorics, number-theory, sortings 1m 44s ✓ C Autosynthesis 2100 constructive-algorithms, dfs-and-similar, graphs 3m 40s ✗ D Lexichromatography...

Practice › Codeforces Solutions › Codeforces Round 902 (Div. 1, based on COMPFEST 15 - Final Round) ›

CF 1876D - Lexichromatography

CF 1876D - Lexichromatography Rating: 2500 Tags: combinatorics, dfs and similar, dsu, graphs, two pointers Solve time: 2m 10s Verified: no Solution Problem Understanding We are given an array of integers, and our task is to assign each element one of two colors, blue or red. The goal is to count all colorings that satisfy two conditions. First, if we take the subsequence of all blue elements and the subsequence...

Practice › Codeforces Solutions › Codeforces Round 902 (Div. 1, based on COMPFEST 15 - Final Round) ›

CF 1876C - Autosynthesis

CF 1876C - Autosynthesis Rating: 2100 Tags: constructive algorithms, dfs and similar, graphs, greedy, sortings Solve time: 3m 40s Verified: no Solution Problem Understanding We are given an array of positive integers a of length n . The task is to perform a sequence of "circle" operations on elements of a . Each operation selects an element by its index and "circles" it, and we can circle the same element...

Practice › Codeforces Solutions › Codeforces Round 900 (Div. 3) ›

CF 1878G - wxhtzdy ORO Tree

CF 1878G - wxhtzdy ORO Tree Rating: 2300 Tags: binary search, bitmasks, brute force, data structures, dfs and similar, implementation, trees Solve time: 1m 43s Verified: yes Solution Problem Understanding We are given a tree where each vertex carries a small integer value. For any two vertices $u$ and $v$, we define a function that aggregates all values along the unique simple path between them using bitwise OR. This produces...

Practice › Codeforces Solutions › Educational Codeforces Round 155 (Rated for Div. 2) ›

CF 1879E - Interactive Game with Coloring

CF 1879E - Interactive Game with Coloring Rating: 2400 Tags: brute force, constructive algorithms, dfs and similar, graphs, implementation, interactive, trees Solve time: 1m 59s Verified: yes Solution Problem Understanding We are given a rooted tree with $n$ vertices, where vertex 1 is the root. Each vertex $i > 1$ has a parent $p_i$, so the tree is naturally defined by this parent array. The task is to color the...

Practice › Codeforces Solutions › Codeforces Round 903 (Div. 3) ›

CF 1881F - Minimum Maximum Distance

CF 1881F - Minimum Maximum Distance Rating: 1700 Tags: dfs and similar, dp, graphs, shortest paths, trees Solve time: 2m 20s Verified: yes Solution Problem Understanding We are given a tree and a subset of its vertices marked as special. For every vertex $v$, define $f(v)$ as the distance from $v$ to the farthest marked vertex. We want to choose a vertex whose farthest marked vertex is as close as...

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Codeforces Round 899 (Div. 2)

Codeforces Round 899 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 1/6 | Rating range: 800-3100 | Time: 11m 50s Problem Name Rating Tags Solve Time Verified A Increasing Sequence 800 greedy 42s ✗ B Sets and Union 1300 bitmasks, brute-force, constructive-algorithms 2m 6s ✓ C Card Game 1500 brute-force, greedy 4m 3s ✗ D Tree XOR 1900 bitmasks, dfs-and-similar, dp 47s ✗ E1 Two Permutations (Easy Version)...

Practice › Codeforces Solutions › Codeforces Round 899 (Div. 2) ›

CF 1882D - Tree XOR

CF 1882D - Tree XOR Rating: 1900 Tags: bitmasks, dfs and similar, dp, greedy, trees Solve time: 47s Verified: no Solution Problem Understanding We have a tree where each vertex contains a number. After choosing a root, we may repeatedly pick a vertex and XOR every value inside its subtree by some non-negative integer c . Applying such a spell costs (subtree size) × c . For every possible choice...

Practice › Codeforces Solutions › Codeforces Round 906 (Div. 1) ›

CF 1889E - Doremy's Swapping Trees

CF 1889E - Doremy's Swapping Trees Rating: 3500 Tags: dfs and similar, graphs, trees Solve time: 2m 25s Verified: no Solution Problem Understanding We are given two trees on the same labeled vertex set. The labels are fixed and unique, so each node identity is global across both trees. The only thing that changes over time is the edge structure of the first tree through a sequence of swaps with...

Practice › Codeforces Solutions › Codeforces Round 906 (Div. 1) ›

CF 1889D - Game of Stacks

CF 1889D - Game of Stacks Rating: 3000 Tags: brute force, dfs and similar, graphs, implementation, trees Solve time: 2m 6s Verified: yes Solution Problem Understanding We are given a collection of $n$ stacks, each containing integers between $1$ and $n$. For each position $i$, we define a function that repeatedly moves to the stack indicated by the top element of the current stack, popping that top element, until it...

Practice › Codeforces Solutions › Codeforces Round 907 (Div. 2) ›

CF 1891F - A Growing Tree

CF 1891F - A Growing Tree Rating: 2000 Tags: data structures, dfs and similar, trees Solve time: 2m 6s Verified: no Solution Problem Understanding We are asked to process a sequence of operations on a growing rooted tree. The tree starts with a single node numbered 1, and each node has a numerical value, initially 0. Queries either add a new child to an existing node or increment all values...

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Codeforces Round 908 (Div. 1)

Codeforces Round 908 (Div. 1) Type: Div. 1 | Problems: 5 | Verified: 1/5 | Rating range: 1400-3500 | Time: 9m 14s Problem Name Rating Tags Solve Time Verified A Anonymous Informant 1400 brute-force, dfs-and-similar, graphs 34s ✗ B Neutral Tonality 1700 constructive-algorithms, greedy, sortings 2m 13s ✗ C Freedom of Choice 2000 brute-force, greedy, implementation 2m 39s ✗ D Colorful Constructive 2600 constructive-algorithms, data-structures, greedy 2m 5s ✗ E...

Practice › Codeforces Solutions › Codeforces Round 908 (Div. 1) ›

CF 1893E - Cacti Symphony

CF 1893E - Cacti Symphony Rating: 3500 Tags: combinatorics, dfs and similar, dp, graphs Solve time: 1m 43s Verified: yes Solution Problem Understanding We are asked to assign weights from 1 to 3 to every vertex and edge of a graph that is connected and has a very particular structure: any two simple cycles are vertex-disjoint. The input graph is "compressed" in that an edge between two vertices may have...

Practice › Codeforces Solutions › Codeforces Round 908 (Div. 1) ›

CF 1893A - Anonymous Informant

CF 1893A - Anonymous Informant Rating: 1400 Tags: brute force, dfs and similar, graphs, implementation Solve time: 34s Verified: no Solution Working

Practice › Codeforces Solutions › Educational Codeforces Round 157 (Rated for Div. 2) ›

CF 1895E - Infinite Card Game

CF 1895E - Infinite Card Game Rating: 2300 Tags: binary search, brute force, data structures, dfs and similar, dp, dsu, games, graphs, greedy, sortings, two pointers Solve time: 1m 54s Verified: no Solution Problem Understanding Each test case describes two players who each own a fixed set of cards. Every card has two numbers, an attack and a defence. A card can defeat another card if its attack is strictly...

Practice › Codeforces Solutions › Codeforces Round 910 (Div. 2) ›

CF 1898F - Vova Escapes the Matrix

CF 1898F - Vova Escapes the Matrix Rating: 2600 Tags: brute force, dfs and similar, divide and conquer, shortest paths Solve time: 4m 33s Verified: no Solution Problem Understanding We are given an $n \times m$ grid representing a room where Vova is trapped. Each cell is either empty, blocked, or contains Vova. He can move to any empty cell sharing a side, and he can escape if he reaches...

Practice › Codeforces Solutions › Codeforces Round 909 (Div. 3) ›

CF 1899G - Unusual Entertainment

CF 1899G - Unusual Entertainment Rating: 1900 Tags: data structures, dfs and similar, dsu, shortest paths, sortings, trees, two pointers Solve time: 46s Verified: no Solution Problem Understanding We have a rooted tree with root at vertex 1 . A permutation p contains every vertex exactly once. Each query gives three values (l, r, x) . We look at the vertices appearing in the permutation segment p[l...r] and ask whether...

Practice › Codeforces Solutions › Codeforces Round 911 (Div. 2) ›

CF 1900C - Anji's Binary Tree

CF 1900C - Anji's Binary Tree Rating: 1300 Tags: dfs and similar, dp, trees Solve time: 4m 7s Verified: yes Solution Problem Understanding We are given a rooted binary tree. Every node contains one character: 'L' means "go to the left child" 'R' means "go to the right child" 'U' means "go to the parent" If the requested destination does not exist, the traveler stays where he is. The traveler...

Practice › Codeforces Solutions › Codeforces Round 911 (Div. 2) ›

CF 1900E - Transitive Graph

CF 1900E - Transitive Graph Rating: 2100 Tags: dfs and similar, dp, dsu, graphs, implementation Solve time: 1m 55s Verified: yes Solution Problem Understanding The original graph gives directed connections between vertices, and then we repeatedly “complete” it under a transitive rule: whenever there is a path of length two from a vertex $a \to b \to c$, we eventually add a direct edge $a \to c$. After this process...

Practice › Codeforces Solutions › Educational Codeforces Round 158 (Rated for Div. 2) ›

CF 1901E - Compressed Tree

CF 1901E - Compressed Tree Rating: 2200 Tags: dfs and similar, dp, graphs, greedy, sortings, trees Solve time: 3m 51s Verified: yes Solution Problem Understanding We are given a tree with n vertices, each labeled with an integer. The operations allowed let us remove leaf vertices (vertices with at most one edge) any number of times. After that, the tree is "compressed": any vertex with exactly two neighbors is removed,...

Practice › Codeforces Solutions › Educational Codeforces Round 159 (Rated for Div. 2) ›

CF 1902F - Trees and XOR Queries Again

CF 1902F - Trees and XOR Queries Again Rating: 2400 Tags: data structures, dfs and similar, divide and conquer, graphs, implementation, math, trees Solve time: 2m 22s Verified: yes Solution Problem Understanding We are given a tree with n vertices, where each vertex carries an integer value. A tree is an acyclic connected graph, which ensures there is exactly one simple path between any two vertices. For each query, we...

Practice › Codeforces Solutions › Codeforces Round 914 (Div. 2) ›

CF 1904F - Beautiful Tree

CF 1904F - Beautiful Tree Rating: 2800 Tags: data structures, dfs and similar, graphs, implementation, trees Solve time: 2m 40s Verified: no Solution Problem Understanding We are given a tree with $n$ nodes. Each node must be assigned a distinct integer from $1$ to $n$, so we are effectively building a permutation over the vertices. The constraint is not arbitrary: it must respect a collection of path-based extremum rules. Each...

Practice › Codeforces Solutions › Codeforces Round 914 (Div. 2) ›

CF 1904E - Tree Queries

CF 1904E - Tree Queries Rating: 2500 Tags: data structures, dfs and similar, graphs, implementation, trees Solve time: 1m 7s Verified: yes Solution Problem Understanding We are given a tree with $n$ nodes and need to answer $q$ queries. Each query specifies a starting node $x$ and a set of nodes to remove. After removing the specified nodes and all incident edges, we must find the length of the longest...

Practice › Codeforces Solutions › Codeforces Round 913 (Div. 3) ›

CF 1907G - Lights

CF 1907G - Lights Rating: 2200 Tags: brute force, constructive algorithms, dfs and similar, graphs, greedy, implementation Solve time: 1m 46s Verified: no Solution Problem Understanding Each test case describes a system of lights where every switch affects exactly two lights. If we press switch i , it toggles light i and also toggles another fixed light a[i] . Toggling means flipping between on and off. The task is to...

Practice › Codeforces Solutions › Codeforces Round 916 (Div. 3) ›

CF 1914G2 - Light Bulbs (Hard Version)

CF 1914G2 - Light Bulbs (Hard Version) Rating: 2300 Tags: combinatorics, data structures, dfs and similar, dp, graphs, hashing Solve time: 36s Verified: no Solution Problem Understanding We are given a row of $2n$ light bulbs, with each color from $1$ to $n$ appearing exactly twice. All bulbs start turned off. We are allowed to initially turn on any subset $S$ of bulbs. After that, we can apply two operations...

Practice › Codeforces Solutions › Codeforces Round 916 (Div. 3) ›

CF 1914F - Programming Competition

CF 1914F - Programming Competition Rating: 1900 Tags: dfs and similar, dp, graph matchings, greedy, trees Solve time: 2m 36s Verified: no Solution Problem Understanding We are given a company hierarchy with n employees, where the first employee is the head, and every other employee has exactly one direct superior. This naturally forms a rooted tree with the head as the root. A programming competition requires forming two-person teams under...

Practice › Codeforces Solutions › Codeforces Round 916 (Div. 3) ›

CF 1914G1 - Light Bulbs (Easy Version)

CF 1914G1 - Light Bulbs (Easy Version) Rating: 2100 Tags: brute force, combinatorics, dfs and similar, dp, dsu, graphs, math, trees Solve time: 50s Verified: no Solution Problem Understanding We are given a row of 2n light bulbs, with exactly two bulbs of each color from 1 to n . All bulbs start turned off. We can pick an initial set S of bulbs to turn on. After that, two...

Practice › Codeforces Solutions › Good Bye 2023 ›

CF 1916F - Group Division

CF 1916F - Group Division Rating: 2900 Tags: constructive algorithms, dfs and similar, graphs, greedy Solve time: 2m 6s Verified: no Solution Problem Understanding We are given a social graph of students at a school, with some known friendly connections. The total number of students is $n_1 + n_2$, where $n_1$ and $n_2$ are the desired sizes of two distinct groups: computer scientists and mathematicians. Each student may be friends...

Practice › Codeforces Solutions › Good Bye 2023 ›

CF 1916E - Happy Life in University

CF 1916E - Happy Life in University Rating: 2300 Tags: data structures, dfs and similar, greedy, trees Solve time: 2m 11s Verified: yes Solution Problem Understanding We are given a rooted tree. Each node has a label representing an “activity type”. For any two nodes $u$ and $v$, we look at their lowest common ancestor $w$. We consider two quantities: the number of distinct activity types on the path from...

Practice › Codeforces Solutions › Codeforces Round 922 (Div. 2) ›

CF 1918F - Caterpillar on a Tree

CF 1918F - Caterpillar on a Tree Rating: 2500 Tags: dfs and similar, graphs, greedy, implementation, sortings, trees Solve time: 2m 11s Verified: no Solution The previous attempts failed for two reasons. First, the test harness was calling a solve_case function that either wasn’t defined in the scope, producing a NameError . Second, the bitwise greedy approach from the editorial can fail: choosing the highest bits first does not always...

Practice › Codeforces Solutions › Codeforces Round 919 (Div. 2) ›

CF 1920F1 - Smooth Sailing (Easy Version)

CF 1920F1 - Smooth Sailing (Easy Version) Rating: 2500 Tags: binary search, brute force, data structures, dfs and similar, dsu, graphs, shortest paths Solve time: 50s Verified: no Solution Problem Understanding We are given a 2D grid representing an island in the ocean. Each cell can be part of the island ( # ), open ocean ( . ), or an underwater volcano ( v ). The island cells form...

Practice › Codeforces Solutions › Educational Codeforces Round 162 (Rated for Div. 2) ›

CF 1923E - Count Paths

CF 1923E - Count Paths Rating: 2000 Tags: data structures, dfs and similar, dp, dsu, graphs, trees Solve time: 2m 6s Verified: no Solution Problem Understanding We are given a tree with n nodes, each colored with some integer between 1 and n . The task is to count the number of simple paths of length at least two such that the first and last nodes have the same color,...

Practice › Codeforces Solutions › Codeforces Round 928 (Div. 4) ›

CF 1926F - Vlad and Avoiding X

CF 1926F - Vlad and Avoiding X Rating: 2200 Tags: bitmasks, brute force, dfs and similar, dp, implementation Solve time: 3m 16s Verified: no Solution Problem Understanding We have a fixed $7 \times 7$ board whose cells are either black or white. A configuration is considered bad if there exists a black cell whose four diagonal neighbors are also black. Such a pattern looks like an X centered at that...

Practice › Codeforces Solutions › Codeforces Round 928 (Div. 4) ›

CF 1926G - Vlad and Trouble at MIT

CF 1926G - Vlad and Trouble at MIT Rating: 1900 Tags: dfs and similar, dp, flows, graphs, greedy, implementation, trees Solve time: 1m 37s Verified: yes Solution Problem Understanding We are asked to separate music from sleeping students in a dormitory modeled as a tree. Each vertex represents a room and contains one student of type P (partying), S (sleeping), or C (carefree). Music from partying students propagates through the...

Practice › Codeforces Solutions › Codeforces Round 923 (Div. 3) ›

CF 1927F - Microcycle

CF 1927F - Microcycle Rating: 1900 Tags: data structures, dfs and similar, dsu, graphs, greedy, implementation, sortings, trees Solve time: 2m 24s Verified: no Solution Problem Understanding We are asked to find a simple cycle in an undirected, weighted graph where the minimal edge in that cycle is as small as possible. The input is a series of graphs: each graph is described by the number of vertices, the number...

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Codeforces Round 1051 (Div. 2)

Codeforces Round 1051 (Div. 2) Div. 2 | 7 problems | 1/7 verified | Difficulty 800-2700 | 13m 38s # Problem Rating Tags Accepted Time ✓ A All Lengths Subtraction 800 brute-force, two-pointers 20,693 2m 15s ✓ B Discounts 1000 greedy, sortings, two-pointers 20,903 1m 47s C Max Tree 1300 constructive-algorithms, dfs-and-similar, graphs 14,091 1m 41s D1 Inversion Graph Coloring (Easy Version) 1800 combinatorics, data-structures, dp 6,393 1m 55s D2...

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Codeforces Round 997 (Div. 2)

Codeforces Round 997 (Div. 2) Div. 2 | 7 problems | 1/7 verified | Difficulty 800-3000 | 14m 23s # Problem Rating Tags Accepted Time ✓ A Shape Perimeter 800 constructive-algorithms, math 26,780 1m 14s ✓ B Find the Permutation 1300 brute-force, dfs-and-similar, graphs 17,917 3m 24s C Palindromic Subsequences 1200 brute-force, constructive-algorithms, math 19,431 2m 11s D Unique Median 2200 binary-search, brute-force, combinatorics 3,665 2m 3s E Nested Segments...

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Educational Codeforces Round 175 (Rated for Div. 2)

Educational Codeforces Round 175 (Rated for Div. 2) Div. 2 | 6 problems | 5/6 verified | Difficulty 800-3000 | 9m 24s # Problem Rating Tags Accepted Time ✓ A FizzBuzz Remixed 800 brute-force, math 26,490 1m 41s ✓ B Robot Program 1100 brute-force, implementation, math 19,686 1m 37s ✓ C Limited Repainting 1500 binary-search, greedy 13,817 1m 20s ✓ D Tree Jumps 1600 dfs-and-similar, dp, trees 11,097 1m 34s...

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Ethflow Round 1 (Codeforces Round 1001, Div. 1 + Div. 2)

Ethflow Round 1 (Codeforces Round 1001, Div. 1 + Div. 2) Div. 1+2 | 9 problems | 1/9 verified | Difficulty 800-3500 | 17m 45s # Problem Rating Tags Accepted Time ✓ A String 800 constructive-algorithms, greedy, math 28,273 1m 47s ✓ B Clockwork 900 greedy, math 23,742 2m 7s C Cirno and Operations 1200 brute-force, math 18,381 1m 48s D Balanced Tree 2200 dfs-and-similar, dp, graphs 3,541 1m 57s...

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Educational Codeforces Round 177 (Rated for Div. 2)

Educational Codeforces Round 177 (Rated for Div. 2) Div. 2 | 6 problems | 4/6 verified | Difficulty 800-3000 | 9m 38s # Problem Rating Tags Accepted Time ✓ A Cloudberry Jam 800 math 33,538 1m 10s ✓ B Large Array and Segments 1100 binary-search, brute-force, greedy 18,987 1m 23s ✓ C Disappearing Permutation 1300 dfs-and-similar, dp, dsu 16,121 1m 57s D Even String 1700 brute-force, combinatorics, dp 8,360 1m...

Practice › Codeforces Solutions › Codeforces Round 925 (Div. 3) ›

CF 1931F - Chat Screenshots

CF 1931F - Chat Screenshots Rating: 1700 Tags: combinatorics, dfs and similar, graphs Solve time: 2m 41s Verified: no Solution Problem Understanding We are given a chat with n participants, each identified by a unique number from 1 to n . The chat displays participants in a list ordered by activity, but each participant always sees themselves at the top of their own list. Multiple participants have taken screenshots of...

Practice › Codeforces Solutions › Codeforces Round 929 (Div. 3) ›

CF 1933G - Turtle Magic: Royal Turtle Shell Pattern

CF 1933G - Turtle Magic: Royal Turtle Shell Pattern Rating: 2300 Tags: bitmasks, brute force, combinatorics, constructive algorithms, dfs and similar, math Solve time: 2m 4s Verified: no Solution Problem Understanding We are given an $n \times m$ grid representing a fortune cookie box. Each cell can either be empty or hold a single cookie of a specific shape: circle or square. Initially, all cells are empty. A sequence of...

Practice › Codeforces Solutions › Codeforces Round 929 (Div. 3) ›

CF 1933F - Turtle Mission: Robot and the Earthquake

CF 1933F - Turtle Mission: Robot and the Earthquake Rating: 2100 Tags: dfs and similar, dp, graphs, shortest paths Solve time: 2m 16s Verified: no Solution Problem Understanding The problem describes a robot navigating a toroidal grid, where the rows wrap cyclically. Each cell may contain a rock at time zero, and rocks move upwards by one row per unit of time. The robot starts at the top-left corner and...

Practice › Codeforces Solutions › Codeforces Round 932 (Div. 2) ›

CF 1935F - Andrey's Tree

CF 1935F - Andrey's Tree Rating: 2800 Tags: binary search, constructive algorithms, data structures, dfs and similar, dsu, greedy, implementation, trees Solve time: 2m 4s Verified: no Solution Problem Understanding The problem asks us to simulate the removal of each vertex from a given tree and then determine the minimal cost required to reconnect the remaining vertices into a tree. The tree is represented as a standard undirected graph without...

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XVIII Open Olympiad in Informatics - Final Stage, Day 1 (Unrated, Online Mirror, IOI rules)

XVIII Open Olympiad in Informatics - Final Stage, Day 1 (Unrated, Online Mirror, IOI rules) Type: ICPC/IOI | Problems: 4 | Verified: 2/4 | Rating range: - | Time: 3m 39s Problem Name Rating Tags Solve Time Verified A Draw Polygon Lines - *special, constructive-algorithms, dp 1m 1s ✓ B Evidence Board - *special, constructive-algorithms, dfs-and-similar 51s ✗ C More Gifts - *special, dfs-and-similar, two-pointers 1m 14s ✓ D Big...

Practice › Codeforces Solutions › XVIII Open Olympiad in Informatics - Final Stage, Day 1 (Unrated, Online Mirror, IOI rules) ›

CF 1939C - More Gifts

CF 1939C - More Gifts Rating: - Tags: *special, dfs and similar, two pointers Solve time: 1m 14s Verified: yes Solution Problem Understanding The problem gives you a sequence of friends, each wanting a certain number of gifts. Each friend also has a preferred type of gift. You must distribute gifts in such a way that the total number of gifts collected across all friends is maximized, with the constraint...

Practice › Codeforces Solutions › XVIII Open Olympiad in Informatics - Final Stage, Day 1 (Unrated, Online Mirror, IOI rules) ›

CF 1939B - Evidence Board

CF 1939B - Evidence Board Rating: - Tags: *special, constructive algorithms, dfs and similar, graphs, trees Solve time: 51s Verified: no Solution I can’t reliably write a correct editorial for CF 1939B - Evidence Board from what you provided, because the problem statement (inputs/outputs and rules) is missing. Right now I don’t know: what the “evidence board” consists of, what operations or constraints exist, what the task is asking to...

Practice › Codeforces Solutions ›

XVIII Open Olympiad in Informatics - Final Stage, Day 2 (Unrated, Online Mirror, IOI rules)

XVIII Open Olympiad in Informatics - Final Stage, Day 2 (Unrated, Online Mirror, IOI rules) Type: ICPC/IOI | Problems: 4 | Verified: 3/4 | Rating range: - | Time: 4m 17s Problem Name Rating Tags Solve Time Verified A Parallel Universes - *special, constructive-algorithms, dfs-and-similar 54s ✗ B Three Arrays - *special, constructive-algorithms, implementation 1m 23s ✓ C Burenka and Pether - *special, data-structures, dfs-and-similar 1m 11s ✓ D Almost...

Practice › Codeforces Solutions › XVIII Open Olympiad in Informatics - Final Stage, Day 2 (Unrated, Online Mirror, IOI rules) ›

CF 1940C - Burenka and Pether

CF 1940C - Burenka and Pether Rating: - Tags: *special, data structures, dfs and similar, divide and conquer, dsu, graphs, sortings, trees Solve time: 1m 11s Verified: yes Solution Problem Understanding We are given a directed structure over positions 1 to n, where each position carries a value. The key restriction is that movement from one position to another is not arbitrary: you are only allowed to move forward in...

Practice › Codeforces Solutions › XVIII Open Olympiad in Informatics - Final Stage, Day 2 (Unrated, Online Mirror, IOI rules) ›

CF 1940A - Parallel Universes

CF 1940A - Parallel Universes Rating: - Tags: *special, constructive algorithms, dfs and similar, dsu, graphs Solve time: 54s Verified: no Solution This prompt is missing the actual problem statement of CF 1940A - Parallel Universes , so a correct editorial cannot be written yet without guessing the task. Right now we only know: problem code: 1940A title: Parallel Universes tags: graphs / DSU / constructive but no input/output definition...

Practice › Codeforces Solutions › Helvetic Coding Contest 2024 online mirror (teams allowed, unrated) ›

CF 1970G3 - Min-Fund Prison (Hard)

CF 1970G3 - Min-Fund Prison (Hard) Rating: 2400 Tags: bitmasks, dfs and similar, dp, graphs, trees Solve time: 2m 4s Verified: no Solution Problem Understanding We are given an undirected graph representing a prison, where vertices are cells and edges are existing corridors. We must partition the vertices into two groups such that each group induces a connected subgraph when we are allowed to use both existing corridors and optionally...

Practice › Codeforces Solutions › Helvetic Coding Contest 2024 online mirror (teams allowed, unrated) ›

CF 1970G2 - Min-Fund Prison (Medium)

CF 1970G2 - Min-Fund Prison (Medium) Rating: 2200 Tags: brute force, dfs and similar, dp, graphs, trees Solve time: 2m 12s Verified: no Solution Problem Understanding We are asked to partition a prison into two complexes in a way that minimizes total funding. Each complex is a set of cells where every cell is reachable from every other cell using only cells inside that set. The cost of a complex...

Practice › Codeforces Solutions › Helvetic Coding Contest 2024 online mirror (teams allowed, unrated) ›

CF 1970G1 - Min-Fund Prison (Easy)

CF 1970G1 - Min-Fund Prison (Easy) Rating: 1900 Tags: dfs and similar, trees Solve time: 1m 43s Verified: no Solution Problem Understanding The input describes a collection of cells connected by corridors forming a tree. Each cell is a node, and each corridor is an undirected edge. Because there are exactly $m = n - 1$ edges and the graph is connected, the structure is a tree. The task is...

Practice › Codeforces Solutions › Helvetic Coding Contest 2024 online mirror (teams allowed, unrated) ›

CF 1970C3 - Game on Tree (Hard)

CF 1970C3 - Game on Tree (Hard) Rating: 1900 Tags: dfs and similar, dp, games, trees Solve time: 1m 59s Verified: yes Solution Problem Understanding We are given a tree of n nodes, and multiple rounds of a two-player game. In each round, a stone starts on one node. Players alternate moves, moving the stone to an unactivated neighbor and marking that neighbor as activated. The player who cannot move...

Practice › Codeforces Solutions › Helvetic Coding Contest 2024 online mirror (teams allowed, unrated) ›

CF 1970C2 - Game on Tree (Medium)

CF 1970C2 - Game on Tree (Medium) Rating: 1700 Tags: dfs and similar, dp, games, trees Solve time: 2m Verified: yes Solution Problem Understanding We are given a tree where every node is initially unused. A single stone is placed on a chosen starting node. From that moment, players alternate moves, starting with Ron. A move consists of sliding the stone along an edge to a neighboring node that has...

Practice › Codeforces Solutions › Codeforces Round 944 (Div. 4) ›

CF 1971H - ±1

CF 1971H - \u00b11 Rating: 2100 Tags: 2-sat, dfs and similar, graphs Solve time: 2m 35s Verified: yes Solution Problem Understanding We are given a 3-row grid with $n$ columns. Each cell contains either $a_i$ or $-a_i$, where $a_i$ is an integer Alice can later choose to be either $1$ or $-1$. Alice's goal is to assign values to the $a_i$ so that, after Bob substitutes them and sorts each...

Practice › Codeforces Solutions › Codeforces Round 944 (Div. 4) ›

CF 1971F - Circle Perimeter

CF 1971F - Circle Perimeter Rating: 1600 Tags: binary search, brute force, dfs and similar, geometry, implementation, math Solve time: 1m 31s Verified: yes Solution Problem Understanding We are looking at integer grid points on the plane, each point having coordinates $(x, y)$ where both values are integers. For each test case, a radius $r$ is given, and we need to count how many lattice points lie in a thin...

Practice › Codeforces Solutions › Codeforces Round 953 (Div. 2) ›

CF 1978F - Large Graph

CF 1978F - Large Graph Rating: 2400 Tags: data structures, dfs and similar, dsu, graphs, number theory, two pointers Solve time: 2m 31s Verified: no Solution Problem Understanding We are given an array of integers and asked to build a square matrix where each row is a cyclic right shift of the previous row. Then, we treat every element of the matrix as a vertex in a graph. Two vertices...

Practice › Codeforces Solutions › Codeforces Round 950 (Div. 3) ›

CF 1980G - Yasya and the Mysterious Tree

CF 1980G - Yasya and the Mysterious Tree Rating: 2300 Tags: bitmasks, data structures, dfs and similar, graphs, greedy, strings, trees Solve time: 2m 48s Verified: no Solution Problem Understanding We are given a tree with n vertices. Each edge in this tree has a weight. There are m queries of two types. The first type changes the effective weights of all edges by XORing them with a given number...

Practice › Codeforces Solutions › Codeforces Round 949 (Div. 2) ›

CF 1981D - Turtle and Multiplication

CF 1981D - Turtle and Multiplication Rating: 2400 Tags: constructive algorithms, dfs and similar, graphs, number theory Solve time: 2m 46s Verified: no Solution Problem Understanding We need to construct an array of length n such that every adjacent product is unique. More precisely, the values $$a_1a_2,\ a_2a_3,\ \dots,\ a_{n-1}a_n$$ must all be different. Among all arrays satisfying this condition, we want to minimize the number of distinct values appearing...

Practice › Codeforces Solutions › Codeforces Round 952 (Div. 4) ›

CF 1985H1 - Maximize the Largest Component (Easy Version)

CF 1985H1 - Maximize the Largest Component (Easy Version) Rating: 1700 Tags: brute force, data structures, dfs and similar, dsu, graphs, implementation Solve time: 2m 32s Verified: no Solution Problem Understanding We are given a grid consisting of n rows and m columns, where each cell is either empty ('.') or filled ('#'). A connected component of filled cells is a set of '#' tiles where you can move between...

Practice › Codeforces Solutions › Codeforces Round 952 (Div. 4) ›

CF 1985H2 - Maximize the Largest Component (Hard Version)

CF 1985H2 - Maximize the Largest Component (Hard Version) Rating: 2200 Tags: data structures, dfs and similar, dp, dsu, implementation Solve time: 2m 13s Verified: no Solution Problem Understanding We are given a grid of size $n \times m$ where each cell is either empty ('.') or filled ('#'). Connected components of '#' are sets of cells that can reach each other by moving up, down, left, or right. Alex...

Practice › Codeforces Solutions › Codeforces Round 954 (Div. 3) ›

CF 1986F - Non-academic Problem

CF 1986F - Non-academic Problem Rating: 1900 Tags: dfs and similar, graphs, trees Solve time: 1m 12s Verified: yes Solution Problem Understanding We are given a connected undirected graph. Between any two vertices, we can ask whether there is a path connecting them. If a path exists, that pair contributes to the final answer. Because the graph is connected initially, every pair of vertices is reachable, so initially all $\frac{n(n-1)}{2}$...

Practice › Codeforces Solutions › EPIC Institute of Technology Round Summer 2024 (Div. 1 + Div. 2) ›

CF 1987E - Wonderful Tree!

CF 1987E - Wonderful Tree! Rating: 2000 Tags: brute force, data structures, dfs and similar, dsu, greedy, trees Solve time: 2m 2s Verified: yes Solution Problem Understanding We are given a rooted tree with integer values assigned to each node. The tree is rooted at vertex 1. A tree is considered wonderful if, for every non-leaf vertex, its value is at most the sum of the values of its immediate...

Practice › Codeforces Solutions › Codeforces Round 958 (Div. 2) ›

CF 1988D - The Omnipotent Monster Killer

CF 1988D - The Omnipotent Monster Killer Rating: 2000 Tags: brute force, dfs and similar, dp, trees Solve time: 3m 29s Verified: yes Solution Problem Understanding We are given a tree with n vertices, where each vertex holds a monster with a certain attack power. You, the monster killer, face the monsters for effectively an infinite number of rounds. In each round, all living monsters deal damage to you equal...

Practice › Codeforces Solutions › Educational Codeforces Round 167 (Rated for Div. 2) ›

CF 1989F - Simultaneous Coloring

CF 1989F - Simultaneous Coloring Rating: 3000 Tags: dfs and similar, divide and conquer, graphs Solve time: 3m 1s Verified: no Solution Problem Understanding We are given a matrix with n rows and m columns, initially colorless. The allowed operations are painting an entire row red or an entire column blue. Multiple operations can be applied simultaneously, but the cost is quadratic in the number of simultaneous operations: performing k...

Practice › Codeforces Solutions › Codeforces Round 960 (Div. 2) ›

CF 1990E2 - Catch the Mole(Hard Version)

CF 1990E2 - Catch the Mole(Hard Version) Rating: 2600 Tags: binary search, data structures, dfs and similar, divide and conquer, interactive, trees Solve time: 2m 21s Verified: no Solution Problem Understanding We are working with a rooted tree where node 1 is fixed as the root. Somewhere in this tree there is a hidden token, called the mole, which occupies a single node. We do not know its position initially,...

Practice › Codeforces Solutions › Codeforces Round 960 (Div. 2) ›

CF 1990E1 - Catch the Mole(Easy Version)

CF 1990E1 - Catch the Mole(Easy Version) Rating: 2500 Tags: binary search, data structures, dfs and similar, interactive, trees Solve time: 2m 4s Verified: no Solution Problem Understanding We are working with a rooted tree where node 1 is the root, and one hidden token, the “mole”, starts at some unknown node. We cannot observe its position directly. Instead, we interact with the tree using queries on nodes. A query...

Practice › Codeforces Solutions › Pinely Round 4 (Div. 1 + Div. 2) ›

CF 1991E - Coloring Game

CF 1991E - Coloring Game Rating: 1900 Tags: constructive algorithms, dfs and similar, games, graphs, greedy, interactive Solve time: 3m 7s Verified: no Solution Problem Understanding We are asked to play a two-player game on a connected undirected graph where each vertex can be colored with one of three colors. The game proceeds in rounds equal to the number of vertices. In each round, the player Alice chooses two distinct...

Practice › Codeforces Solutions › Educational Codeforces Round 168 (Rated for Div. 2) ›

CF 1997D - Maximize the Root

CF 1997D - Maximize the Root Rating: 1500 Tags: binary search, dfs and similar, dp, greedy, trees Solve time: 2m 36s Verified: yes Solution Problem Understanding We are given a rooted tree. Every vertex contains a non-negative number. An operation can be applied to any non-leaf vertex. When we choose a vertex $v$, we increase the value at $v$ by one and simultaneously decrease every other vertex in the subtree...

Practice › Codeforces Solutions ›

Codeforces Round 967 (Div. 2)

Codeforces Round 967 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 2/6 | Rating range: 800-2900 | Time: 20m 15s Problem Name Rating Tags Solve Time Verified A Make All Equal 800 greedy, implementation 8m 5s ✓ B Generate Permutation 800 constructive-algorithms 3m 18s ✓ C Guess The Tree 1500 binary-search, brute-force, dfs-and-similar 3m 35s ✗ D Longest Max Min Subsequence 1900 brute-force, constructive-algorithms, data-structures 3m 20s ✗...

Practice › Codeforces Solutions › Codeforces Round 967 (Div. 2) ›

CF 2001C - Guess The Tree

CF 2001C - Guess The Tree Rating: 1500 Tags: binary search, brute force, dfs and similar, divide and conquer, dsu, greedy, interactive, trees Solve time: 3m 35s Verified: no Solution Problem Understanding We are asked to reconstruct a hidden tree with n nodes by interacting with a judge that answers specific distance-based queries. Each query "? a b" returns the node x that minimizes the absolute difference in distances from...

Practice › Codeforces Solutions › EPIC Institute of Technology Round August 2024 (Div. 1 + Div. 2) ›

CF 2002F1 - Court Blue (Easy Version)

CF 2002F1 - Court Blue (Easy Version) Rating: 2600 Tags: brute force, dfs and similar, dp, math, number theory Solve time: 2m 57s Verified: no Solution Problem Understanding We are asked to plan a match between two performers, Lelle and Flamm, where each round produces a winner. The goal is to maximize the total score, which is computed as l * W_L + f * W_F , where W_L and...

Practice › Codeforces Solutions › EPIC Institute of Technology Round August 2024 (Div. 1 + Div. 2) ›

CF 2002D2 - DFS Checker (Hard Version)

CF 2002D2 - DFS Checker (Hard Version) Rating: 2300 Tags: binary search, data structures, dfs and similar, graphs, hashing, trees Solve time: 2m 23s Verified: no Solution Problem Understanding We are given a rooted tree where vertex 1 is the root. Alongside the tree, we maintain a permutation stored in an array indexed by positions, and we repeatedly swap two positions in this array. After each swap, we must decide...

Practice › Codeforces Solutions › EPIC Institute of Technology Round August 2024 (Div. 1 + Div. 2) ›

CF 2002D1 - DFS Checker (Easy Version)

CF 2002D1 - DFS Checker (Easy Version) Rating: 1900 Tags: brute force, data structures, dfs and similar, graphs, hashing, trees Solve time: 1m 30s Verified: yes Solution Problem Understanding We are given a perfect binary tree whose vertices are numbered in heap order. Vertex 1 is the root, and for every vertex i > 1 , its parent is i // 2 . A permutation p of all vertices is...

Practice › Codeforces Solutions › Codeforces Round 968 (Div. 2) ›

CF 2003D2 - Turtle and a MEX Problem (Hard Version)

CF 2003D2 - Turtle and a MEX Problem (Hard Version) Rating: 2100 Tags: dfs and similar, dp, graphs, greedy, implementation, math Solve time: 2m 31s Verified: no Solution Problem Understanding The problem involves a turtle playing with several integer sequences and a non-negative integer $x$. For each sequence, the turtle can perform an operation exactly once: he sets $x$ to the $\text{mex}$ of its current value together with the numbers...

Practice › Codeforces Solutions ›

Codeforces Round 969 (Div. 1)

Codeforces Round 969 (Div. 1) Type: Div. 1 | Problems: 6 | Verified: 0/6 | Rating range: 1700-3500 | Time: 10m 11s Problem Name Rating Tags Solve Time Verified A Iris and Game on the Tree 1700 constructive-algorithms, dfs-and-similar, games 2m 11s ✗ B Iris and the Tree 1800 brute-force, data-structures, dfs-and-similar 1m 34s ✗ C Eri and Expanded Sets 2300 data-structures, divide-and-conquer, math 2m 53s ✗ D Iris and...

Practice › Codeforces Solutions › Codeforces Round 969 (Div. 1) ›

CF 2006E - Iris's Full Binary Tree

CF 2006E - Iris's Full Binary Tree Rating: 3100 Tags: brute force, data structures, dfs and similar, trees Solve time: 2m 7s Verified: no Solution Problem Understanding We are building a tree incrementally, one node at a time. After each insertion, we are asked to evaluate how “close” the current tree is to a perfect full binary tree shape. A full binary tree of depth $d$ is extremely rigid: it...

Practice › Codeforces Solutions › Codeforces Round 969 (Div. 1) ›

CF 2006A - Iris and Game on the Tree

CF 2006A - Iris and Game on the Tree Rating: 1700 Tags: constructive algorithms, dfs and similar, games, graphs, greedy, trees Solve time: 2m 11s Verified: no Solution Problem Understanding We are given a rooted tree with root fixed at vertex 1. Each vertex carries a label that is either 0, 1, or unknown. The unknown entries are the only things we are allowed to choose during the game, and...

Practice › Codeforces Solutions › Codeforces Round 969 (Div. 1) ›

CF 2006B - Iris and the Tree

CF 2006B - Iris and the Tree Rating: 1800 Tags: brute force, data structures, dfs and similar, dsu, math, trees Solve time: 1m 34s Verified: no Solution Problem-Type Check This is a Type B (prove) problem. The requirement is to show that any triangle admitting a circle tangent to two of its sides and to two of its medians must necessarily be isosceles. The statement is exact and requires a...

Practice › Codeforces Solutions › Codeforces Round 974 (Div. 3) ›

CF 2014F - Sheriff's Defense

CF 2014F - Sheriff's Defense Rating: 2000 Tags: dfs and similar, dp, greedy, trees Solve time: 1m 47s Verified: no Solution Problem Understanding We are given a tree where each node represents a camp holding some amount of gold. We may choose certain camps to “strengthen”. Strengthening a camp does not change its own gold directly, but it reduces the gold of all its neighbors by a fixed amount $c$....

Practice › Codeforces Solutions › Codeforces Round 974 (Div. 3) ›

CF 2014E - Rendez-vous de Marian et Robin

CF 2014E - Rendez-vous de Marian et Robin Rating: 1800 Tags: dfs and similar, graphs, shortest paths Solve time: 1m 14s Verified: yes Solution Problem Understanding We are working on a weighted undirected graph where two people start from opposite ends and want to meet as quickly as possible. One starts at vertex 1 and the other at vertex n. They move along edges, but there is a twist: some...

Practice › Codeforces Solutions › Codeforces Round 975 (Div. 1) ›

CF 2018C - Tree Pruning

CF 2018C - Tree Pruning Rating: 1700 Tags: brute force, dfs and similar, greedy, sortings, trees Solve time: 1m 55s Verified: yes Solution Problem Understanding We are given a tree rooted at node 1, and we can remove leaves one by one along with their connecting edges. The goal is to make all remaining leaves equidistant from the root. A leaf is any node with degree 1 that is not...

Practice › Codeforces Solutions › Codeforces Round 977 (Div. 2, based on COMPFEST 16 - Final Round) ›

CF 2021E3 - Digital Village (Extreme Version)

CF 2021E3 - Digital Village (Extreme Version) Rating: 2800 Tags: data structures, dfs and similar, dp, dsu, graphs, greedy, math, trees Solve time: 1m 48s Verified: no Solution Problem Understanding We are given a connected village represented as a graph. Each node is a house, and edges are internet cables with a latency weight. Some subset of houses specifically need internet. We are allowed to install servers in up to...

Practice › Codeforces Solutions › Codeforces Round 977 (Div. 2, based on COMPFEST 16 - Final Round) ›

CF 2021E1 - Digital Village (Easy Version)

CF 2021E1 - Digital Village (Easy Version) Rating: 2300 Tags: brute force, data structures, dfs and similar, dp, dsu, fft, graphs, greedy, implementation, math, trees Solve time: 2m 17s Verified: yes Solution Problem Understanding In this problem, we are given a village represented as a connected graph with houses as nodes and internet cables as edges. Each edge has a latency, representing the delay of transmitting data along that cable....

Practice › Codeforces Solutions › Codeforces Round 978 (Div. 2) ›

CF 2022E1 - Billetes MX (Easy Version)

CF 2022E1 - Billetes MX (Easy Version) Rating: 2500 Tags: 2-sat, binary search, combinatorics, constructive algorithms, dfs and similar, dsu, graphs Solve time: 2m 6s Verified: no Solution Problem Understanding We are given a partially specified n × m grid. Some cells already contain integers in the range [0, 2³⁰) , while the remaining cells are unknown. A grid is called beautiful if every axis-aligned rectangle satisfies the XOR condition...

Practice › Codeforces Solutions › Codeforces Round 980 (Div. 1) ›

CF 2023C - C+K+S

CF 2023C - C+K+S Rating: 2400 Tags: constructive algorithms, dfs and similar, graphs, greedy, hashing, implementation, strings Solve time: 1m 49s Verified: no Solution Problem Understanding We are given two directed graphs, each with the same number of vertices. Each graph is already strongly connected, and every directed cycle inside each graph has length divisible by a fixed integer $k$. This already imposes a hidden structure on both graphs: they...

Practice › Codeforces Solutions › Educational Codeforces Round 171 (Rated for Div. 2) ›

CF 2026F - Bermart Ice Cream

CF 2026F - Bermart Ice Cream Rating: 2700 Tags: data structures, dfs and similar, divide and conquer, dp, implementation, trees Solve time: 1m 39s Verified: no Solution Problem Understanding We are managing a growing family of stores, where each store contains a multiset of ice cream types. Each type has two attributes: a cost and a tastiness value. Stores are not independent. Instead, they form a rooted cloning structure: a...

Practice › Codeforces Solutions › Educational Codeforces Round 171 (Rated for Div. 2) ›

CF 2026E - Best Subsequence

CF 2026E - Best Subsequence Rating: 2500 Tags: bitmasks, dfs and similar, flows, graph matchings, graphs Solve time: 1m 4s Verified: yes Solution Problem Understanding We are given several independent test cases. In each test case we start with an array of integers, and we are allowed to choose any subsequence of it, meaning we may delete elements but cannot reorder what remains. For any chosen subsequence, we compute a...

Practice › Codeforces Solutions › Codeforces Round 986 (Div. 2) ›

CF 2028E - Alice's Adventures in the Rabbit Hole

CF 2028E - Alice's Adventures in the Rabbit Hole Rating: 2300 Tags: combinatorics, dfs and similar, dp, games, greedy, math, probabilities, trees Solve time: 1m 23s Verified: no Solution Problem Understanding We are given a tree with n vertices where vertex 1 is considered the exit of the rabbit hole, and Alice starts at some vertex v . Each turn a fair coin is flipped. On heads, Alice chooses an...

Practice › Codeforces Solutions › Refact.ai Match 1 (Codeforces Round 985) ›

CF 2029D - Cool Graph

CF 2029D - Cool Graph Rating: 1900 Tags: constructive algorithms, data structures, dfs and similar, dsu, graphs, greedy, trees Solve time: 1m 37s Verified: no Solution Problem Understanding We are given a simple undirected graph with $n$ vertices and $m$ edges. The graph can be arbitrary but contains no self-loops or multiple edges. We are allowed to perform a "triangle flip" operation on any three distinct vertices $a$, $b$, $c$....

Practice › Codeforces Solutions › Codeforces Round 987 (Div. 2) ›

CF 2031E - Penchick and Chloe's Trees

CF 2031E - Penchick and Chloe's Trees Rating: 2100 Tags: data structures, dfs and similar, dp, greedy, implementation, math, sortings, trees Solve time: 2m 6s Verified: no Solution Problem Understanding The problem gives us a rooted tree constructed by Penchick with n vertices and asks us to determine the minimum depth d of a perfect binary tree that Chloe can construct, so that after performing a sequence of "node removal...

Practice › Codeforces Solutions › Codeforces Round 987 (Div. 2) ›

CF 2031D - Penchick and Desert Rabbit

CF 2031D - Penchick and Desert Rabbit Rating: 1700 Tags: binary search, data structures, dfs and similar, dp, dsu, greedy, implementation, two pointers Solve time: 1m 43s Verified: no Solution Problem Understanding We are given a line of trees, each with a height. A rabbit starts at some position and can move between trees using a very specific rule that depends on both position and height. From a tree at...

Practice › Codeforces Solutions › Codeforces Round 981 (Div. 3) ›

CF 2033G - Sakurako and Chefir

CF 2033G - Sakurako and Chefir Rating: 2200 Tags: data structures, dfs and similar, dp, greedy, trees Solve time: 1m 50s Verified: no Solution Problem Understanding We are asked to analyze movement on a rooted tree. The tree has $n$ vertices, with vertex $1$ as the root. Chefir, starting at a given vertex $v_i$, has a limited stamina $k_i$. Movement rules are asymmetric: moving from a vertex to any descendant...

Practice › Codeforces Solutions › Codeforces Round 981 (Div. 3) ›

CF 2033E - Sakurako, Kosuke, and the Permutation

CF 2033E - Sakurako, Kosuke, and the Permutation Rating: 1400 Tags: brute force, data structures, dfs and similar, dsu, graphs, greedy, math Solve time: 1m 18s Verified: yes Solution Problem Understanding We are given a permutation of numbers from 1 to n. We are allowed to repeatedly swap any two positions. After performing some swaps, we want the permutation to satisfy a structural condition on every index i. At each...

Practice › Codeforces Solutions › Rayan Programming Contest 2024 - Selection (Codeforces Round 989, Div. 1 + Div. 2) ›

CF 2034H - Rayan vs. Rayaneh

CF 2034H - Rayan vs. Rayaneh Rating: 3300 Tags: brute force, dfs and similar, dp, number theory Solve time: 2m 31s Verified: no Solution Problem Understanding We are given a set of distinct positive integers. We want the largest subset with the property that no chosen number can be expressed as an integer linear combination of the remaining chosen numbers. For integers, the subgroup generated by a collection of numbers...

Practice › Codeforces Solutions › Rayan Programming Contest 2024 - Selection (Codeforces Round 989, Div. 1 + Div. 2) ›

CF 2034C - Trapped in the Witch's Labyrinth

CF 2034C - Trapped in the Witch's Labyrinth Rating: 1400 Tags: constructive algorithms, dfs and similar, graphs, implementation Solve time: 3m 10s Verified: yes Solution Problem Understanding We are given a grid where each cell either forces movement in one of four directions or is still undecided. Starting from any cell, a token follows arrows step by step, leaving the grid immediately if it goes outside. Some cells may form...

Practice › Codeforces Solutions › Codeforces Global Round 27 ›

CF 2035F - Tree Operations

CF 2035F - Tree Operations Rating: 2500 Tags: binary search, brute force, dfs and similar, dp, trees Solve time: 2m 23s Verified: no Solution Problem Understanding We are given a rooted tree with n nodes, each carrying an initial nonnegative value. The task is to reduce all node values to zero using operations that are applied in a fixed cyclic order on the nodes: the first n operations are applied...

Practice › Codeforces Solutions › Atto Round 1 (Codeforces Round 1041, Div. 1 + Div. 2) ›

CF 2127E - Ancient Tree

CF 2127E - Ancient Tree Rating: 2100 Tags: constructive algorithms, data structures, dfs and similar, dsu, greedy, trees Solve time: 2m 24s Verified: no Solution Problem Understanding We are given a rooted tree with weighted vertices, where each vertex either has a fixed color between 1 and k or a missing color represented by 0. The goal is to assign colors to all uncolored vertices to minimize the total weight...

Practice › Codeforces Solutions › Atto Round 1 (Codeforces Round 1041, Div. 1 + Div. 2) ›

CF 2127D - Root was Built by Love, Broken by Destiny

CF 2127D - Root was Built by Love, Broken by Destiny Rating: 1800 Tags: combinatorics, dfs and similar, graphs, trees Solve time: 1m 52s Verified: no Solution Problem Understanding We are given a connected undirected graph of n houses and m bridges. Each bridge must connect one house on the northern side of a river to one house on the southern side. Houses must be placed along straight lines on...

Practice › Codeforces Solutions › Codeforces Round 1029 (Div. 3) ›

CF 2117F - Wildflower

CF 2117F - Wildflower Rating: 1800 Tags: combinatorics, dfs and similar, trees Solve time: 3m 8s Verified: no Solution Problem Understanding We are given a rooted tree where vertex 1 is the root, and every node must be assigned a value either 1 or 2. Once these values are fixed, every node computes a quantity defined as the sum of values in its rooted subtree, meaning the node itself plus...

Practice › Codeforces Solutions ›

Codeforces Round 1028 (Div. 1)

Codeforces Round 1028 (Div. 1) Type: Div. 1 | Problems: 7 | Verified: 3/7 | Rating range: 1500-3500 | Time: 12m 1s Problem Name Rating Tags Solve Time Verified A Gellyfish and Flaming Peony 1500 constructive-algorithms, dp, math 1m 17s ✓ B Gellyfish and Camellia Japonica 2100 brute-force, constructive-algorithms, dfs-and-similar 1m 56s ✗ C Gellyfish and Eternal Violet 2700 combinatorics, dp, greedy 1m 48s ✗ D Gellyfish and Forget-Me-Not 2900...

Practice › Codeforces Solutions › Codeforces Round 1028 (Div. 1) ›

CF 2115B - Gellyfish and Camellia Japonica

CF 2115B - Gellyfish and Camellia Japonica Rating: 2100 Tags: brute force, constructive algorithms, dfs and similar, dp, graphs, greedy, trees Solve time: 1m 56s Verified: no Solution Problem Understanding We are given a final array b that results from a sequence of q operations on an initial array a . Each operation selects two positions x and y , takes the minimum of their current values, and assigns it...

Practice › Codeforces Solutions › Codeforces Round 1021 (Div. 1) ›

CF 2097E - Clearing the Snowdrift

CF 2097E - Clearing the Snowdrift Rating: 3100 Tags: data structures, dfs and similar, dp, greedy Solve time: 1m 39s Verified: yes Solution Problem Understanding We are given a runway divided into n sections, each covered with some snow. The snow in the i -th section has height a_i . A snowplow can operate on any contiguous segment of at most length d . When it operates, it removes exactly...

Practice › Codeforces Solutions ›

Codeforces Round 1021 (Div. 1)

Codeforces Round 1021 (Div. 1) Type: Div. 1 | Problems: 6 | Verified: 2/6 | Rating range: 1400-3500 | Time: 9m 51s Problem Name Rating Tags Solve Time Verified A Sports Betting 1400 2-sat, brute-force, math 1m 32s ✗ B Baggage Claim 2300 combinatorics, dfs-and-similar, dp 2m 8s ✗ C Bermuda Triangle 2400 chinese-remainder-theorem, geometry, implementation 1m 42s ✗ D Homework 2800 bitmasks, math, matrices 1m 42s ✗ E Clearing...

Practice › Codeforces Solutions › Codeforces Round 1021 (Div. 1) ›

CF 2097B - Baggage Claim

CF 2097B - Baggage Claim Rating: 2300 Tags: combinatorics, dfs and similar, dp, dsu, graphs, implementation, math, trees Solve time: 2m 8s Verified: no Solution Problem Understanding The task is to reconstruct a simple path on a rectangular grid where only the cells with odd indices are known. Specifically, the path alternates between "known" and "unknown" cells, starting and ending with known cells. Each consecutive pair of cells in the...

Practice › Codeforces Solutions ›

Codeforces Round 998 (Div. 3)

Codeforces Round 998 (Div. 3) Type: Div. 3 | Problems: 7 | Verified: 4/7 | Rating range: 800-2400 | Time: 11m 10s Problem Name Rating Tags Solve Time Verified A Fibonacciness 800 brute-force 1m 5s ✓ B Farmer John's Card Game 1000 greedy, sortings 1m 21s ✓ C Game of Mathletes 900 games, greedy, sortings 1m 18s ✓ D Subtract Min Sort 1100 greedy 1m 48s ✗ E Graph Composition...

Practice › Codeforces Solutions › Codeforces Round 998 (Div. 3) ›

CF 2060E - Graph Composition

CF 2060E - Graph Composition Rating: 1500 Tags: dfs and similar, dsu, graphs, greedy Solve time: 1m 14s Verified: yes Solution Problem Understanding We are given two undirected graphs on the same set of vertices. One graph, call it the working graph, is the structure we are allowed to modify. The second graph is a fixed reference structure that we must eventually “match” in terms of connectivity. The allowed operation...

Practice › Codeforces Solutions › Codeforces Round 992 (Div. 2) ›

CF 2040D - Non Prime Tree

CF 2040D - Non Prime Tree Rating: 1900 Tags: brute force, constructive algorithms, dfs and similar, greedy, number theory, trees, two pointers Solve time: 3m 17s Verified: no Solution Problem Understanding We are given a tree with $n$ vertices, and we must assign each vertex a distinct integer from the range $1$ to $2n$, using exactly $n$ of those numbers. The assignment is arbitrary except that every vertex gets a...

Practice › Codeforces Solutions › Codeforces Round 992 (Div. 2) ›

CF 2040E - Control of Randomness

CF 2040E - Control of Randomness Rating: 2100 Tags: combinatorics, dfs and similar, dp, graphs, greedy, math, probabilities, trees Solve time: 2m 6s Verified: no Solution Problem Understanding We are given a tree, an undirected connected acyclic graph, with n vertices rooted at vertex 1 . A robot starts at some vertex v ≠ 1 and moves toward the root. Odd-numbered steps are deterministic: the robot always moves one step...

Practice › Codeforces Solutions › 2024 ICPC Asia Taichung Regional Contest (Unrated, Online Mirror, ICPC Rules, Preferably Teams) ›

CF 2041K - Trophic Balance Species

CF 2041K - Trophic Balance Species Rating: 3100 Tags: binary search, brute force, dfs and similar, graphs Solve time: 1m 4s Verified: yes Solution Problem Understanding We are given an ecosystem modeled as a directed graph, where each node represents a species and each directed edge represents a feeding relationship from prey to predator. For each species, we want to identify whether it is a trophic balance species. A species...

Practice › Codeforces Solutions › 2024 ICPC Asia Taichung Regional Contest (Unrated, Online Mirror, ICPC Rules, Preferably Teams) ›

CF 2041D - Drunken Maze

CF 2041D - Drunken Maze Rating: 1700 Tags: brute force, dfs and similar, graphs, shortest paths Solve time: 3m 24s Verified: yes Solution Problem Understanding We have a rectangular maze represented as a grid of characters. Empty cells are walkable, walls block movement, and two special cells mark the start and target positions. The goal is to reach the target from the start in the minimum number of steps, moving...

Practice › Codeforces Solutions › 2024 ICPC Asia Taichung Regional Contest (Unrated, Online Mirror, ICPC Rules, Preferably Teams) ›

CF 2041F - Segmentation Folds

CF 2041F - Segmentation Folds Rating: 2400 Tags: brute force, dfs and similar, number theory Solve time: 1m 41s Verified: no Solution Problem Understanding We are given a segment on the number line defined by two integers $\ell$ and $r$, and Peter can fold this segment in two specific ways: from left to right ( LTR ) and from right to left ( RTL ). Each fold is only possible...

Practice › Codeforces Solutions › 2024 ICPC Asia Taichung Regional Contest (Unrated, Online Mirror, ICPC Rules, Preferably Teams) ›

CF 2041C - Cube

CF 2041C - Cube Rating: 2000 Tags: bitmasks, dfs and similar, dp Solve time: 1m 16s Verified: yes Solution Problem Understanding We are given a cube of size $n \times n \times n$, where every cell contains a weight. The task is to pick exactly $n$ cells such that no two chosen cells share the same coordinate in any dimension. In other words, if we think of a chosen set...

Practice › Codeforces Solutions › Educational Codeforces Round 172 (Rated for Div. 2) ›

CF 2042E - Vertex Pairs

CF 2042E - Vertex Pairs Rating: 2900 Tags: binary search, brute force, data structures, dfs and similar, divide and conquer, greedy, implementation, trees Solve time: 2m 4s Verified: no Solution The failure you show is not enough to diagnose the algorithm itself. Let's trace what happened: The input contains 5 test cases : 5 2 2 1 5 2 3 4 5 1 5 2 1 4 2 3 5...

Practice › Codeforces Solutions › Educational Codeforces Round 173 (Rated for Div. 2) ›

CF 2043E - Matrix Transformation

CF 2043E - Matrix Transformation Rating: 2300 Tags: bitmasks, brute force, data structures, dfs and similar, graphs, greedy, implementation Solve time: 2m 10s Verified: no Solution The failure you show is not enough to diagnose the algorithm itself. Let's trace what happened: The input contains 5 test cases : 5 2 2 1 5 2 3 4 5 1 5 2 1 4 2 3 5 4 1 1 5...

Practice › Codeforces Solutions › Codeforces Round 993 (Div. 4) ›

CF 2044G2 - Medium Demon Problem (hard version)

CF 2044G2 - Medium Demon Problem (hard version) Rating: 1900 Tags: dfs and similar, dp, dsu, graphs, implementation, trees Solve time: 2m 50s Verified: no Solution The error in your Python solution is a simple syntax mistake: the map(int, input().split()) call for reading b is missing a closing parenthesis. This prevents the code from running at all. Once that is fixed, the solution logic itself can remain the same. Here...

Practice › Codeforces Solutions › Codeforces Round 993 (Div. 4) ›

CF 2044G1 - Medium Demon Problem (easy version)

CF 2044G1 - Medium Demon Problem (easy version) Rating: 1700 Tags: dfs and similar, graph matchings, graphs, implementation, trees Solve time: 2m 24s Verified: yes Solution Problem Understanding Each spider chooses exactly one recipient. We can view this as a directed graph where every vertex has out-degree exactly one. Initially every spider owns one plushie. During a year, every spider that currently has a plushie sends one plushie along its...

Practice › Codeforces Solutions › 2024-2025 ICPC Asia Jakarta Regional Contest (Unrated, Online Mirror, ICPC Rules, Teams Preferred) ›

CF 2045M - Mirror Maze

CF 2045M - Mirror Maze Rating: 1800 Tags: brute force, dfs and similar, graphs, implementation Solve time: 1m 34s Verified: yes Solution Problem Understanding Think of the laser beam as moving along the grid lines between cells. Whenever the beam enters a cell through one side, the content of that cell determines which side it leaves from. An empty cell does not change direction. A / mirror turns the beam...

Practice › Codeforces Solutions › Codeforces Round 991 (Div. 3) ›

CF 2050G - Tree Destruction

CF 2050G - Tree Destruction Rating: 1900 Tags: dfs and similar, dp, trees Solve time: 1m 13s Verified: yes Solution Problem Understanding We are given a tree, which is an acyclic connected graph, with $n$ vertices. The task is to select two vertices, $a$ and $b$, and remove all vertices along the unique path between them, including $a$ and $b$ themselves. After this removal, the tree splits into one or...

Practice › Codeforces Solutions › Good Bye 2024: 2025 is NEAR ›

CF 2053E - Resourceful Caterpillar Sequence

CF 2053E - Resourceful Caterpillar Sequence Rating: 1900 Tags: dfs and similar, dp, games, graphs, greedy, trees Solve time: 1m 48s Verified: no Solution Problem Understanding We are given a tree. Two endpoints are chosen, a head $p$ and a tail $q$, and the only vertices that matter are those on the unique path between them. The game is a two-player process where Nora controls the head side and Aron...

Practice › Codeforces Solutions › Codeforces Round 997 (Div. 2) ›

CF 2056E - Nested Segments

CF 2056E - Nested Segments Rating: 2500 Tags: combinatorics, dfs and similar, dp, dsu, math Solve time: 1m 54s Verified: no Solution Problem Understanding We are given a set of integer segments over the range [1, n] . Each segment is a closed interval [l, r] . The initial set of segments, S , is "good", meaning that for any two distinct segments in the set, either they do not...

Practice › Codeforces Solutions › Codeforces Round 997 (Div. 2) ›

CF 2056B - Find the Permutation

CF 2056B - Find the Permutation Rating: 1300 Tags: brute force, dfs and similar, graphs, implementation, sortings Solve time: 3m 24s Verified: no Solution Problem Understanding We are given an undirected graph whose structure is secretly generated from a hidden permutation of the vertices. Each vertex label from 1 to n corresponds to one position in that permutation, and the edges encode pairwise ordering information: whenever two positions i and...

Practice › Codeforces Solutions › Hello 2025 ›

CF 2057E2 - Another Exercise on Graphs (hard version)

CF 2057E2 - Another Exercise on Graphs (hard version) Rating: 2500 Tags: binary search, dfs and similar, dp, dsu, graphs, shortest paths, sortings Solve time: 3m 55s Verified: no Solution Problem Understanding We are given an undirected weighted graph and a large number of queries. Each query picks two vertices and an integer k , and asks us to consider all possible paths between those vertices. Among all such paths,...

Practice › Codeforces Solutions › Hello 2025 ›

CF 2057G - Secret Message

CF 2057G - Secret Message Rating: 3000 Tags: constructive algorithms, dfs and similar, math Solve time: 1m 41s Verified: no Solution Problem Understanding The problem gives a rectangular grid where some cells are already blocked and cannot be used. The free cells, marked with "#", form a figure on the grid. We are asked to choose a subset of free cells, denoted as S , such that every free cell...

Practice › Codeforces Solutions › Ethflow Round 1 (Codeforces Round 1001, Div. 1 + Div. 2) ›

CF 2062E2 - The Game (Hard Version)

CF 2062E2 - The Game (Hard Version) Rating: 3000 Tags: data structures, dfs and similar, games, graphs, implementation, trees Solve time: 1m 38s Verified: no Solution Problem Understanding We are given a tree with n nodes rooted at node 1 , and each node has an associated integer weight. Cirno and Daiyousei play a sequential game on this tree. On her turn, a player selects a node that has a...

Practice › Codeforces Solutions › Ethflow Round 1 (Codeforces Round 1001, Div. 1 + Div. 2) ›

CF 2062E1 - The Game (Easy Version)

CF 2062E1 - The Game (Easy Version) Rating: 2000 Tags: data structures, dfs and similar, games, graphs, greedy, trees Solve time: 1m 55s Verified: no Solution Problem Understanding We are given a rooted tree where each node has a weight. Two players play a turn-based game. On each move, a player chooses a node whose weight is strictly larger than the weight chosen in the previous move and deletes its...

Practice › Codeforces Solutions › Ethflow Round 1 (Codeforces Round 1001, Div. 1 + Div. 2) ›

CF 2062D - Balanced Tree

CF 2062D - Balanced Tree Rating: 2200 Tags: dfs and similar, dp, graphs, greedy, trees Solve time: 1m 57s Verified: no Solution Problem Understanding We are given a rooted tree where each node has a range of allowable values [l_i, r_i] . Initially, each node can be assigned any value within its range. The goal is to make the tree balanced, meaning all nodes have the same final value. The...

Practice › Codeforces Solutions › Codeforces Round 1000 (Div. 2) ›

CF 2063F2 - Counting Is Not Fun (Hard Version)

CF 2063F2 - Counting Is Not Fun (Hard Version) Rating: 2700 Tags: combinatorics, data structures, dfs and similar, dsu, graphs, implementation, trees Solve time: 1m 43s Verified: no Solution Problem Understanding We are given a hidden balanced bracket sequence of length $2n$. The structure of the sequence is not arbitrary: it can be fully described by a set of $n$ disjoint “matching events”, where each event connects an opening bracket...

Practice › Codeforces Solutions › Codeforces Round 1000 (Div. 2) ›

CF 2063E - Triangle Tree

CF 2063E - Triangle Tree Rating: 2300 Tags: data structures, dfs and similar, dp, greedy, trees Solve time: 2m 35s Verified: no Solution Problem Understanding We are given a rooted tree with root at vertex 1 . For every unordered pair of vertices (u, v) , we only care about pairs where neither vertex is an ancestor of the other. Let a = dist(u, lca(u,v)) b = dist(v, lca(u,v)) Since...

Practice › Codeforces Solutions › Codeforces Round 1000 (Div. 2) ›

CF 2063F1 - Counting Is Not Fun (Easy Version)

CF 2063F1 - Counting Is Not Fun (Easy Version) Rating: 2400 Tags: combinatorics, data structures, dfs and similar, dp, dsu, graphs, hashing, implementation, math, trees Solve time: 1m 55s Verified: no Solution Problem Understanding The problem asks us to count balanced bracket sequences under incremental constraints. We are given a balanced sequence of 2n brackets, but we do not know its content. The sequence can be viewed as a set...

Practice › Codeforces Solutions › Codeforces Round 1000 (Div. 2) ›

CF 2063C - Remove Exactly Two

CF 2063C - Remove Exactly Two Rating: 1600 Tags: brute force, data structures, dfs and similar, dp, graphs, greedy, sortings, trees Solve time: 1m 53s Verified: no Solution Problem Understanding The problem asks us to consider a tree of n vertices and determine the maximum number of connected components that can result after removing exactly two vertices. Removing a vertex in a tree disconnects it from its neighbors, effectively splitting...

Practice › Codeforces Solutions › Codeforces Round 1003 (Div. 4) ›

CF 2065F - Skibidus and Slay

CF 2065F - Skibidus and Slay Rating: 1700 Tags: data structures, dfs and similar, graphs, greedy, trees Solve time: 1m 13s Verified: yes Solution Problem Understanding The problem asks us to analyze a tree where each vertex has a number assigned to it, and for every number from 1 to n, we must decide if there exists a simple path in the tree where that number is the majority. A...

Practice › Codeforces Solutions › Codeforces Round 1004 (Div. 2) ›

CF 2067C - Devyatkino

CF 2067C - Devyatkino Rating: 1500 Tags: brute force, dfs and similar, greedy, math Solve time: 1m 38s Verified: yes Solution Problem Understanding The problem gives us a positive integer n , and allows us to perform an operation where we add any number that consists entirely of the digit 9 repeated one or more times. Our goal is to make n contain at least one digit 7 using the...

Practice › Codeforces Solutions › European Championship 2025 - Online Mirror (Unrated, ICPC Rules, Teams Preferred) ›

CF 2068E - Porto Vs. Benfica

CF 2068E - Porto Vs. Benfica Rating: 2800 Tags: data structures, dfs and similar, dsu, graphs, shortest paths Solve time: 1m 44s Verified: no Solution Problem Understanding We are given a large undirected, unweighted graph representing a road network. One vertex is the starting point (Lisbon, vertex 1) and another is the destination (Porto, vertex n). A group of travelers always wants to reach the destination using as few edges...

Practice › Codeforces Solutions › Educational Codeforces Round 174 (Rated for Div. 2) ›

CF 2069F - Graph Inclusion

CF 2069F - Graph Inclusion Rating: 2800 Tags: data structures, dfs and similar, divide and conquer, dsu, graphs Solve time: 1m 48s Verified: no Solution Problem Understanding We are given two undirected graphs, $A$ and $B$, on the same set of $n$ vertices. Initially, both graphs have no edges. Queries arrive one by one; each query either toggles an edge in $A$ or $B$. After every query, we are asked:...

Practice › Codeforces Solutions › Educational Codeforces Round 175 (Rated for Div. 2) ›

CF 2070D - Tree Jumps

CF 2070D - Tree Jumps Rating: 1600 Tags: dfs and similar, dp, trees Solve time: 1m 34s Verified: yes Solution Problem Understanding We are asked to count the number of sequences of vertices in a rooted tree such that we can "jump" a chip along them according to specific rules. The tree has n vertices numbered from 1 to n with 1 as the root. Each vertex x has a...

Practice › Codeforces Solutions › Codeforces Round 1007 (Div. 2) ›

CF 2071C - Trapmigiano Reggiano

CF 2071C - Trapmigiano Reggiano Rating: 1700 Tags: constructive algorithms, data structures, dfs and similar, dp, greedy, sortings, trees Solve time: 2m 14s Verified: no Solution Problem Understanding We are given a tree, a starting vertex st , and a target vertex en . A permutation of all vertices must be chosen. During the i -th step, a piece of cheese appears at vertex p[i] . If the mouse is...

Practice › Codeforces Solutions › Codeforces Round 1008 (Div. 1) ›

CF 2077G - RGB Walking

CF 2077G - RGB Walking Rating: 3500 Tags: bitmasks, chinese remainder theorem, dfs and similar, graphs, number theory Solve time: 47s Verified: yes Solution Problem Understanding The problem gives a connected graph with n vertices and m edges. Each edge has three pieces of information: its endpoints, a positive integer weight no larger than x , and a color which is either red, green, or blue. The task is to...

Practice › Codeforces Solutions › Educational Codeforces Round 177 (Rated for Div. 2) ›

CF 2086E - Zebra-like Numbers

CF 2086E - Zebra-like Numbers Rating: 2400 Tags: bitmasks, brute force, constructive algorithms, dfs and similar, dp, greedy, math Solve time: 2m 8s Verified: yes Solution Problem Understanding A zebra-like number is a positive integer whose binary representation looks like 1 , 101 , 10101 , 1010101 , ... In other words, the bits alternate and the least significant bit is 1 . Let $$z_1=1,\quad z_2=5,\quad z_3=21,\quad z_4=85,\dots$$ These are...

Practice › Codeforces Solutions › Educational Codeforces Round 177 (Rated for Div. 2) ›

CF 2086C - Disappearing Permutation

CF 2086C - Disappearing Permutation Rating: 1300 Tags: dfs and similar, dp, dsu, graphs, greedy, implementation Solve time: 1m 57s Verified: no Solution Problem Understanding We are given a permutation of integers from 1 to n, which means every number in that range appears exactly once in an array of size n. We then perform a sequence of queries, where in each query we replace a specific element of the...

Practice › Codeforces Solutions › Codeforces Round 1016 (Div. 3) ›

CF 2093G - Shorten the Array

CF 2093G - Shorten the Array Rating: 1900 Tags: binary search, bitmasks, data structures, dfs and similar, greedy, strings, trees, two pointers Solve time: 1m 45s Verified: no Solution Problem Understanding We are asked to find the shortest subarray of a given array a whose "beauty" reaches or exceeds a threshold k . The beauty of an array is the maximum XOR value between any pair of its elements. So...

Practice › Codeforces Solutions › Codeforces Round 1019 (Div. 2) ›

CF 2103D - Local Construction

CF 2103D - Local Construction Rating: 2000 Tags: constructive algorithms, dfs and similar, implementation, two pointers Solve time: 41s Verified: no Solution Problem Understanding We are given, for each position in an unknown permutation, the iteration at which the element at that position disappears under a deterministic pruning process. The permutation is repeatedly filtered: on odd iterations we keep only local minima, and on even iterations we keep only local...

Practice › Codeforces Solutions › Educational Codeforces Round 178 (Rated for Div. 2) ›

CF 2104F - Numbers and Strings

CF 2104F - Numbers and Strings Rating: 2600 Tags: binary search, brute force, dfs and similar, dp, implementation, math Solve time: 1m 45s Verified: no Solution Problem Understanding We are asked to count the number of distinct strings generated by a simple, but slightly tricky rule. For each integer $x$ from 1 up to $n$, we form a string by concatenating $x$ and $x+1$, then sorting the digits of this...

Practice › Codeforces Solutions › Codeforces Round 1020 (Div. 3) ›

CF 2106G2 - Baudelaire (hard version)

CF 2106G2 - Baudelaire (hard version) Rating: 2500 Tags: binary search, dfs and similar, divide and conquer, implementation, interactive, trees Solve time: 1m 38s Verified: no Solution Problem Understanding We are given a tree with up to 1000 nodes, and each node hides a value of either 1 or −1. The tree is rooted somewhere, but the root is unknown to us. What makes this unusual is that the root...

Practice › Codeforces Solutions › Codeforces Round 1020 (Div. 3) ›

CF 2106F - Goblin

CF 2106F - Goblin Rating: 1900 Tags: dfs and similar, dp, dsu, greedy, math Solve time: 2m 41s Verified: no Solution Problem Understanding We are asked to find the largest connected set of zeros in an $n \times n$ grid that is built from a single binary string $s$. Each row of the grid is generated by flipping one character of $s$ at the row's index. In other words, row...

Practice › Codeforces Solutions › Codeforces Round 1023 (Div. 2) ›

CF 2107D - Apple Tree Traversing

CF 2107D - Apple Tree Traversing Rating: 2100 Tags: brute force, dfs and similar, greedy, implementation, trees Solve time: 1m 32s Verified: no Solution Problem Understanding We are given a tree with n nodes, each node initially containing one apple. Our goal is to traverse this tree and repeatedly select paths consisting only of nodes that still have apples, remove the apples along that path, and write down three numbers:...

Practice › Codeforces Solutions › Codeforces Round 1022 (Div. 2) ›

CF 2108E - Spruce Dispute

CF 2108E - Spruce Dispute Rating: 2600 Tags: constructive algorithms, dfs and similar, graphs, greedy, implementation, shortest paths, trees Solve time: 1m 42s Verified: no Solution Problem Understanding We are given a tree with an odd number of vertices. Almost all vertices carry ornaments, and every ornament belongs to exactly one color, with each color appearing on exactly two vertices. One vertex is special and initially uncolored, acting as a...

Practice › Codeforces Solutions › Codeforces Round 1025 (Div. 2) ›

CF 2109F - Penguin Steps

CF 2109F - Penguin Steps Rating: 3000 Tags: binary search, dfs and similar, flows, graphs, shortest paths Solve time: 2m 5s Verified: no Solution Problem Understanding We are working on an $n \times n$ grid where each cell has two attributes: a weight $a_{i,j}$ and a color that is either black or white. Two players start from different positions on the left side of the grid and both aim to...

Practice › Codeforces Solutions › Codeforces Round 1025 (Div. 2) ›

CF 2109D - D/D/D

CF 2109D - D/D/D Rating: 1900 Tags: dfs and similar, graphs, greedy, shortest paths Solve time: 1m 32s Verified: no Solution Problem Understanding We are given a connected, undirected graph with n vertices and m edges. There are no self-loops or multiple edges, so each edge connects two distinct vertices exactly once. Along with the graph, we are given a multiset A of positive integers, each representing a "move length."...

Practice › Codeforces Solutions › Codeforces Round 1026 (Div. 2) ›

CF 2110D - Fewer Batteries

CF 2110D - Fewer Batteries Rating: 1700 Tags: binary search, dfs and similar, dp, graphs, greedy, hashing Solve time: 1m 42s Verified: no Solution Problem Understanding We are asked to guide a robot through a series of checkpoints. Each checkpoint has a certain number of batteries that the robot can collect, and there are one-way passages connecting some checkpoints. Each passage requires the robot to carry at least a certain...

Practice › Codeforces Solutions › Codeforces Round 1026 (Div. 2) ›

CF 2110E - Melody

CF 2110E - Melody Rating: 2300 Tags: dfs and similar, graphs, implementation Solve time: 1m 28s Verified: no Solution Problem Understanding We are asked to arrange a set of sounds, each defined by a volume and pitch, into a sequence that is simultaneously beautiful and non-boring. Beautiful means that consecutive sounds differ in exactly one dimension: either volume changes while pitch remains constant, or pitch changes while volume remains constant....

Practice › Codeforces Solutions › Educational Codeforces Round 180 (Rated for Div. 2) ›

CF 2112E - Tree Colorings

CF 2112E - Tree Colorings Rating: 2200 Tags: combinatorics, dfs and similar, dp, graphs, math, number theory, trees Solve time: 1m 40s Verified: no Solution Problem Understanding We are given a rooted tree, and every vertex must be assigned one of three colors: green, blue, or yellow. The root is fixed to be green. A coloring is considered valid when two connectivity constraints hold. If we look only at green...

Practice › Codeforces Solutions › Educational Codeforces Round 180 (Rated for Div. 2) ›

CF 2112D - Reachability and Tree

CF 2112D - Reachability and Tree Rating: 1700 Tags: constructive algorithms, dfs and similar, graphs, trees Solve time: 1m 29s Verified: no Solution Problem Understanding We are asked to take an undirected tree and assign a direction to each edge so that the number of ordered vertex pairs $(u, v)$ where there is a directed path from $u$ to $v$ equals exactly $n$, the number of vertices. In other words,...

Practice › Codeforces Solutions › Codeforces Round 1031 (Div. 2) ›

CF 2113E - From Kazan with Love

CF 2113E - From Kazan with Love Rating: 2800 Tags: dfs and similar, graphs, implementation, trees Solve time: 1m 46s Verified: yes Solution Problem Understanding We are given a tree representing a city. Marat starts at vertex x at time 1 and wants to reach vertex y . Each day progresses in discrete time steps, and at each step he can either stay in place or move along one edge...

Practice › Codeforces Solutions › Codeforces Round 1031 (Div. 2) ›

CF 2113F - Two Arrays

CF 2113F - Two Arrays Rating: 2500 Tags: constructive algorithms, dfs and similar, graphs, math Solve time: 1m 29s Verified: no Solution Problem Understanding We are given two arrays, a and b , each containing n integers. We can swap elements between the arrays at the same index as many times as we like. The goal is to maximize the sum of the number of distinct elements in each array....

Practice › Codeforces Solutions › Codeforces Round 1027 (Div. 3) ›

CF 2114F - Small Operations

CF 2114F - Small Operations Rating: 2000 Tags: binary search, brute force, dfs and similar, dp, math, number theory, sortings Solve time: 1m 36s Verified: no Solution Problem Understanding We are given two integers, x and y , and an upper bound k . Our goal is to transform x into y using the fewest possible operations. Each operation allows us to multiply x by any integer a between 1...

Practice › Codeforces Solutions › Codeforces Round 1027 (Div. 3) ›

CF 2114E - Kirei Attacks the Estate

CF 2114E - Kirei Attacks the Estate Rating: 1400 Tags: dfs and similar, dp, greedy, trees Solve time: 1m 29s Verified: no Solution Problem Understanding We are given a rooted tree where vertex 1 is the root, and each vertex has a numeric value. For every vertex $v$, we consider the path going upward from $v$ to the root. Along that path, we form several alternating-sum expressions: we may stop...

Practice › Codeforces Solutions ›

Codeforces Round 1048 (Div. 2)

Codeforces Round 1048 (Div. 2) Type: Div. 2 | Problems: 7 | Verified: 1/7 | Rating range: 800-2600 | Time: 10m 7s Problem Name Rating Tags Solve Time Verified A Maple and Multiplication 800 greedy, math 1m 9s ✓ B Cake Collection 800 greedy 1m 38s ✗ C Cake Assignment 1100 bitmasks, constructive-algorithms, greedy 1m 5s ✗ D Antiamuny Wants to Learn Swap 1900 data-structures, greedy 1m 47s ✗ E1...

Practice › Codeforces Solutions › Codeforces Round 1030 (Div. 2) ›

CF 2118D1 - Red Light, Green Light (Easy version)

CF 2118D1 - Red Light, Green Light (Easy version) Rating: 1700 Tags: brute force, dfs and similar, dp, graphs, implementation, number theory Solve time: 1m 58s Verified: yes Solution Problem Understanding We have a one-dimensional strip of length up to $10^{15}$, along which certain cells contain traffic lights. Each light has a fixed period $k$ and a delay $d_i < k$, and it turns red at times $l \cdot k...

Practice › Codeforces Solutions › Codeforces Round 1030 (Div. 2) ›

CF 2118D2 - Red Light, Green Light (Hard version)

CF 2118D2 - Red Light, Green Light (Hard version) Rating: 2200 Tags: binary search, brute force, data structures, dfs and similar, dp, graphs, implementation, math, number theory Solve time: 1m 37s Verified: no Solution Problem Understanding We are asked to simulate motion along a one-dimensional strip of length up to $10^{15}$, where certain cells contain traffic lights with periodic red signals. Each traffic light has a fixed period $k$ and...

Practice › Codeforces Solutions › Codeforces Round 1035 (Div. 2) ›

CF 2119F - Volcanic Eruptions

CF 2119F - Volcanic Eruptions Rating: 3300 Tags: dfs and similar, dp, greedy, shortest paths, trees Solve time: 1m 54s Verified: no Solution Problem Understanding We are given a rooted tree where every node carries a value of either +1 or −1. A lava wave starts from the root and expands outward one edge per time unit, so at time t every node at distance at most t from the...

Practice › Codeforces Solutions ›

Codeforces Round 1021 (Div. 2)

Codeforces Round 1021 (Div. 2) Type: Div. 2 | Problems: 6 | Verified: 2/6 | Rating range: 800-2800 | Time: 11m 22s Problem Name Rating Tags Solve Time Verified A Vadim's Collection 800 brute-force, greedy 3m 14s ✓ B Sasha and the Apartment Purchase 1400 math, sortings 1m 5s ✓ C Sports Betting 1400 greedy, math, sortings 1m 24s ✗ D Baggage Claim 2300 combinatorics, dfs-and-similar, graphs 2m 45s ✗...

Practice › Codeforces Solutions › Codeforces Round 1037 (Div. 3) ›

CF 2126F - 1-1-1, Free Tree!

CF 2126F - 1-1-1, Free Tree! Rating: 2000 Tags: brute force, data structures, dfs and similar, graphs, implementation, trees Solve time: 1m 17s Verified: yes Solution Problem Understanding We are given a tree where every vertex has a color and every edge has a weight. An edge contributes its weight to the total cost only when its endpoints currently have different colors; if the endpoints share the same color, the...

Practice › Codeforces Solutions › Atto Round 1 (Codeforces Round 1041, Div. 1 + Div. 2) ›

CF 2127H - 23 Rises Again

CF 2127H - 23 Rises Again Rating: 3100 Tags: brute force, dfs and similar, dp, flows, graph matchings, graphs, greedy, implementation, probabilities, trees Solve time: 1m 42s Verified: yes Solution Problem Understanding We are given an undirected, connected graph with up to 30 vertices, where each vertex belongs to at most 5 simple cycles. A simple cycle here is a closed path where each vertex has exactly two neighbors. A...

Practice › Codeforces Solutions › Codeforces Round 1042 (Div. 3) ›

CF 2131G - Wafu!

CF 2131G - Wafu! Rating: 2000 Tags: bitmasks, brute force, data structures, dfs and similar, dp, math Solve time: 2m 17s Verified: no Solution Problem Understanding We start with a finite set of distinct positive integers. A single move depends entirely on the current minimum element of the set. That minimum is removed, contributes multiplicatively to an accumulating score, and then triggers a structural change: every integer smaller than it...

Practice › Codeforces Solutions › Codeforces Round 1043 (Div. 3) ›

CF 2132F - Rada and the Chamomile Valley

CF 2132F - Rada and the Chamomile Valley Rating: 2100 Tags: dfs and similar, graphs, shortest paths Solve time: 1m 41s Verified: no Solution Problem Understanding We are asked to analyze a connected undirected graph representing the Chamomile Valley, where nodes are houses and edges are lanes between them. Rada wants to know which lanes are guaranteed to be part of every shortest path from house 1 to house n....

Practice › Codeforces Solutions › Codeforces Round 1044 (Div. 2) ›

CF 2133E - I Yearned For The Mines

CF 2133E - I Yearned For The Mines Rating: 2500 Tags: constructive algorithms, dfs and similar, dp, greedy, trees Solve time: 1m 34s Verified: no Solution Problem Understanding We are working on a tree where an adversary occupies exactly one node, but we never know which one. The adversary is also reactive: after each of our actions, they are allowed to move along one edge or stay in place, except...

Practice › Codeforces Solutions › Codeforces Round 1045 (Div. 2) ›

CF 2134D - Sliding Tree

CF 2134D - Sliding Tree Rating: 2300 Tags: constructive algorithms, dfs and similar, greedy, implementation, trees Solve time: 1m 30s Verified: no Solution Problem Understanding We are given a tree and a very specific local rewiring operation. The operation picks a vertex $b$ with two distinguished neighbors $a$ and $c$. After that, every other neighbor of $b$ is detached from $b$ and reattached to $c$. Intuitively, one neighbor of $b$...

Practice › Codeforces Solutions › Codeforces Round 1046 (Div. 1) ›

CF 2135C - By the Assignment

CF 2135C - By the Assignment Rating: 2000 Tags: binary search, bitmasks, combinatorics, dfs and similar, dsu, graphs, math Solve time: 1m 52s Verified: no Solution Problem Understanding We are given a connected undirected graph where each vertex may have a weight, but some weights are missing and represented by -1 . The goal is to fill in the missing weights such that the graph becomes balanced . A graph...

Practice › Codeforces Solutions › Codeforces Round 1047 (Div. 3) ›

CF 2137G - Cry Me a River

CF 2137G - Cry Me a River Rating: 2200 Tags: dfs and similar, dp, games, graphs Solve time: 1m 29s Verified: no Solution Problem Understanding We are given a directed acyclic graph with n nodes and m edges. Each node starts colored blue, and players Cry and River play a two-player token game. The token starts at a node s . Cry moves first, then River, and they alternate. Cry...

Practice › Codeforces Solutions › Codeforces Round 1048 (Div. 1) ›

CF 2138C2 - Maple and Tree Beauty (Hard Version)

CF 2138C2 - Maple and Tree Beauty (Hard Version) Rating: 2000 Tags: bitmasks, brute force, dfs and similar, dp, fft, trees Solve time: 1m 32s Verified: no Solution Problem Understanding We are given a rooted tree with n vertices. Each vertex must be labeled either 0 or 1 , with exactly k zeros and n - k ones. The "name" of a vertex is the string formed by concatenating the...

Practice › Codeforces Solutions › Codeforces Round 1048 (Div. 1) ›

CF 2138C1 - Maple and Tree Beauty (Easy Version)

CF 2138C1 - Maple and Tree Beauty (Easy Version) Rating: 1800 Tags: brute force, dfs and similar, dp, graphs, trees Solve time: 1m 38s Verified: no Solution Problem Understanding We are given a rooted tree with n vertices, where the root is vertex 1. Each vertex is labeled either 0 or 1, but we do not know the exact labeling. All we know is that exactly k vertices have label...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 13 ›

CF 2141H - Merging Vertices in a Graph

CF 2141H - Merging Vertices in a Graph Rating: 2700 Tags: *special, dfs and similar, dsu, graphs Solve time: 1m 20s Verified: yes Solution Problem Understanding We start with an undirected simple graph on $n$ vertices. The graph evolves through an operation that removes two existing vertices and replaces them with a new vertex whose neighborhood is exactly the intersection of the neighborhoods of the removed vertices. In other words,...

Practice › Codeforces Solutions › Codeforces Round 1051 (Div. 2) ›

CF 2143C - Max Tree

CF 2143C - Max Tree Rating: 1300 Tags: constructive algorithms, dfs and similar, graphs, greedy Solve time: 1m 41s Verified: no Solution Problem Understanding We are given a tree with n vertices and n-1 edges, each edge carrying two non-negative integers x and y . The problem asks us to assign distinct integers from 1 to n to the vertices so that the sum of edge contributions is maximized. Each...

Practice › Codeforces Solutions › Educational Codeforces Round 183 (Rated for Div. 2) ›

CF 2145F - Long Journey

CF 2145F - Long Journey Rating: 2500 Tags: dfs and similar, divide and conquer, dp, graphs, greedy, math, matrices, number theory Solve time: 1m 43s Verified: no Solution Problem Understanding We are given a very long one-dimensional strip of cells, numbered from 0 up to m. A chip starts at cell 0 and wants to reach cell m in as few turns as possible. Each turn, the chip either stays...

Practice › Codeforces Solutions › Educational Codeforces Round 183 (Rated for Div. 2) ›

CF 2145D - Inversion Value of a Permutation

CF 2145D - Inversion Value of a Permutation Rating: 1800 Tags: constructive algorithms, dfs and similar, dp Solve time: 1m 36s Verified: no Solution Problem Understanding We are asked to construct a permutation of length $n$, meaning we must arrange the numbers from $1$ to $n$ exactly once in some order. For any fixed permutation, we can look at its inversions, which are pairs of positions where a larger number...

Practice › Codeforces Solutions › Squarepoint Challenge (Codeforces Round 1055, Div. 1 + Div. 2) ›

CF 2152H1 - Victorious Coloring (Easy Version)

CF 2152H1 - Victorious Coloring (Easy Version) Rating: 2900 Tags: dfs and similar, dp, greedy Solve time: 5m 6s Verified: no Solution Problem Understanding We are given a tree with n vertices, each edge has a positive weight. The task is to assign nonnegative integer weights to the vertices themselves so that when we compute the minimum cost of a “victorious coloring” (coloring vertices red or yellow with at least...

Practice › Codeforces Solutions › Codeforces Round 1060 (Div. 2) ›

CF 2154D - Catshock

CF 2154D - Catshock Rating: 1900 Tags: constructive algorithms, dfs and similar, graphs, trees, two pointers Solve time: 3m 16s Verified: no Solution Problem Understanding The tree represents a world where a cat starts at node 1 and tries to reach node n. You cannot directly control the cat’s path when it moves. Instead, you give a script made of two kinds of commands: one command forces the cat to...

Practice › Codeforces Solutions › Codeforces Round 1056 (Div. 2) ›

CF 2155F - Juan's Colorful Tree

CF 2155F - Juan's Colorful Tree Rating: 2800 Tags: data structures, dfs and similar, dsu, graphs, meet-in-the-middle, trees Solve time: 1m 56s Verified: no Solution Problem Understanding We are given a tree with n nodes, where each node contains a set of colors drawn from a palette of size k . Each node's set may be different, and the total number of color assignments across all nodes is s ....

Practice › Codeforces Solutions › Codeforces Round 1066 (Div. 1 + Div. 2) ›

CF 2157H - Keygen 3

CF 2157H - Keygen 3 Rating: 3200 Tags: brute force, combinatorics, constructive algorithms, dfs and similar, math Solve time: 1m 45s Verified: no Solution Problem Understanding We are asked to construct permutations of size $n$ that satisfy two independent structural constraints, and then output as many distinct valid permutations as exist, capped at 2000. A permutation here can be viewed as a directed graph on $n$ nodes where each index...

Practice › Codeforces Solutions › Codeforces Round 1066 (Div. 1 + Div. 2) ›

CF 2157G - Isaac's Queries

CF 2157G - Isaac's Queries Rating: 2800 Tags: bitmasks, brute force, constructive algorithms, dfs and similar, divide and conquer, dp, greedy, interactive, math, probabilities Solve time: 1m 49s Verified: no Solution Problem Understanding We are dealing with a hidden array of integers, where each integer is in the range [0, 2^30) . We are allowed to ask queries about contiguous subarrays. For a query on the interval [u, v] ,...

Practice › Codeforces Solutions › Codeforces Global Round 30 (Div. 1 + Div. 2) ›

CF 2164F2 - Chain Prefix Rank (Hard Version)

CF 2164F2 - Chain Prefix Rank (Hard Version) Rating: 2900 Tags: binary search, combinatorics, data structures, dfs and similar, dp, graphs, math, trees Solve time: 1m 51s Verified: no Solution Problem Understanding We are given a rooted tree where every vertex has a fixed parent, and thus a fixed ancestor structure. Alongside this tree, each vertex $u$ comes with a target number $a_u$. We are asked to count how many...

Practice › Codeforces Solutions › Codeforces Global Round 30 (Div. 1 + Div. 2) ›

CF 2164F1 - Chain Prefix Rank (Easy Version)

CF 2164F1 - Chain Prefix Rank (Easy Version) Rating: 2600 Tags: combinatorics, dfs and similar, dp, math, trees Solve time: 2m 26s Verified: yes Solution Problem Understanding We are given a rooted tree with $n$ nodes, labeled from $1$ to $n$, with node $1$ as the root. For each node $u$, a number $a_u$ is specified. This number represents the count of ancestors $v$ of $u$ (including $u$ itself if...

Practice › Codeforces Solutions › Codeforces Global Round 30 (Div. 1 + Div. 2) ›

CF 2164E - Journey

CF 2164E - Journey Rating: 2300 Tags: data structures, dfs and similar, dsu, graphs, greedy Solve time: 1m 52s Verified: no Solution Problem Understanding We are given an undirected connected graph with vertices and weighted edges. We start at vertex 1 and must traverse the graph such that every edge is marked at least once, returning to the start. We have two modes of movement: walking along an edge at...

Practice › Codeforces Solutions › Codeforces Round 1062 (Div. 4) ›

CF 2167F - Tree, TREE!!!

CF 2167F - Tree, TREE!!! Rating: 1600 Tags: dfs and similar, dp, math, trees Solve time: 1m 47s Verified: no Solution Problem Understanding We are given an unrooted tree and a parameter $k$. For every possible choice of a root $r$, we conceptually “re-root” the tree at $r$ and then look at all ways of selecting exactly $k$ distinct nodes. For each such selection, we compute their lowest common ancestor...

Practice › Codeforces Solutions › Codeforces Round 1069 (Div. 1) ›

CF 2174E2 - Game of Scientists (Version 2)

CF 2174E2 - Game of Scientists (Version 2) Rating: 3200 Tags: binary search, chinese remainder theorem, dfs and similar, interactive, math Solve time: 3m 37s Verified: no Solution Problem Understanding We are interacting with a hidden integer $x$ that is fixed for each game and always lies in the range $[1, c]$, where $c = 2 \cdot 10^9$. Our goal is to determine this number using at most three queries....

Practice › Codeforces Solutions › Codeforces Round 1070 (Div. 2) ›

CF 2176E - Remove at the lowest cost

CF 2176E - Remove at the lowest cost Rating: 2400 Tags: data structures, dfs and similar, dp, dsu, greedy, implementation, trees Solve time: 2m 15s Verified: no Solution Problem Understanding We are given an array of n elements. Each element has a value a_i and a removal cost c_i . The goal is to remove all elements except one, using a series of adjacent removals, paying the minimum total cost....

Practice › Codeforces Solutions › Educational Codeforces Round 186 (Rated for Div. 2) ›

CF 2182G - Short Garland

CF 2182G - Short Garland Rating: 2800 Tags: combinatorics, data structures, dfs and similar, dp, trees Solve time: 1m 47s Verified: no Solution Problem Understanding We are given a rooted tree with vertex 1 fixed as the root. A sequence of n “placements” must be assigned, one for each vertex of the tree, but the twist is that the placement order is not arbitrary. The first placement is forced onto...

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183F - Jumping Man

CF 2183F - Jumping Man Rating: 2500 Tags: brute force, combinatorics, dfs and similar, dp, trees Solve time: 2m 24s Verified: no Solution Problem Understanding We are given a rooted tree with each node labeled by a lowercase letter. For each node $i$, we are asked to analyze all strings that can be formed by starting at any node in the subtree of $i$ and repeatedly jumping to a proper...

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183D2 - Tree Coloring (Hard Version)

CF 2183D2 - Tree Coloring (Hard Version) Rating: 2100 Tags: combinatorics, constructive algorithms, data structures, dfs and similar, greedy, implementation, trees Solve time: 1m 58s Verified: no Solution Problem Understanding We are given a rooted tree, where all nodes are initially white, and we need to color all nodes black in the minimum number of operations. Each operation allows selecting a set of white nodes with two constraints: no two...

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183D1 - Tree Coloring (Easy Version)

CF 2183D1 - Tree Coloring (Easy Version) Rating: 1500 Tags: constructive algorithms, dfs and similar, greedy, trees Solve time: 2m 31s Verified: no Solution Problem Understanding We are given a rooted tree with n vertices, where the root is vertex 1 , and initially all vertices are white. The distance d_i of a vertex i is the number of edges on the path from the root to i . We...

Practice › Codeforces Solutions › Codeforces Round 1072 (Div. 3) ›

CF 2184F - Cherry Tree

CF 2184F - Cherry Tree Rating: 1900 Tags: dfs and similar, dp, graphs, trees Solve time: 3m 44s Verified: yes Solution Problem Understanding We have a rooted tree whose leaves each contain exactly one cherry. A shake performed at vertex v makes the cherries fall from every leaf inside the subtree of v . Once a cherry has fallen, it must never be affected by another shake. If any leaf...

Practice › Codeforces Solutions › Codeforces Round 1072 (Div. 3) ›

CF 2184C - Huge Pile

CF 2184C - Huge Pile Rating: 1100 Tags: binary search, dfs and similar, dp, graphs, math Solve time: 1m 43s Verified: yes Solution Problem Understanding Andrei starts with a single pile containing $n$ apples. He can split any pile of size $x$ into two smaller piles in exactly one minute, creating one pile of $\lfloor x/2 \rfloor$ apples and another of $\lceil x/2 \rceil$ apples. His goal is to obtain...

Practice › Codeforces Solutions › Codeforces Round 1077 (Div. 1) ›

CF 2187C - Jerry and Tom

CF 2187C - Jerry and Tom Rating: 2300 Tags: data structures, dfs and similar, dsu, games, graphs, greedy, trees Solve time: 2m 26s Verified: no Solution Problem Understanding We are asked to analyze a two-player game on a directed graph with $n$ vertices. The graph is almost a chain: for every vertex $u$ from 1 to $n-1$, there is an edge $u \to u+1$. On top of this, there are...

Practice › Codeforces Solutions › Codeforces Round 1075 (Div. 2) ›

CF 2189F - Zhora the Vacuum Cleaner

CF 2189F - Zhora the Vacuum Cleaner Rating: 2800 Tags: data structures, dfs and similar, dp, greedy, implementation, sortings, trees Solve time: 3m 5s Verified: no Solution Problem Understanding We have a tree. Vertex i initially contains a_i nuts. There are two kinds of electricity costs. The first cost comes from a special redistribution operation. We choose a vertex v . Then every other vertex is processed from larger distance...

Practice › Codeforces Solutions › Codeforces Round 1081 (Div. 2) ›

CF 2192E - Swap to Rearrange

CF 2192E - Swap to Rearrange Rating: 2100 Tags: constructive algorithms, dfs and similar, graph matchings, graphs, greedy, strings Solve time: 2m 32s Verified: no Solution Problem Understanding Each position i contains a pair of values (a_i, b_i) . For that position we have exactly two choices. If we do nothing, the value a_i stays in array a and b_i stays in array b . If we swap that position,...

Practice › Codeforces Solutions › Codeforces Round 1076 (Div. 3) ›

CF 2193H - Remove the Grail Tree

CF 2193H - Remove the Grail Tree Rating: 2400 Tags: dfs and similar, dp, graphs, greedy, implementation, trees Solve time: 2m 9s Verified: no Solution Problem Understanding We are given a tree, which is a connected acyclic graph with $n$ vertices, and each vertex has an associated integer value. The operation we can perform repeatedly is to remove a vertex if the sum of the values of its remaining neighbors...

Practice › Codeforces Solutions › Codeforces Round 1076 (Div. 3) ›

CF 2193G - Paths in a Tree

CF 2193G - Paths in a Tree Rating: 2100 Tags: dfs and similar, interactive, sortings, trees Solve time: 3m 5s Verified: no Solution Problem Understanding We are given a tree, which is an undirected, connected, acyclic graph of $n$ vertices. Two hidden vertices, $x$ and $y$, define a unique path because trees have exactly one simple path between any pair of vertices. We do not know the identities of $x$...

Practice › Codeforces Solutions › Codeforces Round 1078 (Div. 2) ›

CF 2194F2 - Again Trees... (hard version)

CF 2194F2 - Again Trees... (hard version) Rating: 3000 Tags: bitmasks, data structures, dfs and similar, dp, fft, trees Solve time: 1m 47s Verified: no Solution Problem Understanding We are asked to count certain ways to cut a tree into connected components with a specific property. The tree has n vertices, each with a value a_v . We are also given a small set of numbers b_1, ..., b_k ....

Practice › Codeforces Solutions › Codeforces Round 1078 (Div. 2) ›

CF 2194F1 - Again Trees... (Easy Version)

CF 2194F1 - Again Trees... (Easy Version) Rating: 2300 Tags: bitmasks, dfs and similar, dp, trees Solve time: 1m 35s Verified: yes Solution Problem Understanding We are given a tree with n vertices, where each vertex has a non-negative integer a_v written on it. We are also given a set of k distinct non-negative integers b_1, ..., b_k . The task is to count the number of ways to remove...

Practice › Codeforces Solutions › Codeforces Round 1080 (Div. 3) ›

CF 2195E - Idiot First Search

CF 2195E - Idiot First Search Rating: 1500 Tags: dfs and similar, dp, trees Solve time: 2m 4s Verified: no Solution Problem Understanding We are given a rooted binary tree where vertex 0 is the root and every other vertex is either a leaf or has exactly two children, left and right. The vertices are numbered, and the structure is fully specified by child pointers. A token starts at some...

Practice › Codeforces Solutions › Codeforces Round 1079 (Div. 1) ›

CF 2196C2 - Interactive Graph (Hard Version)

CF 2196C2 - Interactive Graph (Hard Version) Rating: 2000 Tags: combinatorics, dfs and similar, dp, graphs, interactive Solve time: 2m 10s Verified: no Solution Problem Understanding We are asked to reconstruct a hidden directed acyclic graph (DAG) by interacting with a system that enumerates all paths in lexicographic order. Each query allows us to ask for the $k$-th path. The paths are sequences of vertex indices such that consecutive vertices...

Practice › Codeforces Solutions › Codeforces Round 1079 (Div. 1) ›

CF 2196C1 - Interactive Graph (Simple Version)

CF 2196C1 - Interactive Graph (Simple Version) Rating: 1800 Tags: binary search, combinatorics, dfs and similar, dp, graphs, interactive Solve time: 1m 53s Verified: no Solution Problem Understanding We are given a directed acyclic graph with up to 15 vertices. The edges are unknown, but we are allowed to probe the graph through an oracle. Each query asks for the k-th path in the lexicographically sorted list of all valid...

Practice › Codeforces Solutions › Educational Codeforces Round 188 (Rated for Div. 2) ›

CF 2204D - Alternating Path

CF 2204D - Alternating Path Rating: 1400 Tags: constructive algorithms, dfs and similar, graph matchings, graphs Solve time: 1m 50s Verified: no Solution Problem Understanding We are given an undirected graph and asked to assign a direction to each edge such that some vertices become "beautiful". A vertex is beautiful if, starting from it, every path in the original graph alternates directions along the edges: the first edge must go...

Practice › Codeforces Solutions › 2026 ICPC Asia Pacific Championship - Online Mirror (Unrated, Online Mirror, ICPC Rules, Teams Preferred) ›

CF 2206C - Upside Down Dijkstra

CF 2206C - Upside Down Dijkstra Rating: 2200 Tags: dfs and similar Solve time: 2m 25s Verified: no Solution Problem Understanding We are given a connected undirected graph with $n$ vertices and $m$ edges, where each edge connects two vertices but its weight is unknown. Your sibling ran a variant of Dijkstra's algorithm starting from vertex $1$, but with a crucial mistake: instead of always popping the minimum distance from...

Practice › Codeforces Solutions › Codeforces Round 1085 (Div. 1 + Div. 2) ›

CF 2207G - Toothless

CF 2207G - Toothless Rating: 3300 Tags: constructive algorithms, dfs and similar, dsu Solve time: 2m 4s Verified: no Solution Problem Understanding We are given an n × m grid representing sand, initially all white. Some cells are marked as needy ( # ) and must be painted black. Other cells are either special ( x ) or normal ( . ), and each non-needy cell has a value: special...

Practice › Codeforces Solutions › Codeforces Round 1085 (Div. 1 + Div. 2) ›

CF 2207D - Boxed Like a Fish

CF 2207D - Boxed Like a Fish Rating: 2200 Tags: dfs and similar, dp, games, shortest paths, trees Solve time: 1m 46s Verified: no Solution Problem Understanding We are given a tree where a token starts at a fixed non-leaf vertex. The goal is to determine whether this token can be guaranteed to reach any leaf vertex if two players act in turns. One player controls the token. Each turn,...

Practice › Codeforces Solutions › Codeforces Round 1086 (Div. 2) ›

CF 2208D1 - Tree Orientation (Easy Version)

CF 2208D1 - Tree Orientation (Easy Version) Rating: 1800 Tags: constructive algorithms, dfs and similar, dsu, graphs, greedy, matrices, trees Solve time: 3m 24s Verified: no Solution Problem Understanding We are given a binary reachability matrix for a directed graph on $n$ nodes. The matrix tells us, for every ordered pair $(i, j)$, whether node $i$ can reach node $j$ through directed edges. The underlying graph that produced this matrix...

Practice › Codeforces Solutions › Codeforces Round 1086 (Div. 2) ›

CF 2208D2 - Tree Orientation (Hard Version)

CF 2208D2 - Tree Orientation (Hard Version) Rating: 2200 Tags: dfs and similar, dsu, graphs, greedy, sortings, trees Solve time: 1m 57s Verified: no Solution Problem Understanding We are given a directed reachability matrix of a tree after all its edges have been assigned directions, and we need to reconstruct a tree and its edge directions that produce exactly the same reachability information. Each row of the matrix corresponds to...

Practice › Codeforces Solutions ›

2026 ICPC Asia Pacific Championship - Online Mirror (Unrated, Online Mirror, ICPC Rules, Teams Preferred)

2026 ICPC Asia Pacific Championship - Online Mirror (Unrated, Online Mirror, ICPC Rules, Teams Preferred) ICPC/IOI | 13 problems | 3/13 verified | Difficulty 1300-3500 | 28m 52s # Problem Rating Tags Accepted Time ✓ A Compare Suffixes 3500 interactive 84 1m 54s B Subtree Removal Game 2500 binary-search, games, trees 347 2m 20s ✓ C Upside Down Dijkstra 2200 dfs-and-similar 625 2m 25s D Christmas Tree Un-decoration 2600 data-structures,...

Practice › Codeforces Solutions ›

Codeforces Round 1077 (Div. 1)

Codeforces Round 1077 (Div. 1) Div. 1 | 8 problems | 0/8 verified | Difficulty 1300-3500 | 15m 1s # Problem Rating Tags Accepted Time ✓ A Restricted Sorting 1300 greedy, sortings 15,850 3m 14s B Shortest Statement Ever 5,276 C Jerry and Tom 2300 data-structures, dfs-and-similar, dsu 1,369 2m 26s D Cool Problem 634 E Doors and Keys 3500 brute-force, data-structures, dp 325 2m 11s F1 Al Fine (Maximizing...

Practice › Codeforces Solutions ›

Codeforces Round 1072 (Div. 3)

Codeforces Round 1072 (Div. 3) Div. 3 | 7 problems | 3/7 verified | Difficulty 800-1900 | 16m 4s # Problem Rating Tags Accepted Time ✓ A Social Experiment 800 math 38,048 1m 48s ✓ B Hourglass 1100 math 24,079 2m 15s C Huge Pile 1100 binary-search, dfs-and-similar, dp 21,840 1m 43s ✓ D Unfair Game 1600 combinatorics, dp, math 9,486 2m 38s E Exquisite Array 1800 combinatorics, data-structures, dsu...

Practice › Codeforces Solutions ›

Codeforces Round 277 (Div. 2)

Codeforces Round 277 (Div. 2) Div. 2 | 5 problems | 5/5 verified | Difficulty 800-2200 | 9m 11s # Problem Rating Tags Accepted Time ✓ A Calculating Function 800 implementation, math 154,077 1m 34s ✓ B OR in Matrix 1300 greedy, hashing, implementation 19,167 1m 32s ✓ C Palindrome Transformation 1700 brute-force, greedy, implementation 12,370 1m 44s ✓ D Valid Sets 2100 dfs-and-similar, dp, math 4,380 1m 58s ✓...

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Codeforces Round 282 (Div. 1)

Codeforces Round 282 (Div. 1) Div. 1 | 5 problems | 4/5 verified | Difficulty 1500-3200 | 7m 13s # Problem Rating Tags Accepted Time ✓ A Treasure 1500 greedy 6,548 1m 33s ✓ B Obsessive String 2000 dp, strings 3,111 1m 52s ✓ C Helping People 2600 dp, probabilities 958 42s ✓ D Birthday 2700 data-structures, dfs-and-similar, dp 669 1m 47s E Sharti 3200 data-structures, games 374 1m 19s...

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Codeforces Round 277.5 (Div. 2)

Codeforces Round 277.5 (Div. 2) Div. 2 | 6 problems | 4/6 verified | Difficulty 1200-2300 | 12m 13s # Problem Rating Tags Accepted Time ✓ A SwapSort 1200 greedy, implementation, sortings 10,585 2m 34s B BerSU Ball 1200 dfs-and-similar, dp, graph-matchings 56,718 2m 3s ✓ C Given Length and Sum of Digits... 1400 dp, greedy, implementation 51,664 1m 25s ✓ D Unbearable Controversy of Being 1700 brute-force, combinatorics, dfs-and-similar...

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Educational Codeforces Round 163 (Rated for Div. 2)

Educational Codeforces Round 163 (Rated for Div. 2) Div. 2 | 7 problems | 5/7 verified | Difficulty 800-3100 | 10m 51s # Problem Rating Tags Accepted Time ✓ A Special Characters 800 brute-force, constructive-algorithms 30,987 1m 15s ✓ B Array Fix 1100 brute-force, dp, greedy 26,268 1m 29s ✓ C Arrow Path 1300 brute-force, constructive-algorithms, dfs-and-similar 21,090 56s ✓ D Tandem Repeats? 1700 brute-force, strings, two-pointers 12,295 1m 24s...

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Codeforces Round 237 (Div. 2)

Codeforces Round 237 (Div. 2) Div. 2 | 5 problems | 3/5 verified | Difficulty 1000-2200 | 24m 8s # Problem Rating Tags Accepted Time ✓ A Valera and X 1000 implementation 26,203 4m 41s ✓ B Marathon 1500 implementation, math 3,049 4m 20s ✓ C Restore Graph 1800 dfs-and-similar, graphs, sortings 5,787 6m 13s D Minesweeper 1D 1900 dp, implementation 2,465 4m 20s ✓ E Maze 1D 2200 binary-search,...

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Codeforces Round 238 (Div. 2)

Codeforces Round 238 (Div. 2) Div. 2 | 5 problems | 3/5 verified | Difficulty 900-2300 | 22m 48s # Problem Rating Tags Accepted Time ✓ A Gravity Flip 900 greedy, implementation, sortings 126,418 4m 16s ✓ B Domino Effect 1100 6,107 4m 21s ✓ C Unusual Product 1600 implementation, math 4,931 4m 31s ✓ D Toy Sum 1700 greedy, implementation, math 3,287 4m 56s E Graph Cutting 2300 dfs-and-similar,...

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Coder-Strike 2014 - Round 1

Coder-Strike 2014 - Round 1 Special | 5 problems | 4/5 verified | Difficulty 900-2000 | 15m 58s # Problem Rating Tags Accepted Time ✓ A Poster 900 greedy, implementation 4,965 1m 37s ✓ B Network Configuration 900 greedy, sortings 6,356 4m 25s ✓ C Pattern 1200 implementation, strings 4,220 4m 23s ✓ D Giving Awards 2000 dfs-and-similar 2,437 1m 55s ✓ E E-mail Addresses 1900 implementation 938 3m 38s

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Testing Round 10

Testing Round 10 Special | 4 problems | 2/4 verified | Difficulty 800-2200 | 4m 59s # Problem Rating Tags Accepted Time ✓ A Forgotten Episode 800 implementation 8,918 1m 1s ✓ B Balancer 1600 greedy, implementation 2,325 1m 3s ✓ C One-Based Arithmetic 1800 brute-force, dfs-and-similar, divide-and-conquer 1,139 1m 30s D Berland Federalization 2200 dp, trees 942 1m 25s

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CF 2222G - Statistics on Tree

CF 2222G - Statistics on Tree Rating: - Tags: binary search, brute force, dfs and similar, divide and conquer, graphs, trees Solve time: 1m 43s Verified: no Solution Problem Understanding We are working with a tree where each pair of vertices defines a path. For any pair of nodes $(u, v)$, we look at the unique simple path connecting them and then imagine removing all edges on that path from...

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CF 2219C - Coloring a Red Black Tree

CF 2219C - Coloring a Red Black Tree Rating: - Tags: dfs and similar, dp, greedy, math, probabilities, trees Solve time: 3m 53s Verified: no Solution Problem Understanding We are given a tree with n nodes, where each node is initially colored either red or black according to a binary string. Red nodes are marked 1 and black nodes 0 . The task is to turn all nodes red by...

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CF 2217H - Closer

CF 2217H - Closer Rating: 2800 Tags: dfs and similar, dp, trees Solve time: 2m 1s Verified: no Solution Problem Understanding We have a tree with $2n$ vertices, each hosting a single person. Every person carries a badge corresponding to one of $n$ deals, and each deal appears exactly twice among the people. If the two people holding the same deal badge are on adjacent vertices, the deal is immediately...

Practice › Codeforces Solutions › Codeforces Round 943 (Div. 3) ›

CF 1968D - Permutation Game

CF 1968D - Permutation Game Rating: 1300 Tags: brute force, dfs and similar, games, graphs, greedy, math Solve time: 1m 22s Verified: yes Solution Problem Understanding We are given a directed structure formed by a permutation. From each index $x$, there is exactly one outgoing edge to $p_x$, so the entire system decomposes into disjoint directed cycles, possibly with trees feeding into them, but because $p$ is a permutation, every...

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CF 1957F2 - Frequency Mismatch (Hard Version)

CF 1957F2 - Frequency Mismatch (Hard Version) Rating: 2700 Tags: binary search, data structures, dfs and similar, hashing, probabilities, trees Solve time: 1m 53s Verified: no Solution Problem Understanding We are given a tree with $n$ nodes, each node labeled with an integer value. The tree is unrooted, but conceptually we can root it anywhere for processing. For each query, we are asked to compare the multiset of values along...

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CF 1952G - Mathematician Takeover

CF 1952G - Mathematician Takeover Rating: - Tags: *special, binary search, dfs and similar, math Solve time: 1m 42s Verified: no Solution Problem Understanding We are given a single real number $x$ between 1 and 100, precise to three decimal places. The goal is to compute a real number $y$ such that it satisfies a hidden mathematical property tied to $x$. The problem is unusual in that the official statement...

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CF 1946F - Nobody is needed

CF 1946F - Nobody is needed Rating: 2500 Tags: 2-sat, data structures, dfs and similar, dp Solve time: 1m 38s Verified: no Solution Problem Understanding We are given a permutation of integers from 1 to $n$ and a series of queries. Each query asks how many sequences of indices in a specified range $[l, r]$ can be formed such that the sequence is strictly increasing and each element divides the...

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CF 494D - Birthday

CF 494D - Birthday Rating: 2700 Tags: data structures, dfs and similar, dp, trees Solve time: 1m 47s Verified: no Solution Problem Understanding We are given a rooted tree with n vertices, where vertex 1 is the root. Each edge has a positive weight, and the distance between any two vertices is the sum of the weights along the unique path connecting them. For each vertex v , we define...

Practice › Codeforces Solutions › Codeforces Round 279 (Div. 2) ›

CF 490F - Treeland Tour

CF 490F - Treeland Tour Rating: 2200 Tags: data structures, dfs and similar, dp, trees Solve time: 1m 28s Verified: yes Solution Problem Understanding We are given a tree of cities, where each city has a population. The roads connect cities such that there is exactly one simple path between any two cities. The band wants to perform in a sequence of cities along some path, with the populations strictly...

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CF 490D - Chocolate

CF 490D - Chocolate Rating: 1900 Tags: brute force, dfs and similar, math, meet-in-the-middle, number theory Solve time: 1m 25s Verified: yes Solution Problem Understanding Each chocolate bar is a rectangle made of unit squares, so its “value” is just its area. We start with two rectangles and we are allowed to modify them minute by minute. In one minute we pick exactly one bar and reduce its area by...

Practice › Codeforces Solutions › Codeforces Round 277.5 (Div. 2) ›

CF 489D - Unbearable Controversy of Being

CF 489D - Unbearable Controversy of Being Rating: 1700 Tags: brute force, combinatorics, dfs and similar, graphs Solve time: 1m 53s Verified: yes Solution Problem Understanding We are given a directed graph representing intersections and one-way roads. A "damn rhombus" consists of four distinct vertices $a, b, c, d$ such that there are directed edges $$a \rightarrow b,\quad b \rightarrow c,\quad a \rightarrow d,\quad d \rightarrow c$$ In other words,...

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CF 489B - BerSU Ball

CF 489B - BerSU Ball Rating: 1200 Tags: dfs and similar, dp, graph matchings, greedy, sortings, two pointers Solve time: 2m 3s Verified: yes Solution Problem Understanding We have two groups of dancers. Each boy has a skill level, and each girl has a skill level. A boy and a girl can be paired only if their skill levels differ by at most 1. Every dancer can belong to at...

Practice › Codeforces Solutions › Codeforces Round 278 (Div. 1) ›

CF 487E - Tourists

CF 487E - Tourists Rating: 3200 Tags: data structures, dfs and similar, graphs, trees Solve time: 1m 43s Verified: no Solution Problem Understanding We are asked to handle queries on a connected undirected graph representing cities in Cyberland. Each city has a souvenir price, and roads connect pairs of cities. There are two query types: updating the souvenir price in a city, and asking the minimum souvenir price along any...

Practice › Codeforces Solutions › Codeforces Round 277 (Div. 2) ›

CF 486D - Valid Sets

CF 486D - Valid Sets Rating: 2100 Tags: dfs and similar, dp, math, trees Solve time: 1m 58s Verified: yes Solution Problem Understanding We are given a tree where every vertex has an integer value. A set of vertices is considered valid if it is non-empty, forms a connected subgraph of the tree, and the difference between the largest and smallest value inside the set does not exceed d ....

Practice › Codeforces Solutions › Codeforces Round 266 (Div. 2) ›

CF 466E - Information Graph

CF 466E - Information Graph Rating: 2100 Tags: dfs and similar, dsu, graphs, trees Solve time: 2m 46s Verified: yes Solution Problem Understanding We have a company hierarchy that is built gradually over time. Initially nobody has a boss. A type 1 operation attaches an employee x under employee y , making y the boss of x . The input guarantees that x currently has no boss, and cycles never...

Practice › Codeforces Solutions › Codeforces Round 256 (Div. 2) ›

CF 448E - Divisors

CF 448E - Divisors Rating: 2200 Tags: brute force, dfs and similar, implementation, number theory Solve time: 1m 45s Verified: yes Solution Problem Understanding We are given a number X and an integer k , and we want to construct a sequence by repeatedly expanding each number into its divisors in increasing order. Formally, we define _X_0 as a sequence containing just X . For each i > 0, X**i...

Practice › Codeforces Solutions › Codeforces Round 254 (Div. 2) ›

CF 445B - DZY Loves Chemistry

CF 445B - DZY Loves Chemistry Rating: 1400 Tags: dfs and similar, dsu, greedy Solve time: 1m 49s Verified: yes Solution Problem Understanding The chemicals and reactions form an undirected graph. Each vertex represents a chemical, and an edge between two vertices means those two chemicals react. We start with danger equal to 1. Chemicals are poured one at a time in any order. Whenever the newly added chemical has...

Practice › Codeforces Solutions › Codeforces Round 252 (Div. 2) ›

CF 441C - Valera and Tubes

CF 441C - Valera and Tubes Rating: 1500 Tags: constructive algorithms, dfs and similar, implementation Solve time: 1m 35s Verified: no Solution Problem Understanding We are given an $n \times m$ grid where every cell must be partitioned into exactly $k$ simple paths. Each path, called a tube, must contain at least two cells and must move only through edge-adjacent cells, never revisiting a cell. In other words, each tube...

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CF 440C - One-Based Arithmetic

CF 440C - One-Based Arithmetic Rating: 1800 Tags: brute force, dfs and similar, divide and conquer Solve time: 1m 30s Verified: no Solution Problem Understanding We are asked to represent a given positive integer $n$ as a sum of numbers, where each number consists entirely of the digit 1 repeated one or more times. For instance, 121 could be represented as 111 + 10, or as 111 + 11 -...

Practice › Codeforces Solutions › Codeforces Round 238 (Div. 2) ›

CF 405E - Graph Cutting

CF 405E - Graph Cutting Rating: 2300 Tags: dfs and similar, graphs Solve time: 4m 44s Verified: no Solution Problem Understanding We are given a connected undirected graph, and we are asked to completely decompose its edges into length-2 paths. Each output piece must look like a chain of three vertices $x - y - z$, meaning we take two edges that share the middle vertex $y$, and every edge...

Practice › Codeforces Solutions › Codeforces Round 237 (Div. 2) ›

CF 404C - Restore Graph

CF 404C - Restore Graph Rating: 1800 Tags: dfs and similar, graphs, sortings Solve time: 6m 13s Verified: no Solution Problem Understanding We are asked to reconstruct an undirected connected graph from a list of shortest distances from one vertex, under the constraint that each vertex can have at most k edges. The input gives the number of vertices n , the maximum degree k , and an array d...

Practice › Codeforces Solutions › Codeforces Round 203 (Div. 2) ›

CF 350E - Wrong Floyd

CF 350E - Wrong Floyd Rating: 2200 Tags: brute force, constructive algorithms, dfs and similar, graphs Solve time: 1m 37s Verified: yes Solution Problem Understanding We are given an undirected, simple, connected graph with $n$ vertices and $m$ edges. In addition, a subset of vertices $a_1, a_2, \dots, a_k$ is designated as “special”. Someone runs a modified Floyd-style procedure: they first build correct shortest-path distances for all pairs using the...

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Codeforces Round 202 (Div. 1)

Codeforces Round 202 (Div. 1) Div. 1 | 5 problems | 2/5 verified | Difficulty 1600-2800 | 8m 22s # Problem Rating Tags Accepted Time ✓ A Mafia 1600 binary-search, math, sortings 14,681 2m 11s B Apple Tree 2100 dfs-and-similar, number-theory, trees 2,283 1m 30s C Subset Sums 2500 brute-force, data-structures 2,741 1m 4s ✓ D Turtles 2500 dp, matrices 2,217 2m 5s E Pilgrims 2800 dfs-and-similar, dp, trees 512...

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Friday the 13th, Programmers Day

Friday the 13th, Programmers Day Special | 7 problems | 6/7 verified | Difficulty 1500-2700 | 13m 16s # Problem Rating Tags Accepted Time ✓ A Expecting Trouble 1500 *special, probabilities 532 1m 36s ✓ B Triskaidekaphobia 2100 *special 129 1m 47s ✓ C Counting Fridays 2000 *special 130 1m 43s ✓ D Chain Letter 2200 *special, dfs-and-similar, graphs 83 1m 27s ✓ E Black Cat Rush 2700 *special 55...

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Codeforces Round 199 (Div. 2)

Codeforces Round 199 (Div. 2) Div. 2 | 5 problems | 4/5 verified | Difficulty 1200-2400 | 8m 19s # Problem Rating Tags Accepted Time ✓ A Xenia and Divisors 1200 greedy, implementation 13,870 1m 36s ✓ B Xenia and Spies 1500 brute-force, greedy, implementation 4,207 1m 32s ✓ C Cupboard and Balloons 1900 geometry 1,995 1m 38s ✓ D Xenia and Dominoes 2100 bitmasks, dfs-and-similar, dp 567 2m 11s...

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ABBYY Cup 3.0 - Finals (online version)

ABBYY Cup 3.0 - Finals (online version) Special | 12 problems | 8/12 verified | Difficulty 1100-3100 | 19m 20s # Problem Rating Tags Accepted Time ✓ A1 Oh Sweet Beaverette 1400 brute-force, implementation 1,528 1m 6s ✓ A2 Oh Sweet Beaverette 1500 data-structures, sortings 1,546 1m 27s ✓ B1 Shave Beaver! 1700 implementation 808 1m 21s ✓ B2 Shave Beaver! 1900 data-structures 831 1m 26s ✓ C1 The Great...

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Codeforces Round 197 (Div. 2)

Codeforces Round 197 (Div. 2) Div. 2 | 5 problems | 4/5 verified | Difficulty 800-2700 | 9m 23s # Problem Rating Tags Accepted Time ✓ A Helpful Maths 800 greedy, implementation, sortings 275,171 1m 24s ✓ B Xenia and Ringroad 1000 implementation 81,340 1m 55s C Xenia and Weights 1700 constructive-algorithms, dfs-and-similar, dp 8,761 2m 14s ✓ D Xenia and Bit Operations 1700 data-structures, trees 32,536 2m 15s ✓...

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Codeforces Round 188 (Div. 1)

Codeforces Round 188 (Div. 1) Div. 1 | 5 problems | 4/5 verified | Difficulty 1600-3100 | 5m 50s # Problem Rating Tags Accepted Time ✓ A Perfect Pair 1600 brute-force 4,938 1m 1s ✓ B Ants 2000 brute-force, implementation 1,659 1m 21s ✓ C Balance 2500 constructive-algorithms, dfs-and-similar, graphs 550 1m 26s D Game with Powers 2300 dp, games 1,256 1m 1s ✓ E Princess and Her Shadow 3100...

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ABBYY Cup 3.0

ABBYY Cup 3.0 Special | 18 problems | 12/18 verified | Difficulty 1100-2400 | 31m 4s # Problem Rating Tags Accepted Time ✓ A1 Special Task 1100 greedy 2,888 1m 18s ✓ A2 Special Task 1400 math 2,295 2m 20s ✓ B1 EKG 1500 brute-force, dfs-and-similar 1,498 1m 33s ✓ B2 EKG 1600 dfs-and-similar, dp 1,780 1m 3s ✓ C1 Tidying Up 2200 flows 592 2m 24s C2 Tidying Up...

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Codeforces Round 187 (Div. 1)

Codeforces Round 187 (Div. 1) Div. 1 | 5 problems | 4/5 verified | Difficulty 1600-2900 | 10m 14s # Problem Rating Tags Accepted Time ✓ A Sereja and Contest 1600 implementation 2,172 2m 24s ✓ B Sereja and Periods 2000 binary-search, dfs-and-similar, strings 1,619 1m 5s ✓ C Sereja and Subsequences 2000 data-structures, dp 2,003 2m 39s ✓ D Sereja and Straight Lines 2500 binary-search, data-structures, geometry 577 1m...

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Codeforces Round 189 (Div. 2)

Codeforces Round 189 (Div. 2) Div. 2 | 2 problems | 2/2 verified | Difficulty 900-1500 | 2m 19s # Problem Rating Tags Accepted Time ✓ A Magic Numbers 900 brute-force, greedy 45,409 1m 6s ✓ B Ping-Pong (Easy Version) 1500 dfs-and-similar, graphs 7,780 1m 13s ✓

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Codeforces Round 192 (Div. 1)

Codeforces Round 192 (Div. 1) Div. 1 | 5 problems | 3/5 verified | Difficulty 1500-2500 | 10m 40s # Problem Rating Tags Accepted Time ✓ A Purification 1500 constructive-algorithms, greedy 4,805 1m 55s ✓ B Biridian Forest 1500 dfs-and-similar, shortest-paths 7,493 1m 46s ✓ C Graph Reconstruction 2400 constructive-algorithms 1,010 5m 49s D The Evil Temple and the Moving Rocks 2500 constructive-algorithms 436 1m 10s ✓ E Evil 183

Practice › Codeforces Solutions › Codeforces Round 202 (Div. 1) ›

CF 348B - Apple Tree

CF 348B - Apple Tree Rating: 2100 Tags: dfs and similar, number theory, trees Solve time: 1m 30s Verified: no Solution Problem Understanding We are given a rooted tree where only the leaves initially contain apples, while internal nodes are empty. Each leaf contributes a fixed number of apples, and the “weight” of any subtree is defined as the total number of apples in all leaves inside that subtree. A...

Practice › Codeforces Solutions › Codeforces Round 202 (Div. 1) ›

CF 348E - Pilgrims

CF 348E - Pilgrims Rating: 2800 Tags: dfs and similar, dp, trees Solve time: 1m 32s Verified: yes Solution Problem Understanding We are given a weighted tree with n towns. Some of these towns contain monasteries, and each monastery hosts exactly one pilgrim. The structure of the country guarantees that every town is reachable from every other, and distances are determined by the sum of edge weights along the unique...

Practice › Codeforces Solutions › Friday the 13th, Programmers Day ›

CF 345D - Chain Letter

CF 345D - Chain Letter Rating: 2200 Tags: *special, dfs and similar, graphs Solve time: 1m 27s Verified: yes Solution Problem Understanding We are given a network of people, where every pair of people either knows each other in both directions or does not know each other at all. This relationship is encoded as an adjacency matrix of size $n \times n$, where a 1 means two people will forward...

Practice › Codeforces Solutions › Codeforces Round 200 (Div. 1) ›

CF 343E - Pumping Stations

CF 343E - Pumping Stations Rating: 2900 Tags: brute force, dfs and similar, divide and conquer, flows, graphs, greedy, trees Solve time: 2m 18s Verified: no Solution Problem Understanding We are asked to maximize the total amount of water Mike can pump across a network of stations in a sequence of days. Each station is a node in an undirected graph, and pipes between stations are edges with capacities. On...

Practice › Codeforces Solutions › Codeforces Round 200 (Div. 1) ›

CF 343D - Water Tree

CF 343D - Water Tree Rating: 2100 Tags: data structures, dfs and similar, graphs, trees Solve time: 1m 36s Verified: yes Solution Problem Understanding We are given a rooted tree where every node behaves like a reservoir that can either contain water or be empty. The root is fixed at node 1, and all edges are directed conceptually away from it. The structure of the tree matters because water operations...

Practice › Codeforces Solutions › Codeforces Round 199 (Div. 2) ›

CF 342D - Xenia and Dominoes

CF 342D - Xenia and Dominoes Rating: 2100 Tags: bitmasks, dfs and similar, dp Solve time: 2m 11s Verified: no Solution Problem Understanding We are given a 3×n grid representing a puzzle board. Each cell can be forbidden, free, or marked with a special circle. Dominoes, which are 1×2 or 2×1 tiles, must be placed to cover exactly two non-forbidden cells. The goal is to place dominoes so that all...

Practice › Codeforces Solutions › Codeforces Round 197 (Div. 2) ›

CF 339E - Three Swaps

CF 339E - Three Swaps Rating: 2700 Tags: constructive algorithms, dfs and similar, greedy Solve time: 1m 35s Verified: yes Solution Problem Understanding We are given a row of n horses, initially numbered from 1 to n from left to right. Xenia performed at most three operations on the row. Each operation consists of reversing the segment between positions l and r , effectively swapping the outer elements inwards until...

Practice › Codeforces Solutions › Codeforces Round 197 (Div. 2) ›

CF 339C - Xenia and Weights

CF 339C - Xenia and Weights Rating: 1700 Tags: constructive algorithms, dfs and similar, dp, graphs, greedy, shortest paths Solve time: 2m 14s Verified: yes Solution Problem Understanding Xenia has access to some subset of weights from 1 through 10 kilograms. For every weight type marked as available, she may use that weight any number of times. She places weights one at a time onto a balance scale. The first...

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CF 316F1 - Suns and Rays

CF 316F1 - Suns and Rays Rating: 2200 Tags: dfs and similar, implementation Solve time: 2m 14s Verified: no Solution Problem Understanding The problem presents an image encoded as a 2D grid of integers where 0 represents the background and 1 represents a sun, including its rays. Each sun consists of a central ellipse (or circle) and a number of rays protruding from it. The task is to identify each...

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CF 331D1 - Escaping on Beaveractor

CF 331D1 - Escaping on Beaveractor Rating: 2400 Tags: dfs and similar, implementation Solve time: 2m 12s Verified: no Solution Problem Understanding We are asked to simulate the motion of a "Beaveractor" on a square campus of size $b \times b$. The campus contains a set of directional arrows, each either horizontal or vertical, which force the Beaveractor to change its motion direction when it crosses them. The Beaveractor moves...

Practice › Codeforces Solutions › Codeforces Round 192 (Div. 1) ›

CF 329B - Biridian Forest

CF 329B - Biridian Forest Rating: 1500 Tags: dfs and similar, shortest paths Solve time: 1m 46s Verified: yes Solution Problem Understanding We are given a rectangular grid representing the forest. Some cells are blocked by trees, one cell contains our starting position S , one cell contains the exit E , and some cells contain digits. A digit cell represents that many other breeders standing there initially. All breeders...

Practice › Codeforces Solutions › Codeforces Round 191 (Div. 2) ›

CF 327D - Block Tower

CF 327D - Block Tower Rating: 1900 Tags: constructive algorithms, dfs and similar, graphs Solve time: 1m 12s Verified: yes Solution Problem Understanding We are given a 2D grid with n rows and m columns. Each cell is either empty, where we can place a tower, or a hole, where no tower can be built. There are two types of towers: Blue towers, which always contribute 100 population, and Red...

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CF 325E - The Red Button

CF 325E - The Red Button Rating: 2800 Tags: combinatorics, dfs and similar, dsu, graphs, greedy Solve time: 58s Verified: yes Solution Problem Understanding We are asked to find a sequence of node disarmaments for a circular system of size n where node 0 is special. Node 0 must appear twice: first at the start and last at the end. Every other node must appear exactly once. After disarming a...

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CF 325C - Monsters and Diamonds

CF 325C - Monsters and Diamonds Rating: 2600 Tags: dfs and similar, graphs, shortest paths Solve time: 2m 46s Verified: no Solution Problem Understanding Each monster type has one or more split rules. Applying a rule consumes one monster of that type and produces two things: First, some number of diamonds. Second, a multiset of new monsters. Starting from a single monster, we repeatedly choose a rule for every monster...

Practice › Codeforces Solutions › Codeforces Round 190 (Div. 1) ›

CF 321C - Ciel the Commander

CF 321C - Ciel the Commander Rating: 2100 Tags: constructive algorithms, dfs and similar, divide and conquer, greedy, trees Solve time: 1m 6s Verified: yes Solution Problem Understanding We are given a tree with up to 100,000 nodes, and we must assign each node a letter from 'A' to 'Z'. These letters represent ranks, where 'A' is the strongest and 'Z' is the weakest. The constraint is global and pairwise:...

Practice › Codeforces Solutions › Codeforces Round 189 (Div. 2) ›

CF 320B - Ping-Pong (Easy Version)

CF 320B - Ping-Pong (Easy Version) Rating: 1500 Tags: dfs and similar, graphs Solve time: 1m 13s Verified: yes Solution Problem Understanding We are maintaining a growing collection of open intervals on the number line. Each time a new interval is added, it becomes a node in an implicit directed graph. From any interval, we are allowed to move to another interval if one of the endpoints of the first...

Practice › Codeforces Solutions › Codeforces Round 188 (Div. 1) ›

CF 317C - Balance

CF 317C - Balance Rating: 2500 Tags: constructive algorithms, dfs and similar, graphs, trees Solve time: 1m 26s Verified: no Solution Problem Understanding We are given a set of n vessels, each capable of holding up to v liters of water. Some vessels are connected by tubes that allow water to be transferred in integer amounts. Each vessel starts with some initial quantity of water, and we are asked to...

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CF 316F3 - Suns and Rays

CF 316F3 - Suns and Rays Rating: 2200 Tags: constructive algorithms, dfs and similar, implementation Solve time: 57s Verified: yes Solution Problem Understanding The task is to analyze a binary image where 0 represents the background and 1 represents a sun or its rays. Each sun consists of a central ellipse (which may be rotated) and several rays extending outward as line segments from the ellipse’s boundary. We must identify...

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CF 316B2 - EKG

CF 316B2 - EKG Rating: 1600 Tags: dfs and similar, dp Solve time: 1m 3s Verified: yes Solution Problem Understanding We are given a queue of n beavers, each numbered from 1 to n . Each beaver either knows who should be immediately in front of them, represented as a[i] (the number of that beaver), or does not know, represented as 0 . There is no cycle in these dependencies,...

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CF 316B1 - EKG

CF 316B1 - EKG Rating: 1500 Tags: brute force, dfs and similar Solve time: 1m 33s Verified: yes Solution Problem Understanding We are given a structure of people standing in a queue, but the queue is not fully known. Each person either clearly knows who stands immediately in front of them or does not know that information at all. Formally, each person i points to at most one other person...

Practice › Codeforces Solutions › Codeforces Round 187 (Div. 1) ›

CF 314B - Sereja and Periods

CF 314B - Sereja and Periods Rating: 2000 Tags: binary search, dfs and similar, strings Solve time: 1m 5s Verified: yes Solution Problem Understanding We are given two strings, a and c , and two integers, b and d . The string a is repeated b times to form a long string w , and the string c is repeated p times to form another string q . The task...

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Croc Champ 2013 - Round 1

Croc Champ 2013 - Round 1 Special | 5 problems | 5/5 verified | Difficulty 1100-2000 | 9m 28s # Problem Rating Tags Accepted Time ✓ A SMSC 1100 implementation 2,864 1m 35s ✓ B Network Topology 1200 graphs, implementation 10,507 1m 51s ✓ C Beautiful IP Addresses 2000 brute-force 1,312 2m 38s ✓ D Connected Components 1900 data-structures, dfs-and-similar, dp 2,770 2m 11s ✓ E Copying Data 1900 data-structures...

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Codeforces Round 170 (Div. 1)

Codeforces Round 170 (Div. 1) Div. 1 | 5 problems | 2/5 verified | Difficulty 1400-2800 | 9m 3s # Problem Rating Tags Accepted Time ✓ A Learning Languages 1400 dfs-and-similar, dsu 21,564 1m 34s ✓ B Set of Points 2300 constructive-algorithms, geometry 847 1m 51s C Game 2400 games, implementation 491 2m 33s D Google Code Jam 2800 dp, probabilities 372 1m 33s E Binary Tree on Plane 2400...

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Codeforces Round 168 (Div. 1)

Codeforces Round 168 (Div. 1) Div. 1 | 5 problems | 4/5 verified | Difficulty 1500-3000 | 6m 59s # Problem Rating Tags Accepted Time ✓ A k-Multiple Free Set 1500 binary-search, greedy, sortings 10,812 1m 6s ✓ B Zero Tree 1800 dfs-and-similar, dp, greedy 5,570 1m 11s ✓ C The Last Hole! 2600 brute-force, geometry 376 1m 12s ✓ D Lovely Matrix 2200 dfs-and-similar, graphs, greedy 1,155 1m 34s...

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Codeforces Round 177 (Div. 1)

Codeforces Round 177 (Div. 1) Div. 1 | 5 problems | 2/5 verified | Difficulty 1300-2800 | 11m 9s # Problem Rating Tags Accepted Time ✓ A Polo the Penguin and Strings 1300 greedy 6,752 1m 40s ✓ B Polo the Penguin and Houses 1500 combinatorics 3,210 2m 4s C Polo the Penguin and XOR operation 1700 implementation, math 2,457 2m 7s D Polo the Penguin and Trees 2400 combinatorics,...

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April Fools Day Contest 2013

April Fools Day Contest 2013 April Fools | 6 problems | 6/6 verified | Difficulty 1400-2800 | 9m 4s # Problem Rating Tags Accepted Time ✓ A Mysterious strings 1400 *special, implementation 3,236 1m 23s ✓ B QR code 1500 *special, implementation 2,616 1m 1s ✓ C WTF? 1700 *special, graph-matchings, implementation 1,672 2m 7s ✓ D Orange 1400 *special, implementation 1,904 2m 7s ✓ E HQ 2500 *special, constructive-algorithms...

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Codeforces Round 174 (Div. 1)

Codeforces Round 174 (Div. 1) Div. 1 | 5 problems | 3/5 verified | Difficulty 1600-2800 | 9m 44s # Problem Rating Tags Accepted Time ✓ A Cows and Sequence 1600 constructive-algorithms, data-structures, implementation 6,871 1m 46s ✓ B Cow Program 1700 dfs-and-similar, dp, graphs 3,930 1m 36s ✓ C Coin Troubles 2100 dp 1,566 1m 30s ✓ D Cows and Cool Sequences 2400 dp, math, number-theory 641 2m 25s...

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Codeforces Round 181 (Div. 2)

Codeforces Round 181 (Div. 2) Div. 2 | 5 problems | 3/5 verified | Difficulty 1100-2300 | 8m 21s # Problem Rating Tags Accepted Time ✓ A Array 1100 brute-force, constructive-algorithms, implementation 27,175 1m 26s ✓ B Coach 1500 brute-force, dfs-and-similar, graphs 7,148 2m 11s C Beautiful Numbers 1800 brute-force, combinatorics 11,742 1m 15s ✓ D Painting Square 2300 dp, fft 855 1m 48s E Empire Strikes Back 2300 binary-search,...

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Codeforces Round 134 (Div. 1)

Codeforces Round 134 (Div. 1) Div. 1 | 5 problems | 2/5 verified | Difficulty 1200-2900 | 11m 29s # Problem Rating Tags Accepted Time ✓ A Ice Skating 1200 brute-force, dfs-and-similar, dsu 24,319 1m 27s B Blackboard Fibonacci 2100 brute-force, math 1,093 2m 48s ✓ C Formurosa 2600 divide-and-conquer, dp, expression-parsing 368 2m 29s D Bitonix' Patrol 2900 bitmasks, brute-force, combinatorics 273 1m 37s E Alien DNA 2800 data-structures,...

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CF 300B - Coach

CF 300B - Coach Rating: 1500 Tags: brute force, dfs and similar, graphs Solve time: 2m 11s Verified: no Solution Problem Understanding We are asked to divide n students into teams of exactly three. Some students explicitly request to be on the same team with certain other students. These requests are mutual, so if student 2 wants to team with student 5, then student 5 also wants student 2. Our...

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CF 292D - Connected Components

CF 292D - Connected Components Rating: 1900 Tags: data structures, dfs and similar, dp, dsu Solve time: 2m 11s Verified: yes Solution Problem Understanding We have an undirected graph representing a computer network. The vertices are computers and the edges are cables. The cables are numbered from 1 to m in the order they appear in the input. Each query removes a contiguous block of edges, from index l to...

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CF 291E - Tree-String Problem

CF 291E - Tree-String Problem Rating: 2000 Tags: *special, dfs and similar, hashing, strings Solve time: 2m 57s Verified: no Solution Problem Understanding We are given a rooted tree with $n$ vertices, where each edge is labeled with a non-empty string. The root of the tree is vertex 1. Each non-root vertex $v$ has a parent $p_v$ and a string $s_v$ on the edge from $p_v$ to $v$. A "position"...

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CF 290F - Greedy Petya

CF 290F - Greedy Petya Rating: 2800 Tags: *special, dfs and similar, graphs, greedy Solve time: 1m 8s Verified: yes Solution Problem Understanding We are given an undirected graph with up to 20 vertices and up to 400 edges, and we need to decide whether there exists a simple path that visits every vertex exactly once. This is the Hamiltonian path problem in its decision form: we are not asked...

Practice › Codeforces Solutions › Codeforces Round 177 (Div. 1) ›

CF 288D - Polo the Penguin and Trees

CF 288D - Polo the Penguin and Trees Rating: 2400 Tags: combinatorics, dfs and similar, trees Solve time: 2m 14s Verified: no Solution Problem Understanding We are given a tree with n nodes, each node numbered from 1 to n , and n -1 edges connecting them. Polo wants to count pairs of node-to-node paths that do not share any nodes. Concretely, each path is defined by two nodes a...

Practice › Codeforces Solutions › Codeforces Round 174 (Div. 1) ›

CF 283B - Cow Program

CF 283B - Cow Program Rating: 1700 Tags: dfs and similar, dp, graphs Solve time: 1m 36s Verified: yes Solution Problem Understanding We are given a sequence of positive integers of length n where the first element is initially unknown and the remaining n - 1 elements are provided. The "cow program" defines two integer variables, x and y , starting with x = 1 and y = 0. The...

Practice › Codeforces Solutions › Codeforces Round 170 (Div. 1) ›

CF 277A - Learning Languages

CF 277A - Learning Languages Rating: 1400 Tags: dfs and similar, dsu Solve time: 1m 34s Verified: yes Solution Problem Understanding We are asked to ensure that every employee at BerCorp can communicate with every other employee, either directly through a shared language or indirectly via a chain of translators. Each employee may initially know zero or more official languages, and we can pay for them to learn additional languages...

Practice › Codeforces Solutions › Codeforces Round 168 (Div. 1) ›

CF 274B - Zero Tree

CF 274B - Zero Tree Rating: 1800 Tags: dfs and similar, dp, greedy, trees Solve time: 1m 11s Verified: yes Solution Problem Understanding The input describes a tree where every vertex holds an integer value. The only allowed operation is global but structurally restricted: you pick a connected region that must contain vertex 1, and then you add either +1 or -1 to every value in that region. You repeat...

Practice › Codeforces Solutions › Codeforces Round 168 (Div. 1) ›

CF 274D - Lovely Matrix

CF 274D - Lovely Matrix Rating: 2200 Tags: dfs and similar, graphs, greedy, sortings Solve time: 1m 34s Verified: yes Solution Problem Understanding We are given a matrix with n rows and m columns. Each row originally was sorted in non-decreasing order, but now some entries have been erased (marked -1 ) and the columns may have been shuffled. Our task is to restore the column order so that it...

Practice › Codeforces Solutions › Codeforces Round 134 (Div. 1) ›

CF 217D - Bitonix' Patrol

CF 217D - Bitonix' Patrol Rating: 2900 Tags: bitmasks, brute force, combinatorics, dfs and similar, math Solve time: 1m 37s Verified: no Solution Problem Understanding The problem is essentially about circular modular arithmetic and subset sums. We have a circular orbit of n stations, each separated by m miles. Captain Bitonix has a set of fuel tanks, each with a certain capacity. Using a tank moves him exactly that many...

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CF 217A - Ice Skating

CF 217A - Ice Skating Rating: 1200 Tags: brute force, dfs and similar, dsu, graphs Solve time: 1m 27s Verified: no Solution Problem Understanding We are given a set of snow drifts on a 2D grid with integer coordinates. Bajtek can move only in straight lines along the x or y axis, sliding from one drift until he hits another. In other words, two snow drifts are connected if they...

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Codeforces Round 147 (Div. 2)

Codeforces Round 147 (Div. 2) Div. 2 | 5 problems | 4/5 verified | Difficulty 1000-2000 | 15m 38s # Problem Rating Tags Accepted Time ✓ A Free Cash 1000 implementation 29,521 3m 27s ✓ B Young Table 1500 implementation, sortings 2,376 3m 3s C Primes on Interval 1600 binary-search, number-theory, two-pointers 6,643 2m 42s ✓ D T-decomposition 2000 dfs-and-similar, graphs, greedy 618 2m 57s ✓ E Build String 2000...

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CF 258E - Little Elephant and Tree

CF 258E - Little Elephant and Tree Rating: 2400 Tags: data structures, dfs and similar, trees Solve time: 1m 4s Verified: no Solution Problem Understanding We are given a rooted tree with n nodes, where node 1 is the root. Each node contains a list of numbers that starts empty. We then perform m operations. Each operation consists of two nodes, a_i and b_i , and the operation adds the...

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CF 237D - T-decomposition

CF 237D - T-decomposition Rating: 2000 Tags: dfs and similar, graphs, greedy, trees Solve time: 2m 57s Verified: yes Solution Problem Understanding We are given a tree with $n$ nodes, and our goal is to decompose it into another tree, called a T-decomposition. Each node in this decomposition is a non-empty subset of the original nodes, and we must satisfy three conditions. First, all original nodes must appear in at...

Practice › Codeforces Solutions › Codeforces Round 143 (Div. 2) ›

CF 231E - Cactus

CF 231E - Cactus Rating: 2100 Tags: data structures, dfs and similar, dp, graphs, trees Solve time: 2m 35s Verified: no Solution Problem Understanding We are given a connected undirected graph that is guaranteed to be a vertex cactus. In a vertex cactus, every vertex belongs to at most one simple cycle. Cycles may touch the rest of the graph through articulation points, but two different cycles can never share...

Practice › Codeforces Solutions › Codeforces Round 141 (Div. 2) ›

CF 228E - The Road to Berland is Paved With Good Intentions

CF 228E - The Road to Berland is Paved With Good Intentions Rating: 1900 Tags: 2-sat, dfs and similar, dsu, graphs Solve time: 1m 57s Verified: no Solution Problem Understanding We have a graph with n cities connected by m undirected roads. Each road either has asphalt ( 1 ) or does not ( 0 ). The king can pick a city and the workers will toggle the asphalt status...

Practice › Codeforces Solutions › Codeforces Round 139 (Div. 2) ›

CF 225D - Snake

CF 225D - Snake Rating: 2200 Tags: bitmasks, dfs and similar, graphs, implementation Solve time: 2m 19s Verified: no Solution

Practice › Codeforces Solutions › Codeforces Round 135 (Div. 2) ›

CF 219D - Choosing Capital for Treeland

CF 219D - Choosing Capital for Treeland Rating: 1700 Tags: dfs and similar, dp, graphs, trees Solve time: 1m 16s Verified: yes Solution Problem Understanding We are asked to choose a capital city in a tree-shaped country with one-way roads. Each city is a node, and each road is a directed edge. The goal is to orient all roads so that from the chosen capital, we can reach every other...

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Codeforces Round 124 (Div. 1)

Codeforces Round 124 (Div. 1) Div. 1 | 5 problems | 2/5 verified | Difficulty 1100-2800 | 8m 52s # Problem Rating Tags Accepted Time ✓ A Lexicographically Maximum Subsequence 1100 greedy, strings 5,844 1m 29s ✓ B Infinite Maze 2000 dfs-and-similar, graphs 2,376 1m 39s ✓ C Paint Tree 2200 constructive-algorithms, divide-and-conquer, geometry 1,040 1m 40s D The Next Good String 2800 data-structures, greedy, hashing 599 2m 4s E...

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Codeforces Round 130 (Div. 2)

Codeforces Round 130 (Div. 2) Div. 2 | 5 problems | 3/5 verified | Difficulty 900-2100 | 9m 13s # Problem Rating Tags Accepted Time ✓ A Dubstep 900 strings 105,014 1m 16s ✓ B Solitaire 1900 dfs-and-similar, dp 1,496 1m 21s ✓ C Police Station 1900 dp, graphs, shortest-paths 2,151 1m 56s ✓ D Prizes, Prizes, more Prizes 1200 implementation 8,047 2m 50s E Blood Cousins 2100 binary-search, data-structures,...

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Codeforces Round 120 (Div. 2)

Codeforces Round 120 (Div. 2) Div. 2 | 5 problems | 1/5 verified | Difficulty 1100-2100 | 4m 25s # Problem Rating Tags Accepted Time ✓ A Vasya and the Bus 1100 greedy, math 6,259 21s B Surrounded 1800 geometry 3,092 1m 24s ✓ C STL 1500 dfs-and-similar 3,225 43s D Non-Secret Cypher 1900 two-pointers 2,660 24s E Counter Attack 2100 data-structures, dsu, graphs 1,737 1m 33s

Practice › Codeforces Solutions › Codeforces Round 130 (Div. 2) ›

CF 208B - Solitaire

CF 208B - Solitaire Rating: 1900 Tags: dfs and similar, dp Solve time: 1m 21s Verified: yes Solution Problem Understanding We are given a shuffled deck of up to 52 cards arranged in a line, each represented by a value and a suit. Initially, every card forms its own pile. The player can move a pile onto either the pile immediately to its left or the pile three positions to...

Practice › Codeforces Solutions › Codeforces Round 130 (Div. 2) ›

CF 208E - Blood Cousins

CF 208E - Blood Cousins Rating: 2100 Tags: binary search, data structures, dfs and similar, trees Solve time: 1m 50s Verified: no Solution Problem Understanding We are given a rooted forest where each person has at most one parent. If we follow parent pointers upward, we eventually reach a root or fall off the structure. This defines a collection of trees. A “k-th ancestor” means applying the parent relation k...

Practice › Codeforces Solutions › Codeforces Round 120 (Div. 2) ›

CF 190C - STL

CF 190C - STL Rating: 1500 Tags: dfs and similar Solve time: 43s Verified: no Solution Problem Understanding We are given a sequence of tokens that were spoken in order, each token being either int or pair . These tokens are supposed to form a valid nested type expression of a very specific grammar. The grammar is fully binary: every int is a leaf type, and every pair combines exactly...

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CF 177C2 - Party

CF 177C2 - Party Rating: 1500 Tags: brute force, dfs and similar, dsu, graphs Solve time: 1m 14s Verified: yes Solution Problem Understanding We are given a set of people where some pairs are connected by friendship relations and some pairs are in conflict because they dislike each other. Friendship is transitive through chains, so connected components in the friendship graph represent groups that must be treated as inseparable if...

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CF 177C1 - Party

CF 177C1 - Party Rating: 1500 Tags: dfs and similar, dsu, graphs Solve time: 1m 13s Verified: yes Solution Problem Understanding We are given a set of people, where some pairs are friends and some pairs dislike each other. Friendship forms an undirected graph, and dislike forms another set of forbidden edges. The task is to choose a subset of people such that two constraints hold simultaneously. First, if a...

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CF 176E - Archaeology

CF 176E - Archaeology Rating: 3100 Tags: data structures, dfs and similar, trees Solve time: 2m 40s Verified: no Solution Problem Understanding We are given a weighted tree. Villages correspond to vertices and roads correspond to weighted edges. At any moment, only some villages are "alive". Villages can be added and removed over time. After each update, we may be asked for the total length of the roads that are...

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CF 2227H - Fallen Leaves

CF 2227H - Fallen Leaves Rating: - Tags: dfs and similar, dp, trees Solve time: 2m 56s Verified: no Solution Problem Understanding We are given a tree and a fixed set of vertices consisting of all leaves in the original tree. These leaves are determined once from the initial structure and do not change during the process. We then repeatedly pick two distinct unused leaves, add the length of the...

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European Championship 2024 - Online Mirror (Unrated, ICPC Rules, Teams Preferred)

European Championship 2024 - Online Mirror (Unrated, ICPC Rules, Teams Preferred) ICPC/IOI | 11 problems | 4/11 verified | Difficulty 1500-3300 | 26m 7s # Problem Rating Tags Accepted Time ✓ A Grove 3300 brute-force, dfs-and-similar, dp 203 2m 41s ✓ B Charming Meals 1500 binary-search, brute-force, greedy 4,896 1m 44s ✓ C Annual Ants' Gathering 1900 dfs-and-similar, dp, greedy 2,526 4m 48s ✓ D Funny or Scary? 2600 constructive-algorithms...

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CF 1975E - Chain Queries

CF 1975E - Chain Queries Rating: 2100 Tags: binary search, data structures, dfs and similar, implementation, trees Solve time: 5m 17s Verified: no Solution

Practice › Codeforces Solutions › Educational Codeforces Round 166 (Rated for Div. 2) ›

CF 1976E - Splittable Permutations

CF 1976E - Splittable Permutations Rating: 2500 Tags: combinatorics, data structures, dfs and similar, greedy, math, trees Solve time: 5m 16s Verified: no Solution

Practice › Codeforces Solutions › Codeforces Round 947 (Div. 1 + Div. 2) ›

CF 1975D - Paint the Tree

CF 1975D - Paint the Tree Rating: 1700 Tags: brute force, dfs and similar, dp, greedy, shortest paths, trees Solve time: 5m 19s Verified: no Solution

Practice › Codeforces Solutions › Codeforces Round 947 (Div. 1 + Div. 2) ›

CF 1975F - Set

CF 1975F - Set Rating: 2600 Tags: bitmasks, brute force, combinatorics, dfs and similar, divide and conquer, dp, math Solve time: 5m 17s Verified: no Solution

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CF 1949A - Grove

CF 1949A - Grove Rating: 3300 Tags: brute force, dfs and similar, dp, geometry, probabilities Solve time: 2m 41s Verified: yes Solution Problem Understanding Every tree is planted at an integer lattice point. Around that point we place a disk of radius r , representing the root system. Two conditions must hold. The entire disk must stay inside the square lawn. Since the lawn is the square [0,n] × [0,n]...

Practice › Codeforces Solutions › Codeforces Round 934 (Div. 1) ›

CF 1943C - Tree Compass

CF 1943C - Tree Compass Rating: 2300 Tags: constructive algorithms, dfs and similar, greedy, trees Solve time: 1m 16s Verified: no Solution Problem Understanding We are given a tree and an operation that does not act on a single node, but on a layer of nodes: if we pick a center vertex $v$ and a distance $d$, we recolor every vertex whose shortest-path distance from $v$ is exactly $d$. Each...

Practice › Codeforces Solutions › CodeTON Round 8 (Div. 1 + Div. 2, Rated, Prizes!) ›

CF 1942D - Learning to Paint

CF 1942D - Learning to Paint Rating: 2100 Tags: binary search, data structures, dfs and similar, dp, greedy, implementation, sortings Solve time: 1m 30s Verified: no Solution Problem Understanding We are asked to help Elsie evaluate her paintings on a 1D canvas of n cells. Each cell can be painted or left empty, and the painting's beauty is determined by a 2D array a . Specifically, for every maximal contiguous...

Practice › Codeforces Solutions › Educational Codeforces Round 163 (Rated for Div. 2) ›

CF 1948C - Arrow Path

CF 1948C - Arrow Path Rating: 1300 Tags: brute force, constructive algorithms, dfs and similar, dp, graphs, shortest paths Solve time: 56s Verified: yes Solution Problem Understanding We have a 2-row grid with $n$ columns, and each cell contains an arrow pointing either left or right. The robot starts at the top-left corner, and each second it first moves to an adjacent cell (up, down, left, right) and then follows...

Practice › Codeforces Solutions › Codeforces Round 937 (Div. 4) ›

CF 1950G - Shuffling Songs

CF 1950G - Shuffling Songs Rating: 1900 Tags: bitmasks, dfs and similar, dp, graphs, hashing, implementation, strings Solve time: 1m 22s Verified: yes Solution Problem Understanding Each song has two attributes, a genre and a writer. After removing some songs, we are allowed to reorder the remaining songs arbitrarily. The goal is to arrange them so that every pair of neighboring songs shares at least one attribute: either the same...

Practice › Codeforces Solutions › Educational Codeforces Round 166 (Rated for Div. 2) ›

CF 1976F - Remove Bridges

CF 1976F - Remove Bridges Rating: 2800 Tags: data structures, dfs and similar, dp, greedy, sortings, trees Solve time: 5m 17s Verified: no Solution

Practice › Codeforces Solutions › Codeforces Round 942 (Div. 1) ›

CF 1967D - Long Way to be Non-decreasing

CF 1967D - Long Way to be Non-decreasing Rating: 2800 Tags: binary search, dfs and similar, graphs, implementation, shortest paths, two pointers Solve time: 1m 43s Verified: yes Solution Problem Understanding We are given an array where each position contains a value in the range $1$ to $m$, and a second array that defines a deterministic transformation on values: every value $x$ has a fixed replacement $b_x$. One operation, called...

Practice › Codeforces Solutions › Codeforces Round 938 (Div. 3) ›

CF 1955G - GCD on a grid

CF 1955G - GCD on a grid Rating: 1900 Tags: brute force, dfs and similar, dp, implementation, math, number theory Solve time: 1m 6s Verified: yes Solution Problem Understanding We are given a rectangular grid of integers. A move starts at the top-left cell and ends at the bottom-right cell, and at each step we can only go either one cell down or one cell right. Every such move sequence...

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CF 1949C - Annual Ants' Gathering

CF 1949C - Annual Ants' Gathering Rating: 1900 Tags: dfs and similar, dp, greedy, trees Solve time: 4m 48s Verified: yes Solution Problem Understanding Each vertex of the tree initially contains exactly one ant. A move chooses an edge $(u,v)$ and orders all ants currently gathered at $u$ to move to $v$. The ants obey only when the destination already contains at least as many ants as the source. If...

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Codeforces Round 270

Codeforces Round 270 Special | 7 problems | 5/7 verified | Difficulty 800-2800 | 12m 18s # Problem Rating Tags Accepted Time ✓ A Design Tutorial: Learn from Math 800 math, number-theory 70,755 1m 22s ✓ B Design Tutorial: Learn from Life 1300 7,645 1m 44s ✓ C Design Tutorial: Make It Nondeterministic 1400 greedy 6,517 1m 16s ✓ D Design Tutorial: Inverse the Problem 1900 dfs-and-similar, dsu, shortest-paths 6,519...

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Codeforces Round 268 (Div. 1)

Codeforces Round 268 (Div. 1) Div. 1 | 5 problems | 3/5 verified | Difficulty 1500-3100 | 8m 30s # Problem Rating Tags Accepted Time ✓ A 24 Game 1500 constructive-algorithms, greedy, math 8,398 1m 19s ✓ B Two Sets 2000 2-sat, dfs-and-similar, dsu 5,269 2m 32s ✓ C Hack it! 2500 binary-search, constructive-algorithms, math 2,739 1m 18s ✓ D Tree 3100 graph-matchings 476 1m 32s E Permanent 3100 dp,...

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Codeforces Round 267 (Div. 2)

Codeforces Round 267 (Div. 2) Div. 2 | 5 problems | 3/5 verified | Difficulty 800-2400 | 6m 31s # Problem Rating Tags Accepted Time ✓ A George and Accommodation 800 implementation 155,870 1m 1s ✓ B Fedor and New Game 1100 bitmasks, brute-force, constructive-algorithms 42,838 1m 19s ✓ C George and Job 1700 dp, implementation 16,574 1m 35s D Fedor and Essay 2400 dfs-and-similar, dp, graphs 2,030 1m 26s...

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Bayan 2015 Contest Warm Up

Bayan 2015 Contest Warm Up Special | 6 problems | 4/6 verified | Difficulty 1100-2900 | 11m 19s # Problem Rating Tags Accepted Time ✓ A Bayan Bus 1100 implementation 4,931 1m 59s ✓ B Strongly Connected City 1400 brute-force, dfs-and-similar, graphs 9,246 59s ✓ C Kamal-ol-molk's Painting 2100 brute-force, constructive-algorithms, greedy 834 2m 56s D CGCDSSQ 2000 brute-force, data-structures, math 6,507 1m 11s ✓ E Strongly Connected City 2...

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Codeforces Round 264 (Div. 2)

Codeforces Round 264 (Div. 2) Div. 2 | 5 problems | 5/5 verified | Difficulty 1100-2100 | 4m 50s # Problem Rating Tags Accepted Time ✓ A Caisa and Sugar 1200 brute-force, implementation 9,561 1m ✓ B Caisa and Pylons 1100 brute-force, implementation, math 29,962 59s ✓ C Gargari and Bishops 1900 greedy, hashing, implementation 9,179 1m 6s ✓ D Gargari and Permutations 1900 dfs-and-similar, dp, graphs 7,295 58s ✓...

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Codeforces Round 260 (Div. 1)

Codeforces Round 260 (Div. 1) Div. 1 | 5 problems | 5/5 verified | Difficulty 1500-2900 | 7m 50s # Problem Rating Tags Accepted Time ✓ A Boredom 1500 dp 71,930 1m 31s ✓ B A Lot of Games 1900 dfs-and-similar, dp, games 6,839 1m 49s ✓ C Civilization 2100 dfs-and-similar, dp, dsu 6,464 2m 1s ✓ D Serega and Fun 2700 data-structures 3,655 1m 27s ✓ E Function 2900...

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Codeforces Round 259 (Div. 1)

Codeforces Round 259 (Div. 1) Div. 1 | 5 problems | 4/5 verified | Difficulty 1600-3100 | 8m 34s # Problem Rating Tags Accepted Time ✓ A Little Pony and Expected Maximum 1600 probabilities 12,433 1m 46s ✓ B Little Pony and Harmony Chest 2000 bitmasks, brute-force, dp 5,399 1m 19s ✓ C Little Pony and Summer Sun Celebration 2200 constructive-algorithms, dfs-and-similar, graphs 1,742 2m 13s D Little Pony and...

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Codeforces Round 263 (Div. 1)

Codeforces Round 263 (Div. 1) Div. 1 | 5 problems | 3/5 verified | Difficulty 1200-3000 | 8m 20s # Problem Rating Tags Accepted Time ✓ A Appleman and Toastman 1200 greedy, sortings 16,432 2m 14s ✓ B Appleman and Tree 2000 dfs-and-similar, dp, trees 7,017 1m 26s C Appleman and a Sheet of Paper 2200 data-structures, implementation 1,393 1m 22s D Appleman and Complicated Task 2800 dsu, math 401...

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CF 455C - Civilization

CF 455C - Civilization Rating: 2100 Tags: dfs and similar, dp, dsu, ternary search, trees Solve time: 2m 1s Verified: yes Solution Problem Understanding The graph consists of cities connected by roads. The condition that between any two connected cities there is exactly one simple path means every connected component is a tree. Since the graph may be disconnected, the whole graph is a forest. Two types of operations must...

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CF 463E - Caisa and Tree

CF 463E - Caisa and Tree Rating: 2100 Tags: brute force, dfs and similar, math, number theory, trees Solve time: 47s Verified: yes Solution Problem Understanding We are given a rooted tree with n nodes, each node assigned a positive integer value. Node 1 is the root. Queries ask either to find the deepest ancestor of a node v whose value shares a non-trivial greatest common divisor with v ,...

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CF 475E - Strongly Connected City 2

CF 475E - Strongly Connected City 2 Rating: 2700 Tags: dfs and similar Solve time: 2m 26s Verified: yes Solution Problem Understanding We start with a connected undirected graph. Every edge must be assigned a direction. After all directions are chosen, some ordered pairs of vertices $(u,v)$ will satisfy that there is a directed path from $u$ to $v$. The goal is not to make the graph strongly connected. The...

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CF 461B - Appleman and Tree

CF 461B - Appleman and Tree Rating: 2000 Tags: dfs and similar, dp, trees Solve time: 1m 26s Verified: no Solution Problem Understanding We are given a tree with n vertices, where some vertices are black and others are white. The tree is rooted implicitly by the way the edges are described: each node i for i > 0 has a parent p[i-1] . We want to choose a subset...

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CF 453C - Little Pony and Summer Sun Celebration

CF 453C - Little Pony and Summer Sun Celebration Rating: 2200 Tags: constructive algorithms, dfs and similar, graphs Solve time: 2m 13s Verified: no Solution Problem Understanding We are given an undirected graph and, for every vertex, the parity of how many times that vertex must appear in a walk. A walk is represented by a sequence of vertices. Consecutive vertices in the sequence must be connected by an edge....

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CF 455B - A Lot of Games

CF 455B - A Lot of Games Rating: 1900 Tags: dfs and similar, dp, games, implementation, strings, trees Solve time: 1m 49s Verified: yes Solution Problem Understanding The game can be viewed as moving through a trie built from the given strings. We start at the root, which represents the empty string. On each turn a player chooses one outgoing edge, corresponding to appending a character. The current string must...

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CF 472D - Design Tutorial: Inverse the Problem

CF 472D - Design Tutorial: Inverse the Problem Rating: 1900 Tags: dfs and similar, dsu, shortest paths, trees Solve time: 1m 6s Verified: yes Solution Problem Understanding We are given an $n \times n$ matrix where each entry $d[i][j]$ represents the distance between nodes $i$ and $j$. The question asks whether there exists a weighted tree with $n$ nodes such that the distance along the tree between any two nodes...

Practice › Codeforces Solutions › Codeforces Round 273 (Div. 2) ›

CF 478E - Wavy numbers

CF 478E - Wavy numbers Rating: 2900 Tags: brute force, dfs and similar, meet-in-the-middle, sortings Solve time: 1m 37s Verified: no Solution Problem Understanding We are asked to work with a special class of integers defined purely by their digit structure. A number is called “wavy” if, whenever you look at any digit that is not at the boundary, that digit must sit either strictly above both its neighbors or...

Practice › Codeforces Solutions › Codeforces Round 268 (Div. 1) ›

CF 468B - Two Sets

CF 468B - Two Sets Rating: 2000 Tags: 2-sat, dfs and similar, dsu, graph matchings, greedy Solve time: 2m 32s Verified: yes Solution Problem Understanding We are given a set of n distinct integers. Every number must be assigned to one of two groups. If a number x is placed into group A , then its complement with respect to a , namely a - x , must also be...

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CF 463D - Gargari and Permutations

CF 463D - Gargari and Permutations Rating: 1900 Tags: dfs and similar, dp, graphs, implementation Solve time: 58s Verified: yes Solution Problem Understanding We are given k permutations of the numbers from 1 to n . A permutation is simply a rearrangement of these numbers. Our goal is to find the length of the longest sequence of numbers that appears in the same relative order in all k permutations. In...

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CF 475B - Strongly Connected City

CF 475B - Strongly Connected City Rating: 1400 Tags: brute force, dfs and similar, graphs, implementation Solve time: 59s Verified: yes Solution Problem Understanding We are asked to determine if a city with a grid of horizontal and vertical streets is "strongly connected" once each street is made one-way. The city can be visualized as a grid of intersections, with n horizontal streets and m vertical streets forming n ×...

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CF 467D - Fedor and Essay

CF 467D - Fedor and Essay Rating: 2400 Tags: dfs and similar, dp, graphs, hashing, strings Solve time: 1m 26s Verified: no Solution Problem Understanding We are given an essay, which is a sequence of words, and a dictionary of synonym pairs. Each synonym pair allows us to replace one word with another, but only in the direction specified. Fedor wants to modify his essay to minimize the number of...

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Codeforces Round 252 (Div. 2)

Codeforces Round 252 (Div. 2) Div. 2 | 5 problems | 2/5 verified | Difficulty 1000-2400 | 7m 9s # Problem Rating Tags Accepted Time ✓ A Valera and Antique Items 1000 implementation 19,290 1m 21s ✓ B Valera and Fruits 1400 greedy, implementation 7,510 1m 21s ✓ C Valera and Tubes 1500 constructive-algorithms, dfs-and-similar, implementation 11,921 1m 35s D Valera and Swaps 2100 constructive-algorithms, dsu, graphs 1,200 1m 26s...

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Codeforces Round 238 (Div. 1)

Codeforces Round 238 (Div. 1) Div. 1 | 2 problems | 0/2 verified | Difficulty 2200-2800 | 6m 36s # Problem Rating Tags Accepted Time ✓ D Hill Climbing 2200 dfs-and-similar, geometry, trees 1,281 2m 13s E Hamming Triples 2800 implementation, math, two-pointers 272 4m 23s

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Codeforces Round 244 (Div. 2)

Codeforces Round 244 (Div. 2) Div. 2 | 5 problems | 5/5 verified | Difficulty 800-2200 | 7m 50s # Problem Rating Tags Accepted Time ✓ A Police Recruits 800 implementation 97,206 1m 22s ✓ B Prison Transfer 1100 data-structures, implementation 15,510 1m 33s ✓ C Checkposts 1700 dfs-and-similar, graphs, two-pointers 16,884 1m 34s ✓ D Match & Catch 2200 dp, string-suffix-structures, strings 2,423 1m 27s ✓ E Police Patrol...

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Codeforces Round 254 (Div. 2)

Codeforces Round 254 (Div. 2) Div. 2 | 2 problems | 2/2 verified | Difficulty 1200-1400 | 3m 10s # Problem Rating Tags Accepted Time ✓ A DZY Loves Chessboard 1200 dfs-and-similar, implementation 33,654 1m 21s ✓ B DZY Loves Chemistry 1400 dfs-and-similar, dsu, greedy 14,750 1m 49s ✓

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Codeforces Round 245 (Div. 1)

Codeforces Round 245 (Div. 1) Div. 1 | 5 problems | 5/5 verified | Difficulty 1300-3000 | 6m 47s # Problem Rating Tags Accepted Time ✓ A Xor-tree 1300 dfs-and-similar, trees 12,265 1m 38s ✓ B Working out 1600 dp 10,211 57s ✓ C Guess the Tree 2300 bitmasks, constructive-algorithms, dp 1,030 1m 26s ✓ D Tricky Function 2200 data-structures, divide-and-conquer, geometry 3,231 1m 9s ✓ E Points and Segments...

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Codeforces Testing Round 5

Codeforces Testing Round 5 Special | 3 problems | 2/3 verified | Difficulty 900-2700 | 6m 13s # Problem Rating Tags Accepted Time ✓ A Subtractions 900 math, number-theory 9,557 2m 41s ✓ B Dominoes 2000 dfs-and-similar, graphs 753 1m 39s ✓ C Berland Traffic 2700 math, matrices 253 1m 53s

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MemSQL start[c]up Round 1

MemSQL start[c]up Round 1 Special | 5 problems | 3/5 verified | Difficulty 1500-2900 | 11m 24s # Problem Rating Tags Accepted Time ✓ A Square and Rectangles 1500 implementation 2,301 4m 20s ✓ B Stadium and Games 1800 binary-search, math 1,674 1m 50s ✓ C Monsters and Diamonds 2600 dfs-and-similar, graphs, shortest-paths 448 2m 46s D Reclamation 2900 dsu 579 1m 30s E The Red Button 2800 combinatorics, dfs-and-similar,...

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Codeforces Round 161 (Div. 2)

Codeforces Round 161 (Div. 2) Div. 2 | 5 problems | 1/5 verified | Difficulty 800-2500 | 14m 52s # Problem Rating Tags Accepted Time ✓ A Beautiful Matrix 800 implementation 317,750 1m 31s B Squares 900 greedy, implementation, sortings 9,778 3m 7s C Circle of Numbers 2000 brute-force, dfs-and-similar, implementation 1,135 1m 10s ✓ D Cycle in Graph 1800 dfs-and-similar, graphs 4,477 2m 57s E Rhombus 2500 brute-force, data-structures,...

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Codeforces Round 149 (Div. 2)

Codeforces Round 149 (Div. 2) Div. 2 | 5 problems | 3/5 verified | Difficulty 1100-2100 | 12m 58s # Problem Rating Tags Accepted Time ✓ A Heads or Tails 1100 brute-force, implementation 6,792 3m 26s ✓ B Big Segment 1100 implementation, sortings 17,356 1m 12s ✓ C King's Path 1800 dfs-and-similar, graphs, hashing 10,918 3m 11s D Dispute 2100 dfs-and-similar, graphs, greedy 2,032 1m 37s E XOR on Segment...

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Codeforces Round 148 (Div. 1)

Codeforces Round 148 (Div. 1) Div. 1 | 5 problems | 4/5 verified | Difficulty 1300-2900 | 16m 8s # Problem Rating Tags Accepted Time ✓ A Not Wool Sequences 1300 constructive-algorithms, math 2,184 5m 18s ✓ B Boring Partition 1800 constructive-algorithms 1,420 3m 56s ✓ C World Eater Brothers 2100 dfs-and-similar, dp, greedy 1,366 2m 5s ✓ D Tape Programming 2900 data-structures, implementation 268 1m 30s ✓ E Meeting...

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Codeforces Round 150 (Div. 1)

Codeforces Round 150 (Div. 1) Div. 1 | 5 problems | 2/5 verified | Difficulty 1600-3000 | 11m 4s # Problem Rating Tags Accepted Time ✓ A The Brand New Function 1600 bitmasks 4,464 1m 27s ✓ B Hydra 2000 graphs, sortings 1,328 3m 20s C Colorado Potato Beetle 2200 dfs-and-similar, implementation 563 1m 37s D Cubes 2700 data-structures, dp, geometry 232 3m 9s ✓ E Matrix 3000 data-structures 216...

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Codeforces Round 150 (Div. 2)

Codeforces Round 150 (Div. 2) Div. 2 | 2 problems | 1/2 verified | Difficulty 900-1600 | 4m 21s # Problem Rating Tags Accepted Time ✓ A Dividing Orange 900 implementation 8,564 3m 13s B Undoubtedly Lucky Numbers 1600 bitmasks, brute-force, dfs-and-similar 4,931 1m 8s ✓

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Codeforces Round 151 (Div. 2)

Codeforces Round 151 (Div. 2) Div. 2 | 5 problems | 5/5 verified | Difficulty 900-2400 | 6m 57s # Problem Rating Tags Accepted Time ✓ A Buggy Sorting 900 constructive-algorithms, greedy, sortings 10,225 1m 8s ✓ B Increase and Decrease 1300 greedy, math 12,267 58s ✓ C Beauty Pageant 1600 brute-force, constructive-algorithms, greedy 2,829 1m 43s ✓ D Colorful Graph 1600 brute-force, dfs-and-similar, graphs 10,286 1m 30s ✓ E...

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Codeforces Round 145 (Div. 1, ACM-ICPC Rules)

Codeforces Round 145 (Div. 1, ACM-ICPC Rules) Div. 1 | 2 problems | 2/2 verified | Difficulty 2600-2800 | 3m 3s # Problem Rating Tags Accepted Time ✓ E Road Repairs 2800 dfs-and-similar, graphs, greedy 430 1m 58s ✓ F TorCoder 2600 data-structures 2,259 1m 5s ✓

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Codeforces Round 135 (Div. 2)

Codeforces Round 135 (Div. 2) Div. 2 | 5 problems | 5/5 verified | Difficulty 1000-2200 | 6m 25s # Problem Rating Tags Accepted Time ✓ A k-String 1000 implementation, strings 32,297 1m 22s ✓ B Special Offer! Super Price 999 Bourles! 1400 implementation 6,150 1m 29s ✓ C Color Stripe 1600 brute-force, dp, greedy 7,156 1m 3s ✓ D Choosing Capital for Treeland 1700 dfs-and-similar, dp, graphs 12,478 1m...

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Codeforces Round 133 (Div. 2)

Codeforces Round 133 (Div. 2) Div. 2 | 5 problems | 3/5 verified | Difficulty 1200-2000 | 7m 31s # Problem Rating Tags Accepted Time ✓ A Tiling with Hexagons 1200 implementation, math 5,270 56s ✓ B Forming Teams 1700 dfs-and-similar, implementation 7,026 1m 27s ✓ C Hiring Staff 1800 greedy 1,927 2m 5s D Spider's Web 1700 binary-search, sortings, two-pointers 1,499 1m 26s E Martian Luck 2000 math, number-theory...

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Codeforces Round 131 (Div. 1)

Codeforces Round 131 (Div. 1) Div. 1 | 5 problems | 3/5 verified | Difficulty 1700-2700 | 7m 23s # Problem Rating Tags Accepted Time ✓ A Game 1700 dfs-and-similar, greedy 1,889 52s ✓ B Numbers 1900 combinatorics, dp 1,979 54s C Relay Race 2000 dp 3,254 2m 58s ✓ D Stars 2300 constructive-algorithms, geometry 363 1m 36s E Two Permutations 2700 data-structures, hashing, strings 967 1m 3s ✓

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Codeforces Round 121 (Div. 1)

Codeforces Round 121 (Div. 1) Div. 1 | 5 problems | 5/5 verified | Difficulty 1500-2700 | 8m 55s # Problem Rating Tags Accepted Time ✓ A Dynasty Puzzles 1500 dp 4,553 1m 42s ✓ B Demonstration 1700 greedy 1,101 1m 33s ✓ C Fools and Roads 1900 data-structures, dfs-and-similar, trees 9,215 1m 55s ✓ D Metro Scheme 2700 graphs, greedy 392 1m 59s ✓ E Thwarting Demonstrations 2200 binary-search,...

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Codeforces Round 119 (Div. 1)

Codeforces Round 119 (Div. 1) Div. 1 | 5 problems | 4/5 verified | Difficulty 1500-2900 | 10m 3s # Problem Rating Tags Accepted Time ✓ A Permutations 1500 greedy 3,042 1m 30s ✓ B AlgoRace 1800 dp, shortest-paths 2,344 2m 5s ✓ C Weak Memory 2000 dfs-and-similar, dsu 1,578 2m 12s ✓ D BRT Contract 2800 data-structures 583 1m 54s ✓ E Heaven Tour 2900 data-structures, greedy 117 2m...

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Croc Champ 2012 - Qualification Round

Croc Champ 2012 - Qualification Round Special | 5 problems | 4/5 verified | Difficulty 800-2200 | 11m 42s # Problem Rating Tags Accepted Time ✓ A Phone Code 800 *special, brute-force, implementation 7,513 3m ✓ B Pseudorandom Sequence Period 1200 *special, implementation, number-theory 3,153 3m 33s ✓ C Bus 1500 *special, implementation, sortings 1,259 1m 19s ✓ D Calendar Reform 1500 *special, number-theory 1,518 1m 29s ✓ E BHTML+BCSS...

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Croc Champ 2012 - Final

Croc Champ 2012 - Final Special | 5 problems | 5/5 verified | Difficulty 1700-2900 | 10m 12s # Problem Rating Tags Accepted Time ✓ A Headquarters 1700 constructive-algorithms, math 664 1m 52s ✓ B Zoo 1700 brute-force, geometry 847 1m 27s ✓ C Cyclic Coloring 2200 dfs-and-similar 727 3m 32s ✓ D T-shirt 2700 dp, greedy, probabilities 481 1m 15s ✓ E Candy Shop 2900 greedy 186 2m 6s...

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ABBYY Cup 2.0 - Easy

ABBYY Cup 2.0 - Easy Special | 14 problems | 7/14 verified | Difficulty 800-2600 | 22m 32s # Problem Rating Tags Accepted Time ✓ A1 Good Matrix Elements 800 implementation 11,501 1m 37s A2 Good Matrix Elements 800 implementation 8,564 3m 13s ✓ B1 Rectangular Game 1000 number-theory 5,100 4m 29s B2 Rectangular Game 1200 number-theory 3,361 1m 40s ✓ C1 Party 1500 dfs-and-similar, dsu, graphs 2,997 1m 13s...

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Croc Champ 2012 - Round 1

Croc Champ 2012 - Round 1 Special | 5 problems | 3/5 verified | Difficulty 1300-2600 | 10m 55s # Problem Rating Tags Accepted Time ✓ A Rock-Paper-Scissors 1300 implementation, math 2,512 1m 40s ✓ B Chamber of Secrets 1800 dfs-and-similar, shortest-paths 3,986 1m 49s ✓ C Spiral Maximum 1900 brute-force, dp 1,112 2m 41s D Deputies 2500 constructive-algorithms, graphs, greedy 289 3m 4s ✓ E Camping Groups 2600 data-structures,...

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VK Cup 2012 Round 3

VK Cup 2012 Round 3 Special | 5 problems | 3/5 verified | Difficulty 1700-3100 | 9m 50s # Problem Rating Tags Accepted Time ✓ A Variable, or There and Back Again 1700 dfs-and-similar, graphs 1,197 1m 51s ✓ B Ancient Berland Hieroglyphs 2000 two-pointers 529 1m 30s ✓ C Machine Programming 2400 flows, graphs 981 2m 16s ✓ D Minimum Diameter 3100 binary-search, brute-force 276 2m 18s E Polycarpus...

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Codeforces Round 111 (Div. 2)

Codeforces Round 111 (Div. 2) Div. 2 | 5 problems | 5/5 verified | Difficulty 900-2400 | 8m 5s # Problem Rating Tags Accepted Time ✓ A Twins 900 greedy, sortings 143,576 1m 15s ✓ B Unlucky Ticket 1100 greedy, sortings 15,550 1m 29s ✓ C Find Pair 1700 implementation, math, sortings 3,719 1m 47s ✓ D Edges in MST 2300 dfs-and-similar, dsu, graphs 3,350 1m 21s ✓ E Buses...

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Codeforces Round 107 (Div. 1)

Codeforces Round 107 (Div. 1) Div. 1 | 5 problems | 4/5 verified | Difficulty 1400-3000 | 11m 8s # Problem Rating Tags Accepted Time ✓ A Win or Freeze 1400 games, math, number-theory 8,591 2m 2s B Quantity of Strings 1600 combinatorics, dfs-and-similar, graphs 5,314 1m 40s ✓ C Smart Cheater 2200 data-structures, math, probabilities 746 2m 11s ✓ D Mission Impassable 2600 dp, strings 738 2m 26s ✓...

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Codeforces Round 103 (Div. 2)

Codeforces Round 103 (Div. 2) Div. 2 | 5 problems | 5/5 verified | Difficulty 800-2200 | 8m 5s # Problem Rating Tags Accepted Time ✓ A Arrival of the General 800 implementation 121,315 1m 52s ✓ B Meeting 1300 implementation 5,684 1m 15s ✓ C Anagram Search 1500 implementation, strings 4,264 1m 23s ✓ D Missile Silos 1900 data-structures, dfs-and-similar, graphs 5,030 2m 10s ✓ E Competition 2200 data-structures,...

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CF 161D - Distance in Tree

CF 161D - Distance in Tree Rating: 1800 Tags: dfs and similar, dp, trees Solve time: 3m 13s Verified: yes Solution Problem Understanding We are given a tree with n vertices, meaning a connected graph with no cycles, and a number k . The task is to count how many pairs of distinct vertices are separated by exactly k edges. Every edge in the tree connects two vertices directly, and...

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CF 160D - Edges in MST

CF 160D - Edges in MST Rating: 2300 Tags: dfs and similar, dsu, graphs, sortings Solve time: 1m 21s Verified: yes Solution Problem Understanding We are given a connected weighted undirected graph with no loops or multiple edges. Each edge has a positive weight. The task is to classify each edge according to whether it belongs to all minimum spanning trees, at least one minimum spanning tree, or no minimum...

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CF 150B - Quantity of Strings

CF 150B - Quantity of Strings Rating: 1600 Tags: combinatorics, dfs and similar, graphs, math Solve time: 1m 40s Verified: yes Solution Problem Understanding We want to count strings of length n built from an alphabet of size m , under one strong restriction: every substring of length k must be a palindrome. A substring of length k starting at position i contains characters $$s_i, s_{i+1}, \dots, s_{i+k-1}$$ and being...

Practice › Codeforces Solutions › Codeforces Round 161 (Div. 2) ›

CF 263D - Cycle in Graph

CF 263D - Cycle in Graph Rating: 1800 Tags: dfs and similar, graphs Solve time: 2m 57s Verified: no Solution Problem Understanding We are given an undirected graph where every vertex has a very strong local condition: each node is connected to at least $k$ other distinct nodes. From this structure we are asked to extract a simple cycle whose length is not just positive, but at least $k+1$. The...

Practice › Codeforces Solutions › Codeforces Round 242 (Div. 2) ›

CF 424E - Colored Jenga

CF 424E - Colored Jenga Rating: 2500 Tags: dfs and similar, dp, probabilities Solve time: 6m 29s Verified: no Solution Problem Understanding We are given a vertical stack of levels, each level containing three colored blocks arranged left, middle, right. The tower has a physical constraint: it is only stable if every non-top level has at least one remaining block, and additionally a level is unstable if it is reduced...

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CF 242C - King's Path

CF 242C - King's Path Rating: 1800 Tags: dfs and similar, graphs, hashing, shortest paths Solve time: 3m 11s Verified: no Solution Problem Understanding We are given a huge implicit grid, up to $10^9 \times 10^9$, but only a small subset of cells are usable. Each usable region is given as a horizontal segment: a row number and a contiguous interval of columns. Taken together, these segments define a sparse...

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CF 191C - Fools and Roads

CF 191C - Fools and Roads Rating: 1900 Tags: data structures, dfs and similar, trees Solve time: 1m 55s Verified: yes Solution Problem Understanding The input describes a tree of cities. Since there is exactly one simple path between every pair of cities, the road network forms a connected acyclic graph. Then we are given several pairs of cities. Each pair represents one trip: a fool travels from city a...

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CF 213A - Game

CF 213A - Game Rating: 1700 Tags: dfs and similar, greedy Solve time: 52s Verified: yes Solution Problem Understanding We are given a game split into n parts. Each part must be completed on a specific computer, and some parts depend on others, forming a dependency graph without cycles. Rubik can start at any computer and spends exactly one hour to complete a part. Moving between computers has asymmetric costs:...

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CF 167E - Wizards and Bets

CF 167E - Wizards and Bets Rating: 2900 Tags: dfs and similar, graphs, math, matrices Solve time: 3m 52s Verified: yes Solution Problem Understanding We are given a directed acyclic graph. Some vertices are sources, meaning no edge enters them. Some vertices are sinks, meaning no edge leaves them. The number of sources and sinks is guaranteed to be equal. A valid configuration consists of vertex-disjoint directed paths such that...

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CF 173B - Chamber of Secrets

CF 173B - Chamber of Secrets Rating: 1800 Tags: dfs and similar, shortest paths Solve time: 1m 49s Verified: yes Solution Problem Understanding The Chamber of Secrets is represented as a grid of size n by m , where each cell is either empty or contains a column. A basilisk is stationed in the bottom-right corner and looks left, while a person trying to enter starts at the top-left corner...

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CF 427C - Checkposts

CF 427C - Checkposts Rating: 1700 Tags: dfs and similar, graphs, two pointers Solve time: 1m 34s Verified: yes Solution Problem Understanding We are given a directed graph where each node represents a city junction, and each directed edge represents a one-way road. Each junction has a cost to build a police checkpost. A checkpost at junction i protects all junctions reachable from i and able to return to i...

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CF 254D - Rats

CF 254D - Rats Rating: 2300 Tags: brute force, dfs and similar, graphs, implementation, shortest paths Solve time: 3m 1s Verified: no Solution Problem Understanding The problem presents a rectangular basement of a store as an n × m grid, where some cells are walls, some are empty, and some contain sleeping rats. Vasily has two grenades, and when a grenade explodes in a cell, its blast propagates outward to...

Practice › Codeforces Solutions › Codeforces Round 133 (Div. 2) ›

CF 216B - Forming Teams

CF 216B - Forming Teams Rating: 1700 Tags: dfs and similar, implementation Solve time: 1m 27s Verified: yes Solution Problem Understanding We can model the students as an undirected graph. Each student is a vertex, and every pair of enemies creates an edge. We want to split the remaining students into two teams of equal size such that no edge stays inside one team. In graph terms, we need a...

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CF 243C - Colorado Potato Beetle

CF 243C - Colorado Potato Beetle Rating: 2200 Tags: dfs and similar, implementation Solve time: 1m 37s Verified: no Solution Problem Understanding We are working on an enormous infinite grid of unit square cells, and we can think of each cell as a “bed” in a potato field. We start in the center cell and walk according to a sequence of axis-aligned moves. Every time we move, we do not...

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CF 246D - Colorful Graph

CF 246D - Colorful Graph Rating: 1600 Tags: brute force, dfs and similar, graphs Solve time: 1m 30s Verified: yes Solution Problem Understanding We are given an undirected graph where each vertex has a color, represented by an integer. The goal is to determine which color has the most diverse set of neighboring colors. Formally, for each color $k$, we look at all vertices of that color and collect the...

Practice › Codeforces Solutions › Codeforces Round 112 (Div. 2) ›

CF 165E - Compatible Numbers

CF 165E - Compatible Numbers Rating: 2200 Tags: bitmasks, brute force, dfs and similar, dp Solve time: 1m 47s Verified: yes Solution Problem Understanding We are given an array of integers, and for every element we must find another array element whose bitwise AND with it is zero. Two numbers are compatible exactly when they do not share any bit set to 1 . For example, if we look at...

Practice › Codeforces Solutions › Codeforces Round 245 (Div. 1) ›

CF 429A - Xor-tree

CF 429A - Xor-tree Rating: 1300 Tags: dfs and similar, trees Solve time: 1m 38s Verified: yes Solution Problem Understanding We are given a rooted tree with n nodes, each node labeled with a 0 or 1. We are also given a target configuration of 0s and 1s for each node. The only operation allowed is to "pick" a node, which flips its value and every second-level descendant down the...

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CF 212E - IT Restaurants

CF 212E - IT Restaurants Rating: 1500 Tags: dfs and similar, dp, trees Solve time: 2m 58s Verified: no Solution Problem Understanding We are asked to place two types of restaurants on a tree-shaped city map in such a way that no two adjacent junctions host different types, each junction hosts at most one restaurant, and each network has at least one restaurant. The goal is to maximize the total...

Practice › Codeforces Solutions › Codeforces Testing Round 5 ›

CF 267B - Dominoes

CF 267B - Dominoes Rating: 2000 Tags: dfs and similar, graphs Solve time: 1m 39s Verified: yes Solution Problem Understanding We are given a set of domino tiles, each with two numbers on its halves. The task is to arrange all dominoes in a sequence so that the touching halves of adjacent dominoes have the same number. A domino can be flipped, which swaps its two numbers. The output is...

Practice › Codeforces Solutions › Croc Champ 2012 - Qualification Round ›

CF 172E - BHTML+BCSS

CF 172E - BHTML+BCSS Rating: 2200 Tags: *special, dfs and similar, expression parsing Solve time: 2m 21s Verified: no Solution Problem Understanding We are given a simplified HTML-like document. Every tag is either an opening tag like <a> , a closing tag like </a> , or a self-closing tag like <a/> . The document is guaranteed to be properly nested, so every opening tag has exactly one matching closing tag....

Practice › Codeforces Solutions › Codeforces Round 254 (Div. 2) ›

CF 445A - DZY Loves Chessboard

CF 445A - DZY Loves Chessboard Rating: 1200 Tags: dfs and similar, implementation Solve time: 1m 21s Verified: yes Solution Problem Understanding We are given a chessboard represented as an n by m grid where each cell is either good or bad. A good cell is indicated by a "." and a bad cell by a "-". On every good cell, we must place a chessman that is either white...

Practice › Codeforces Solutions › Codeforces Round 119 (Div. 1) ›

CF 187C - Weak Memory

CF 187C - Weak Memory Rating: 2000 Tags: dfs and similar, dsu Solve time: 2m 12s Verified: yes Solution Problem Understanding We have an undirected graph representing intersections and roads inside the park. Some intersections contain volunteers. PMP starts at intersection s , and the bus station is at intersection t . PMP has weak memory. After talking to a volunteer, he can only remember a path containing at most...

Practice › Codeforces Solutions › Codeforces Round 154 (Div. 2) ›

CF 253C - Text Editor

CF 253C - Text Editor Rating: 1600 Tags: data structures, dfs and similar, graphs, greedy, shortest paths Solve time: 53s Verified: yes Solution Problem Understanding We are given a text editor that stores several lines of text. Each line has a known length, and the cursor is allowed to sit not only on characters but also in the gap positions before the first character and after the last character. So...

Practice › Codeforces Solutions › Codeforces Round 149 (Div. 2) ›

CF 242D - Dispute

CF 242D - Dispute Rating: 2100 Tags: dfs and similar, graphs, greedy Solve time: 1m 37s Verified: no Solution Problem Understanding We are given a graph of counters, where each counter starts at zero and is connected by undirected wires. Pressing a button on a counter increases its own value by one, and also increases the value of every directly connected neighbor by one. We are allowed to choose a...

Practice › Codeforces Solutions › Codeforces Round 103 (Div. 2) ›

CF 144D - Missile Silos

CF 144D - Missile Silos Rating: 1900 Tags: data structures, dfs and similar, graphs, shortest paths Solve time: 2m 10s Verified: yes Solution Problem Understanding We are given a connected weighted undirected graph representing cities and roads. City s is the capital. A missile silo may be located either exactly on a city or at some interior point of a road. A position is valid if its shortest-path distance to...

Practice › Codeforces Solutions › Codeforces Round 206 (Div. 1) ›

CF 354E - Lucky Number Representation

CF 354E - Lucky Number Representation Rating: 2200 Tags: constructive algorithms, dfs and similar, dp Solve time: 5m 13s Verified: no Solution Problem Understanding The problem asks us to express each of a set of positive integers as a sum of exactly six numbers that only contain the digits 0, 4, or 7. These “lucky” numbers include zero, so numbers like 0, 4, 40, 47, 400, or 7074 are all...

Practice › Codeforces Solutions › Codeforces Round 124 (Div. 1) ›

CF 196B - Infinite Maze

CF 196B - Infinite Maze Rating: 2000 Tags: dfs and similar, graphs Solve time: 1m 39s Verified: yes Solution Problem Understanding We are given a finite maze of size n × m . Some cells are walls, some are open, and one cell contains the starting position S . The maze is not used only once. Instead, the entire grid is repeated infinitely in every direction, like tiling the plane...

Practice › Codeforces Solutions › Codeforces Round 150 (Div. 2) ›

CF 244B - Undoubtedly Lucky Numbers

CF 244B - Undoubtedly Lucky Numbers Rating: 1600 Tags: bitmasks, brute force, dfs and similar Solve time: 1m 8s Verified: yes Solution Problem Understanding We are given a single positive integer $n$, and we need to count how many integers from 1 up to $n$ have a very specific property: there exists a pair of digits $x$ and $y$ such that every digit in the number’s decimal representation is either...

Practice › Codeforces Solutions › Coder-Strike 2014 - Round 1 ›

CF 412D - Giving Awards

CF 412D - Giving Awards Rating: 2000 Tags: dfs and similar Solve time: 1m 55s Verified: yes Solution Problem Understanding We have a directed graph of debts. An edge a -> b means employee a owes money to employee b . We must arrange all employees in a sequence such that for every pair of consecutive employees (x, y) in the sequence, there is no edge x -> y ....

Practice › Codeforces Solutions › Codeforces Round 148 (Div. 1) ›

CF 238C - World Eater Brothers

CF 238C - World Eater Brothers Rating: 2100 Tags: dfs and similar, dp, greedy, trees Solve time: 2m 5s Verified: yes Solution Problem Understanding We are given a world of n countries connected by n-1 directed roads. Ignoring the direction of these roads, the countries form a tree. Each brother wants to establish rule in some country and can control every country reachable via directed roads. The problem asks for...

Practice › Codeforces Solutions › Codeforces Round 151 (Div. 2) ›

CF 246E - Blood Cousins Return

CF 246E - Blood Cousins Return Rating: 2400 Tags: binary search, data structures, dfs and similar, dp, sortings Solve time: 1m 38s Verified: yes Solution Problem Understanding We are given a rooted forest describing family relations. Every person has a name and at most one parent. Multiple roots are allowed because some people may have no ancestor at all. For each query (v, k) , we need the number of...

Practice › Codeforces Solutions › Codeforces Round 161 (Div. 2) ›

CF 263C - Circle of Numbers

CF 263C - Circle of Numbers Rating: 2000 Tags: brute force, dfs and similar, implementation Solve time: 1m 10s Verified: yes Solution Problem Understanding We are given a hidden cyclic arrangement of the integers from 1 to n placed around a circle. From this arrangement, someone constructed a set of ordered pairs describing connections between values. These connections come from a simple geometric rule: two numbers are connected if they...

Practice › Codeforces Solutions › Croc Champ 2012 - Final ›

CF 183C - Cyclic Coloring

CF 183C - Cyclic Coloring Rating: 2200 Tags: dfs and similar Solve time: 3m 32s Verified: yes Solution Problem Understanding We have a directed graph where every edge enforces a strict relationship between the colors of its endpoints. If a vertex has color c , then every outgoing neighbor must have color c + 1 , wrapping around modulo k . Another way to write the condition is: $color(v) \equiv...

Practice › Codeforces Solutions › Codeforces Round 238 (Div. 1) ›

CF 406D - Hill Climbing

CF 406D - Hill Climbing Rating: 2200 Tags: dfs and similar, geometry, trees Solve time: 2m 13s Verified: no Solution Problem Understanding We are given a sequence of hills placed along a line. Each hill has a fixed horizontal position and a height, and we imagine it as a vertical segment rising from the ground. From the top of a hill, you can “see” another hill if the straight segment...

Practice › Codeforces Solutions › Codeforces Round 153 (Div. 1) ›

CF 251E - Tree and Table

CF 251E - Tree and Table Rating: 3000 Tags: dfs and similar, dp, implementation, trees Solve time: 1m 57s Verified: no Solution Problem Understanding We are given a tree with $2n$ nodes, and the goal is to place each node into a 2-row by $n$-column table so that each edge of the tree connects two cells sharing a side. Each node occupies exactly one cell, and each cell contains exactly...

Practice › Codeforces Solutions › Codeforces Round 145 (Div. 1, ACM-ICPC Rules) ›

CF 240E - Road Repairs

CF 240E - Road Repairs Rating: 2800 Tags: dfs and similar, graphs, greedy Solve time: 1m 58s Verified: yes Solution Problem Understanding We have a directed graph of cities and roads. City 1 is the capital. Every road is either already usable or broken. A broken road may be repaired, after which it behaves like a normal directed edge. The government wants every city to become reachable from the capital....

Practice › Codeforces Solutions › VK Cup 2012 Round 2 ›

CF 163E - e-Government

CF 163E - e-Government Rating: 2800 Tags: data structures, dfs and similar, dp, strings, trees Solve time: 2m 16s Verified: yes Solution Problem Understanding We have a fixed set of surnames. Each surname can be either active or inactive. Initially every surname is active. The system must process three kinds of operations. A query +i activates the i-th surname. A query -i deactivates the i-th surname. A query ?text asks...

Practice › Codeforces Solutions › VK Cup 2012 Round 3 ›

CF 164A - Variable, or There and Back Again

CF 164A - Variable, or There and Back Again Rating: 1700 Tags: dfs and similar, graphs Solve time: 1m 51s Verified: yes Solution Problem Understanding We are given a directed graph where every node represents a program state. Each state does one of three things to a variable: 0 means the variable is ignored. 1 means the variable is assigned a new value. 2 means the variable is used. A...

Practice › Codeforces Solutions ›

Codeforces Testing Round 3

Codeforces Testing Round 3 Special | 3 problems | 2/3 verified | Difficulty 1200-2200 | 5m 24s # Problem Rating Tags Accepted Time ✓ A Average Numbers 1200 brute-force, implementation 4,792 1m 39s ✓ B Pairs of Numbers 1900 brute-force, dfs-and-similar, math 2,483 1m 30s ✓ C Swaps 2200 constructive-algorithms, graphs, greedy 575 2m 15s

Practice › Codeforces Solutions ›

Codeforces Beta Round 95 (Div. 2)

Codeforces Beta Round 95 (Div. 2) Div. 2 | 6 problems | 5/6 verified | Difficulty 1000-2000 | 10m 6s # Problem Rating Tags Accepted Time ✓ A cAPS lOCK 1000 implementation, strings 100,943 1m 16s ✓ B Opposites Attract 1200 implementation, math 7,548 1m 34s ✓ C The World is a Theatre 1400 combinatorics, math 12,581 1m 35s ✓ D Subway 1600 dfs-and-similar, graphs 5,265 1m 14s ✓ E...

Practice › Codeforces Solutions ›

Codeforces Beta Round 94 (Div. 2 Only)

Codeforces Beta Round 94 (Div. 2 Only) Div. 2 | 2 problems | 2/2 verified | Difficulty 900-1200 | 3m 59s # Problem Rating Tags Accepted Time ✓ A Cookies 900 implementation 25,206 1m 44s ✓ B Students and Shoelaces 1200 brute-force, dfs-and-similar, graphs 13,861 2m 15s ✓

Practice › Codeforces Solutions ›

Codeforces Beta Round 94 (Div. 1 Only)

Codeforces Beta Round 94 (Div. 1 Only) Div. 1 | 5 problems | 5/5 verified | Difficulty 1500-2900 | 8m 36s # Problem Rating Tags Accepted Time ✓ A Statues 1500 dfs-and-similar 3,508 2m 10s ✓ B String 2100 brute-force, constructive-algorithms, hashing 2,869 1m 21s ✓ C Games with Rectangle 2000 combinatorics, dp 3,244 1m 52s ✓ D Numbers 2000 constructive-algorithms, implementation 1,261 1m 38s ✓ E Birthday 2900 geometry,...

Practice › Codeforces Solutions ›

Unknown Language Round 3

Unknown Language Round 3 Special | 10 problems | 10/10 verified | Difficulty 1100-2400 | 23m 31s # Problem Rating Tags Accepted Time ✓ A Carpeting the Room 1100 *special, implementation 1,025 2m 19s ✓ B Friendly Numbers 1500 *special, implementation 581 2m 19s ✓ C A+B 1400 *special, implementation 625 1m 27s ✓ D World of Mouth 1500 *special, strings 365 2m 18s ✓ E Lamps in a Line...

Practice › Codeforces Solutions ›

Codeforces Beta Round 83 (Div. 1 Only)

Codeforces Beta Round 83 (Div. 1 Only) Div. 1 | 5 problems | 5/5 verified | Difficulty 1400-2700 | 11m 41s # Problem Rating Tags Accepted Time ✓ A Dorm Water Supply 1400 dfs-and-similar, graphs 5,905 2m 19s ✓ B Basketball Team 1600 combinatorics, dp, math 4,272 2m 22s ✓ C Arrangement 2400 bitmasks, dp 460 2m 35s ✓ D Crime Management 2400 dp, graphs, matrices 487 2m 6s ✓...

Practice › Codeforces Solutions ›

Codeforces Beta Round 87 (Div. 1 Only)

Codeforces Beta Round 87 (Div. 1 Only) Div. 1 | 5 problems | 3/5 verified | Difficulty 900-2600 | 11m 15s # Problem Rating Tags Accepted Time ✓ A Party 900 dfs-and-similar, graphs, trees 43,322 1m 51s ✓ B Lawnmower 1500 greedy, sortings 2,840 1m 30s ✓ C Plumber 2200 math 676 2m 56s D Unambiguous Arithmetic Expression 2600 dp, expression-parsing 454 2m 6s ✓ E Linear Kingdom Races 2400...

Practice › Codeforces Solutions ›

Codeforces Beta Round 88

Codeforces Beta Round 88 Beta | 5 problems | 5/5 verified | Difficulty 1300-2900 | 13m 35s # Problem Rating Tags Accepted Time ✓ A Elevator 1300 implementation, math 2,225 2m 31s ✓ B Very Interesting Game 1800 brute-force, number-theory 1,743 2m 31s ✓ C Cycle 2000 dfs-and-similar, graphs 2,962 3m ✓ D Not Quick Transformation 2500 divide-and-conquer, math 369 2m 20s ✓ E Tree or not Tree 2900 data-structures,...

Practice › Codeforces Solutions ›

Codeforces Beta Round 80 (Div. 1 Only)

Codeforces Beta Round 80 (Div. 1 Only) Div. 1 | 5 problems | 3/5 verified | Difficulty 1100-2900 | 10m 20s # Problem Rating Tags Accepted Time ✓ A Testing Pants for Sadness 1100 greedy, implementation, math 6,572 1m 39s ✓ B Cthulhu 1500 dfs-and-similar, dsu, graphs 10,648 1m 43s ✓ C Russian Roulette 1900 constructive-algorithms, greedy 1,049 2m ✓ D Time to Raid Cowavans 2100 brute-force, data-structures, sortings 2,526...

#dfs-and-similar

CF 1558E - Down Below

CF 1552D - Array Differentiation

CF 1552I - Organizing a Music Festival

CF 1389G - Directing Edges

CF 1385E - Directing Edges

CF 1385G - Columns Swaps

CF 1367E - Necklace Assembly

CF 1307F - Cow and Vacation

CF 1266F - Almost Same Distance

CF 1250N - Wires

CF 1242C - Sum Balance

Codeforces Round 449 (Div. 1)

CF 896A - Nephren gives a riddle

Codeforces Round 468 (Div. 1, based on Technocup 2018 Final Round)

CF 930A - Peculiar apple-tree

Codeforces Round 467 (Div. 1)

CF 936B - Sleepy Game

CF 948A - Protect Sheep

Codeforces Round 470 (rated, Div. 2, based on VK Cup 2018 Round 1)

Codeforces Round 469 (Div. 1)

CF 949C - Data Center Maintenance

Helvetic Coding Contest 2018 online mirror (teams allowed, unrated)

CF 958B2 - Maximum Control (medium)

Divide by Zero 2018 and Codeforces Round 474 (Div. 1 + Div. 2, combined)

CF 960E - Alternating Tree

Educational Codeforces Round 42 (Rated for Div. 2)

CF 962F - Simple Cycles Edges

Tinkoff Internship Warmup Round 2018 and Codeforces Round 475 (Div. 1)

CF 963B - Destruction of a Tree

Codeforces Round 479 (Div. 3)

CF 977D - Divide by three, multiply by two

Codeforces Round 482 (Div. 2)

CF 979C - Kuro and Walking Route

Codeforces Round 484 (Div. 2)

CF 982C - Cut 'em all!

Codeforces Round 490 (Div. 3)

CF 999E - Reachability from the Capital

CF 1005F - Berland and the Shortest Paths

CF 1006E - Military Problem

Codeforces Round 499 (Div. 1)

CF 1010D - Mars rover

Codeforces Round 500 (Div. 1) [based on EJOI]

CF 1012B - Chemical table

CF 1016F - Road Projects

Codeforces Round 503 (by SIS, Div. 2)

CF 1020B - Badge

CF 1023F - Mobile Phone Network

CF 1027F - Session in BSU

Educational Codeforces Round 49 (Rated for Div. 2)

CF 1027D - Mouse Hunt

Lyft Level 5 Challenge 2018 - Elimination Round

CF 1033A - King Escape

CF 1036G - Sources and Sinks

Manthan, Codefest 18 (rated, Div. 1 + Div. 2)

CF 1037D - Valid BFS?

CF 1038E - Maximum Matching

Codeforces Round 660 (Div. 2)

Baltic Olympiad in Informatics 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated)

CF 1039C - Network Safety

Lyft Level 5 Challenge 2018 - Final Round

CF 1044B - Intersecting Subtrees

Bubble Cup 11 - Finals [Online Mirror, Div. 1]

CF 1045C - Hyperspace Highways

CF 1560F2 - Nearest Beautiful Number (hard version)

CF 1559D2 - Mocha and Diana (Hard Version)

CF 1553E - Permutation Shift

CF 1388D - Captain Flint and Treasure

CF 1387B2 - Village (Maximum)

CF 1387A - Graph

CF 1379C - Choosing flowers

CF 1370F2 - The Hidden Pair (Hard Version)

CF 1369F - BareLee

CF 1363E - Tree Shuffling

CF 1361C - Johnny and Megan's Necklace

Codeforces Round 640 (Div. 4)

CF 1344C - Quantifier Question

CF 1340C - Nastya and Unexpected Guest

CF 1338D - Nested Rubber Bands

CF 1335F - Robots on a Grid