#two pointers

CF 939C - Convenient For Everybody Rating: 1600 Tags: binary search, two pointers Model: gpt-5-3-mini Solve time: 1m 29s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a339882-e2e8-83ec-ad7b-d55e1e16e616 Solution Problem Understanding We are given a circular timeline with $n$ discrete hours, where hour labels wrap around so that after $n$ comes 1 again. Each of the $n$ timezones shifts local time by exactly one hour relative to its neighbor, so a global start...

CF 965D - Single-use Stones Rating: 1900 Tags: binary search, flows, greedy, two pointers Model: gpt-5-3-mini Solve time: 1m 25s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a33a3ef-c198-83ec-ab18-235bfb734e32 Solution Problem Understanding We are given a river of width $w$. Along the river, at each integer position $i$ from $1$ to $w-1$, there are $a_i$ stones initially placed at that distance from the starting bank. A frog starts at the left bank (position...

CF 1041D - Glider Rating: 1700 Tags: binary search, data structures, two pointers Model: gpt-5-3-mini Solve time: 1m 35s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a337e1b-8584-83ec-825a-6d7235a7a6fb Solution Problem Understanding A glider is released from a moving airplane at some integer x-coordinate while the plane is fixed at height h. Once released, the glider always moves one unit to the right per second. At the same time, its height decreases by one...

CF 958F2 - Lightsabers (medium) Rating: 1800 Tags: binary search, two pointers Model: gpt-5-3-mini Solve time: 2m 35s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a339f05-474c-83ec-8348-d5aef0244721 Solution Problem Understanding We are given a line of Jedi, each Jedi wearing a lightsaber of one of several colors. We are also given a target requirement: for every color, we want to see a fixed number of knights of that color. The goal is not...

CF 1042D - Petya and Array Rating: 1800 Tags: data structures, divide and conquer, two pointers Model: gpt-5-3-mini Solve time: 1m 19s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a337e74-0c8c-83ec-89c6-71e8972be404 Solution Problem Understanding We are given a sequence of integers laid out in a row, and we are interested in contiguous fragments of this row. For every possible fragment, we compute its sum, and we need to count how many of these...

CF 954G - Castle Defense Rating: 2000 Tags: binary search, data structures, greedy, two pointers Model: gpt-5-3-mini Solve time: 1m 46s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a327d26-ccf4-83ec-bcbf-87461eeed768 Solution Problem Understanding Each position on the wall can be thought of as a segment that needs protection strength. You are given an initial arrangement of archers, and each archer does not only defend its own position but also helps nearby positions within...

CF 924B - Three-level Laser Rating: 1600 Tags: binary search, greedy, two pointers Model: gpt-5-3-mini Solve time: 1m 25s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a326e6b-2cbc-83ec-b7fb-a28cecb0a5b4 Solution Problem Understanding We are given a strictly increasing array of energy levels. We must pick three indices $i < j < k$ and interpret them as a three-step physical process that produces a ratio between useful energy and spent energy. The process depends only...

CF 1036D - Vasya and Arrays Rating: 1600 Tags: greedy, two pointers Model: gpt-5-3-mini Solve time: 1m 15s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a32a1e8-5644-83ec-ad41-fedccd51e290 Solution Problem Understanding We are given two sequences of positive integers. We are allowed to repeatedly compress any contiguous block into a single number equal to the sum of that block. After doing these compressions independently on both arrays, we want the resulting arrays to become...

CF 899E - Segments Removal Rating: 2000 Tags: data structures, dsu, flows, implementation, two pointers Model: gpt-5-5 Solve time: 1m 28s Verified: yes (1/1 samples) Solution Problem Understanding The array starts as a sequence of integers, and it evolves through a very specific greedy deletion rule. At any moment you look at all maximal blocks of consecutive equal values, pick the block with the largest length, and if several blocks...

CF 961B - Lecture Sleep Rating: 1200 Tags: data structures, dp, implementation, two pointers Model: gpt-5-3-mini Solve time: 1m 14s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a3280b1-1f98-83ec-b0ee-5785d1836f05 Solution Problem Understanding The lecture is a sequence of minutes, and during each minute the lecturer produces a certain number of theorems. If Mishka is awake at that minute, those theorems are recorded; if he is asleep, they are lost. The twist is that...

CF 1282C - Petya and Exam Rating: 1800 Tags: greedy, sortings, two pointers Model: gpt-5-3-mini Solve time: 2m 55s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a2da601-1174-83ec-845c-92c2dc74892b Solution Problem Understanding Each test case describes an exam where problems arrive with deadlines and take different amounts of time depending on whether they are easy or hard. Petya processes problems sequentially starting from time zero, choosing an order, and may stop at any integer...

CF 1343D - Constant Palindrome Sum Rating: 1700 Tags: brute force, data structures, greedy, two pointers Model: gpt-5-3-mini Solve time: 4m 46s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e1e83-bbf8-83ec-8cb1-8f509740ced4 Solution Problem Understanding We are given an array of even length, and we look at it as a set of mirrored pairs: the first element is paired with the last, the second with the second last, and so on. For each such...

CF 1369C - RationalLee Rating: 1400 Tags: greedy, math, sortings, two pointers Model: gpt-5-5 Solve time: 2m 35s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e511f-c224-83ec-b707-723e5d51dfb6 Solution Problem Understanding We are given a collection of integers that must be split into groups, where each group is assigned to a different friend. Each friend receives exactly a fixed number of integers, and every integer must be used exactly once. The satisfaction of a...

CF 1355C - Count Triangles Rating: 1800 Tags: binary search, implementation, math, two pointers Model: gpt-5-5 Solve time: 4m 30s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e337e-c354-83ec-b9bf-1c6c92a28cf3 Solution Problem Understanding We are given four integers $A \le B \le C \le D$. From these bounds we must choose three integers $x, y, z$ such that each side comes from a different interval: $x$ is chosen from $[A, B]$, $y$ from $[B,...

CF 1313E - Concatenation with intersection Rating: 2700 Tags: data structures, hashing, strings, two pointers Model: gpt-5-3-mini Solve time: 3m 20s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2de325-48b4-83ec-b5e4-21871b1e6570 Solution Problem Understanding We are given two strings of equal length, call them the first and second source strings, and a target string. We are allowed to pick any contiguous segment from the first string and any contiguous segment from the second string,...

CF 1380D - Berserk And Fireball Rating: 2000 Tags: constructive algorithms, greedy, implementation, math, two pointers Model: gpt-5-3-mini Solve time: 3m 18s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e6837-7194-83ec-8eb1-70496101292f Solution Problem Understanding We are given a sequence of distinct integers representing warriors arranged in a line. We are also given a target sequence, also consisting of distinct integers. The goal is to transform the initial line into the target line using...

CF 1379D - New Passenger Trams Rating: 2300 Tags: binary search, brute force, data structures, sortings, two pointers Model: gpt-5-3-mini Solve time: 4m 36s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a2e6460-6b3c-83ec-8292-9e3f9f8e4c60 Solution Problem Understanding We are given a full-day timetable where freight trains already depart at fixed times. The day is cyclic with h hours and m minutes per hour, so every train time can be treated as a point on...

CF 1381C - Mastermind Rating: 2500 Tags: constructive algorithms, graph matchings, greedy, implementation, sortings, two pointers Model: gpt-5-3-mini Solve time: 4m 37s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a2e6d9f-55a8-83ec-97be-24bac196aec3 Solution Problem Understanding We are given a sequence b of length n , representing Bob’s guess, and two integers x and y describing how this guess overlaps with an unknown hidden sequence a of the same length. The hidden sequence uses colors...

CF 1359D - Yet Another Yet Another Task Rating: 2000 Tags: data structures, dp, implementation, two pointers Model: gpt-5-5 Solve time: 4m 32s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e3b68-4258-83ec-a34a-76ee9dcc4897 Solution Problem Understanding We are given an array of integers arranged in a line. Alice first selects any contiguous segment of this array. After that, Bob removes exactly one element from inside that chosen segment. The score is the sum of...

CF 1290B - Irreducible Anagrams Rating: 1800 Tags: binary search, constructive algorithms, data structures, strings, two pointers Model: gpt-5-5 Solve time: 5m 7s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2dbb0a-a9b0-83ec-bfb3-954d543b2b2f Solution Problem Understanding We are given a base string and many queries over its substrings. Each query asks whether the chosen substring admits at least one “irreducible anagram”. To interpret this, imagine we take the substring and consider all possible permutations...

CF 1312F - Attack on Red Kingdom Rating: 2500 Tags: games, two pointers Model: gpt-5-3-mini Solve time: 3m 57s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a2de030-9178-83ec-ba86-efd9bfd613fa Solution Problem Understanding We are given a row of castles, each starting with some number of soldiers. Two players alternate turns, starting with the White King, and each turn consists of choosing a castle and applying one of three attack types that reduce the number...

CF 1333F - Kate and imperfection Rating: 2200 Tags: greedy, implementation, math, number theory, sortings, two pointers Model: gpt-5-3-mini Solve time: 2m 21s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e0a51-1884-83ec-a398-ce3d30119865 Solution Problem Understanding We are given the numbers from 1 to n. We must choose subsets of these numbers and measure how “bad” a subset is. The badness is defined by looking at every pair inside the subset, computing their gcd,...

CF 1374D - Zero Remainder Array Rating: 1400 Tags: math, sortings, two pointers Model: gpt-5-5 Solve time: 1m 42s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e5b90-5328-83ec-aa40-c68158cde90a Solution Problem Understanding We are given an array of positive integers. We can perform a sequence of moves, and each move advances a global counter x starting from zero. At each step we either skip or “use” the current value of x on exactly one...

CF 1342D - Multiple Testcases Rating: 1900 Tags: binary search, constructive algorithms, data structures, greedy, sortings, two pointers Model: gpt-5-3-mini Solve time: 8m 41s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a2e1bc3-6528-83ec-be3b-9d57dd5c8d13 Solution Problem Understanding We are given a collection of arrays, but the actual contents of these arrays do not matter at all. Each array is characterized only by its size. Our task is to pack all these arrays into several...

CF 1335E1 - Three Blocks Palindrome (easy version) Rating: 1700 Tags: binary search, brute force, data structures, dp, two pointers Model: gpt-5-3-mini Solve time: 3m 26s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a2e0ec6-5db8-83ec-a770-f21d2987bf2e Solution Problem Understanding We are given a sequence of integers and asked to extract a subsequence that has a very specific structure. The subsequence must look like a block of repeated value x , followed by a block...

CF 1381D - The Majestic Brown Tree Snake Rating: 3000 Tags: dfs and similar, dp, greedy, trees, two pointers Model: gpt-5-3-mini Solve time: 3m 8s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e6d43-3be8-83ec-91e7-75c0a4fc2a1d Solution Problem Understanding We are given a tree and a “snake” that occupies a simple path between two vertices. The head is at one endpoint of this path and the tail is at the other endpoint. The snake is...

CF 1352E - Special Elements Rating: 1500 Tags: brute force, implementation, two pointers Model: gpt-5-3-mini Solve time: 3m 4s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e2c9c-c2dc-83ec-8a08-1fb9effdb7ac Solution Problem Understanding We are given an array of positive integers, and we want to identify which elements can be “explained” as a sum of a contiguous segment of the array of length at least two. For each value that appears in the array, we...

CF 1252E - Songwriter Rating: 2200 Tags: greedy, two pointers Model: gpt-5-5 Solve time: 3m 36s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2d6d17-3088-83ec-bce9-2fb58380a095 Solution Problem Understanding We are given an original sequence of integers representing a melody. We are not allowed to keep it directly; instead, we must construct a new sequence of the same length that preserves only the “shape” of the original: every step that goes up, stays equal,...

CF 1266D - Decreasing Debts Rating: 2000 Tags: constructive algorithms, data structures, graphs, greedy, implementation, math, two pointers Model: gpt-5-3-mini Solve time: 3m 17s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2d8730-d1b0-83ec-b40b-a8447d19d422 Solution Problem Understanding We are given a directed weighted graph where each vertex represents a person and each directed edge represents a debt from one person to another. The value on an edge is how much money the source person...

CF 1265B - Beautiful Numbers Rating: 1300 Tags: data structures, implementation, math, two pointers Model: gpt-5-3-mini Solve time: 2m 51s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2d863c-a648-83ec-8f8b-4b13830ade05 Solution Problem Understanding We are given a permutation of numbers from 1 to n, and we want to classify each value m from 1 to n as either “good” or “bad”. A value m is considered good if somewhere inside the array there exists...