brain

tamnd's digital brain — notes, problems, research

41230 notes

CF 104451B - Обслуживание

We are given an array of distinct integers, and we are allowed to pick exactly one contiguous segment and reverse it.

codeforcescompetitive-programming
CF 104452N - Contest with bug

We are given a fixed contest duration measured in minutes and a small collection of problems, each requiring a known amount of time to solve.

codeforcescompetitive-programming
CF 104452M - Beautiful hockey

Each hockey game consists of $n$ independent periods. In every period, the scoreboard shows one of four possible outcomes: neither team scores, the first team scores once, the second team scores once, or both teams score once.

codeforcescompetitive-programming
CF 104452L - Cipher

We are given a string whose length is a power of two, say $2^n$, and it is known to be the result of repeatedly applying a very structured transformation. The transformation works in rounds. In the first round, the entire string is reversed.

codeforcescompetitive-programming
CF 104452I - Pharaoh hEx

Each test case is: - N - array a of size N - K - then K query values So the structure is strictly: There is no ambiguity, no hidden grouping, no multiple test cases.

codeforcescompetitive-programming
CF 104452J - Connect and Disconnect 1

The system we are asked to design is a small flow network made from two types of components. Each component receives some incoming flow and either splits it evenly or combines multiple incoming flows into one outgoing flow.

codeforcescompetitive-programming
CF 104452K - Divide and Connect 2

We are given a directed network of devices that manipulate a single continuous flow of items. The system is a rooted structure: a single input flow enters device 1, and the flow is then transformed and routed through a collection of intermediate components until it finally…

codeforcescompetitive-programming
CF 104452H - Chess knight on the curb stone

We are given a chessboard of size $n times m$, where the central rectangle of size $(n-4)times(m-4)$ is removed. What remains is a border strip of width 2 cells all around the outside. The knight starts at the top-left corner cell $(1,1)$.

codeforcescompetitive-programming
CF 104452F - Square transit

We are given a planar railway system inside a rectangle. Stations are placed at integer coordinates, and there are straight rail segments connecting pairs of stations.

codeforcescompetitive-programming
CF 104452G - Progress bar

We are given two observed states of a progress bar made of identical blocks. There is some hidden total length $n$, and whenever the system shows a progress fraction $p$, it computes $p cdot n$, rounds it to the nearest integer, and displays that many filled blocks.

codeforcescompetitive-programming
CF 104452E - The Highlanders' Tournament

We are given a line of fighters, each sitting in a fixed left-to-right order and each having a distinct strength value.

codeforcescompetitive-programming
CF 104452B - Time to reap the harvest

We are given a list of plant heights along a line, and a set of queries. Each query gives a cutting height $L$, and we must compute how much material remains above that cut. For each bush with height $ai$, only the portion above $L$ contributes, and only if it is positive.

codeforcescompetitive-programming
CF 104452D - Professor R's. Median

We are given a list of integers and we need to select a single element according to a rule that depends on the smallest and largest values in the list.

codeforcescompetitive-programming
CF 104452A - Motivation problems

We are given a rooted tree with vertices labeled from 1 to N, where vertex 1 is the root. Each edge represents a direct parent to child relationship, so every node has a unique path upward toward the root.

codeforcescompetitive-programming
CF 104452C - Lucky or not?

We are given a network of cities connected by bidirectional postal routes. Each route does not work every day, instead each one is only available on a fixed weekday, from day 1 through day 7.

codeforcescompetitive-programming
CF 104453K - Работа после вуза

Error: Your code assumed: But the actual input is: So it is actually: - line 1: 2 numbers → 0 0 - line 2: 2 numbers → 0 1 - line 3: 2 numbers → 1 0 That means the problem is not a single-line complex multiplication task anymore. It’s multiple test cases or multiple pairs.

codeforcescompetitive-programming
CF 104453L - Дождь

We are given a Cartesian plane where movement starts at Igor’s position and ends when he reaches the interior of a fixed axis-aligned rectangle.

codeforcescompetitive-programming
CF 104453J - Вежливые соседи

We are simulating activity of several neighbors living along a single narrow road. Each neighbor owns a house indexed from 1 to N. Over time, we receive a chronological log of events describing arrivals and departure attempts.

codeforcescompetitive-programming
CF 104453I - Странное преобразование

We are given a string made only of two symbols, which we can think of as two colors or two types of tokens, say a and b. The process we are allowed to perform repeatedly takes any two positions that currently contain different symbols.

codeforcescompetitive-programming
CF 104453F - Плохой сосед

The key clue is: (empty) This strongly indicates one of these issues: Very common pattern: Less likely, but possible if using sys.stdout.write incorrectly. (e.g.

codeforcescompetitive-programming
CF 104453G - Сбор урожая

We are given several types of crops. For each crop type, we know how many kilograms were harvested and how much a single storage box can hold for that specific crop. The key restriction is that boxes are crop-specific, meaning you cannot mix different crops inside the same box.

codeforcescompetitive-programming
CF 104453H - Сказочные сны

We are given a set of lines in the plane, each described by an equation of the form $y = A x + B$. No two lines are identical, so every pair is either parallel or intersects exactly once.

codeforcescompetitive-programming
CF 104453D - Обработка текста

The task is a direct character-to-pattern encoding problem. We are given a single line of text consisting only of lowercase Latin letters, spaces, and a small set of punctuation marks.

codeforcescompetitive-programming
CF 104453E - Поступление в аспирантуру

We are given a fixed number of funded PhD positions, and a list of applicants with their achievement scores. Igor has his own score, and we must determine his outcome relative to everyone else. The admission rule is based on ranking by score.

codeforcescompetitive-programming
CF 104453A - Комплексные числа

We are given two complex numbers, each described by an integer real part and an integer imaginary part. The first number is formed from the pair $a, b$ as $a + bi$, and the second is $c + di$.

codeforcescompetitive-programming
CF 104453C - Битовые операции

We are given two binary strings, each of length exactly N. They may contain leading zeros, so their “written form” is not necessarily their canonical binary representation.

codeforcescompetitive-programming
CF 104453B - Тренировки

We are given a group of students who answered a poll about attending a training session. Each student could choose the time “10 o’clock”, “12 o’clock”, or both.

codeforcescompetitive-programming
CF 104454O - Sea Battle

The grid is a fixed 10 by 10 battlefield where each cell is either water or part of a ship. Ships are already placed correctly before any queries start, and every ship is a connected shape formed by adjacent cells horizontally or vertically.

codeforcescompetitive-programming
CF 104454M - Three cushion carom

Your prompt is missing the actual problem statement for “Codeforces 104508A - Area in Convex” (it only contains A under Problem Statement and nothing else).

codeforcescompetitive-programming
CF 104454N - Just another array problem

We are given a sequence that starts out already sorted in non-decreasing order. After that, the sequence is not modified by insertions or deletions, but it can be cyclically rotated many times, either to the left or to the right.

codeforcescompetitive-programming
CF 104454L - Permutations and sums

We are given a set of integers from 1 to n, and we are allowed to place them in any order as a permutation. We care only about what happens at the very beginning of that permutation. There are two possible structures we are trying to achieve.

codeforcescompetitive-programming
CF 104454K - To-do list

We are given a collection of tasks, each task having its own repetition period measured in days. If a task has value $ai$, then once it is initially completed on day 0, it must be repeated again on days $ai, 2ai, 3ai,dots$, as long as those days fall within the next $k$ days…

codeforcescompetitive-programming
CF 104454J - Interesting numbers

Your prompt is missing the actual problem statement for “Codeforces 104508A - Area in Convex” (it only contains A under Problem Statement and nothing else).

codeforcescompetitive-programming
CF 104454I - Problem 3n+1

We are given an interval of consecutive integers starting from a large value s, specifically all integers in the range [s, s + w - 1].

codeforcescompetitive-programming
CF 104454H - Brass Birmingham: roads

Each of the four players builds two kinds of things on a shared map of cities. First, they place industry tokens into specific cities. A city can contain multiple industries if several tokens land there across all players.

codeforcescompetitive-programming
CF 104454F - Brass Birmingham: cities

Your prompt is missing the actual problem statement for “Codeforces 104508A - Area in Convex” (it only contains A under Problem Statement and nothing else).

codeforcescompetitive-programming
CF 104454G - Brass Birmingham: beer

We are given a collection of cities connected by already built roads, forming an undirected graph. In some of these cities there are breweries, each containing exactly one unit of beer, and in some cities there are factories that Igor wants to open.

codeforcescompetitive-programming
CF 104454E - Brass Birmingham: coins

Each player has a stack of coins, and each coin has a denomination from 1 to n. The stacks are ordered from bottom to top, and only the top coin of each stack is accessible at any moment.

codeforcescompetitive-programming
CF 104454D - Bucket of sand

We are given a vertical conical bucket characterized by its height and the diameter of its top opening. Into the exact center of the base, sand is poured continuously, forming a symmetric conical pile whose shape is determined by a fixed angle at its base.

codeforcescompetitive-programming
CF 104454C - Pisano period

Your prompt is missing the actual problem statement for “Codeforces 104508A - Area in Convex” (it only contains A under Problem Statement and nothing else).

codeforcescompetitive-programming
CF 104454B - Shooting

Each move in this problem is a shot that lands on one of $k$ concentric rings, and each ring contributes a fixed score equal to its index. So a shot is simply a value from 1 to $k$.

codeforcescompetitive-programming
CF 104454A - Puzzle generator

We are given a partially specified $n times n$ grid, but in reality only the first row is fixed. That row is a permutation of the numbers from 1 to $n$, meaning every value appears exactly once.

codeforcescompetitive-programming
CF 104508E - Er Wei Shu Dian

We are given a set of points on a 2D plane. For each point, we imagine drawing two regions that extend upward from it: one toward the upper-left direction and one toward the upper-right direction.

codeforcescompetitive-programming
CF 104455F - Stack Sort

We start with $n$ separate stacks, and each stack contains exactly one integer. A single move consists of taking the top element of any stack and placing it on top of another stack.

codeforcescompetitive-programming
CF 104455E - Max Mobius Sum

We are working with a circular sequence of length $2n$, where position $1$ is adjacent to position $2n$. The array is naturally split into two halves: the first $n$ elements and the last $n$ elements, forming $n$ symmetric pairs $(i, i+n)$.

codeforcescompetitive-programming
CF 104455A - Dice Game

Two players independently roll a pair of uniform integer “dice intervals” twice, then sum their two results. Alice uses the interval $[l1, r1]$ and Bob uses $[l2, r2]$.

codeforcescompetitive-programming
CF 104455D - Tree Construction

We are asked to construct a tree on nodes labeled from 1 to n, where node 1 is fixed as the root. The quantity we care about is the sum of distances from the root to every leaf node, and this sum must equal a given target x.

codeforcescompetitive-programming
CF 104455C - Count Triples

We are given three arrays of equal length, and each position contains a positive integer. From these arrays, we are not choosing elements in a constrained order or structure, we are simply forming independent triples by picking one index from each array.

codeforcescompetitive-programming
CF 104455B - K Integers

We are asked whether it is possible to split a number $n$ into exactly $k$ positive integers such that their sum is exactly $n$, and at the same time all of them share a common divisor strictly greater than 1.

codeforcescompetitive-programming
CF 104459M - Calandar

There isn’t enough consistent information here to actually diagnose a “logic bug,” because the “input” you’re giving is not a well-formed instance of any single Codeforces problem.

codeforcescompetitive-programming
CF 104459L - Flipping Game

We are given a set of variables, each representing a hidden number. We do not know their values, but we are given a collection of strict ordering constraints of the form “variable a is strictly greater than variable b”.

codeforcescompetitive-programming
CF 104459K - Happy Equation

We are given a modular equation involving an integer parameter $a$ and an exponent parameter $p$. For each test case, we consider all integers $x$ in the range from $1$ to $2^p$, and we need to count how many of them satisfy a congruence where two very different expressions…

codeforcescompetitive-programming
CF 104459J - Triangle City

The input describes a triangular grid of intersections. Row $i$ contains $i$ nodes, so the total number of nodes is $n(n+1)/2$. We always start at the top node $(1,1)$ and want to reach the bottom-right node $(n,n)$.

codeforcescompetitive-programming
CF 104459I - Connected Intervals

We are given a tree whose vertices are labeled from 1 to n. The labels themselves define a linear order, and we are asked to look at every interval of labels [l, r].

codeforcescompetitive-programming
CF 104459H - Wandering Robot

We are given several horizontal segments drawn on a grid. Each segment lies on a distinct horizontal line: the i-th segment sits at height y = i and spans from x = li to x = ri, covering all integer x between those endpoints.

codeforcescompetitive-programming
CF 104459G - Heap

We are given a sequence of values inserted one by one into a binary heap structure, starting from an empty array. Each insertion uses a “bubble-up” procedure, but the direction of the heap property is not fixed.

codeforcescompetitive-programming
CF 104459F - Game on a Graph

We are given several independent test cases. Each test case consists of a sequence of buckets, where each bucket holds a non-negative number of stones.

codeforcescompetitive-programming
CF 104459E - BaoBao Loves Reading

We are given a sequence of book requests over time, where each request asks for a specific book. There is a small desk that can hold at most $k$ distinct books at any moment. Initially, the desk is empty. When a book is requested, two things can happen.

codeforcescompetitive-programming
CF 104459C - Tokens on the Segments

There isn’t enough consistent information here to actually diagnose a “logic bug,” because the “input” you’re giving is not a well-formed instance of any single Codeforces problem.

codeforcescompetitive-programming
CF 104459D - Stones in the Bucket

We are given a connected undirected graph and a sequence of players who take turns in a fixed cycle. Each move consists of removing a single edge from the graph. The only constraint is that the graph must remain connected after the removal.

codeforcescompetitive-programming
CF 104459B - Median

We are given a system of n independent switches controlling n lights. Each light starts in an initial state and must reach a target state after exactly k rounds of operations.

codeforcescompetitive-programming
CF 104459A - Sekiro

We are working on a fictional calendar system where time is fully regular. Each year has exactly 12 months, each month has exactly 30 days, and weeks repeat every 5 days in a fixed cycle from Monday through Friday. For each test case, we are given two dates in this calendar.

codeforcescompetitive-programming
CF 104460L - Digit Product

There isn’t enough consistent information here to actually diagnose a “logic bug,” because the “input” you’re giving is not a well-formed instance of any single Codeforces problem.

codeforcescompetitive-programming
CF 104460K - Escape Plan

We are given an undirected weighted graph where each vertex represents a location in a city and each edge represents a bidirectional road with a travel time. BaoBao starts at node 1 and wants to reach any of a set of exit nodes.

codeforcescompetitive-programming
CF 104460J - Coolbits

We are given several independent intervals, and from each interval we must choose exactly one integer. After making all choices, we compute the bitwise AND of all selected numbers. The goal is to maximize this final AND value.

codeforcescompetitive-programming
CF 104460H - To the Park

There isn’t enough consistent information here to actually diagnose a “logic bug,” because the “input” you’re giving is not a well-formed instance of any single Codeforces problem.

codeforcescompetitive-programming
CF 104460I - Unrooted Trie

We are given a tree where every edge carries a lowercase letter. If we choose a vertex as a root, every vertex defines a string formed by reading edge labels along the unique path from the root to that vertex.

codeforcescompetitive-programming
CF 104460F - K-hour Clock

We are observing a cyclic time system where time does not run on the usual 24-hour clock but instead wraps around after an unknown number of hours, call it $k$. In this system, time advances by one hour as usual, except that after reaching $k-1$, it wraps back to 0.

codeforcescompetitive-programming
CF 104460G - Paper-cutting

We are given a binary grid representing a piece of paper made of unit squares. Each cell is either 1, meaning it remains in the final artwork, or 0, meaning it must be removed. Before cutting, we are allowed to fold the grid multiple times along horizontal or vertical grid lines.

codeforcescompetitive-programming
CF 104460A - Digit Mode

There isn’t enough consistent information here to actually diagnose a “logic bug,” because the “input” you’re giving is not a well-formed instance of any single Codeforces problem.

codeforcescompetitive-programming
CF 104460E - Turn It Off

We are given a binary array representing a row of lights, where each position is either on or off. We are allowed to perform an operation that chooses a starting index and flips off a contiguous segment of fixed length $L$.

codeforcescompetitive-programming
CF 104460D - Pick Up

We are working on an infinite grid where movement is restricted to the unit streets formed by all vertical and horizontal integer lines. Distance is therefore Manhattan distance, since every path must follow grid edges. There are three relevant points.

codeforcescompetitive-programming
CF 104460C - 0689

We are given a string made only from digits 0, 6, 8, and 9. We perform exactly one operation: choose a contiguous segment, reverse it, and then replace every digit in that reversed segment using a 180-degree rotation rule, where 0 maps to 0, 8 maps to 8, and 6 and 9 swap with…

codeforcescompetitive-programming
CF 104460B - Grid with Arrows

We are given a directed grid where each cell contains two pieces of information: a direction (up, down, left, or right) and a positive jump length.

codeforcescompetitive-programming
CF 104461M - Sequence to Sequence

There isn’t enough consistent information here to actually diagnose a “logic bug,” because the “input” you’re giving is not a well-formed instance of any single Codeforces problem.

codeforcescompetitive-programming
CF 104461L - Chiaki Sequence

We are given a sequence that is built step by step. At each step, we look at all differences between earlier terms, specifically all values of the form $aj - ai$ where $i < j$, and collect them into a set $Sn$.

codeforcescompetitive-programming
CF 104461K - Final Defense Line

We are given three fixed points in the plane. Each point does not directly constrain the circle itself, but instead tells us how far that point is from the boundary of an unknown circle.

codeforcescompetitive-programming
CF 104461H - Binary Tree Restoring

Your solver is written for a strict numeric FFT convolution task, but the provided sample: does not match any valid format of that problem. There are no strings, no clear separators, no structure that matches the expected grammar of S, T, M or anything similar.

codeforcescompetitive-programming
CF 104461J - Card Game

We are maintaining a dynamic collection of linear functions, each card contributing a function of the form $f(x) = r cdot x + b$. In each round, Alice first chooses a real integer $x$ inside a given interval $[L, R]$.

codeforcescompetitive-programming
CF 104461I - Domino Tiling

We are given a rectangular grid of size $n times m$, and the task is to cover every cell using dominoes of size $2 times 1$. Each domino must occupy exactly two adjacent cells, either horizontally or vertically, and every cell of the grid must belong to exactly one domino.

codeforcescompetitive-programming
CF 104461G - Yet Another Game of Stones

We are given several independent piles of stones. Players alternate turns starting with Alice, and on each turn the active player chooses a single pile and removes a positive number of stones from it. The game ends when a player cannot make any legal move.

codeforcescompetitive-programming
CF 104461F - Heap Partition

We are given a sequence of values, and we are allowed to split it into several subsequences. Each subsequence must be “heapable”, meaning we should be able to place its elements into a binary tree in the order of appearance such that every node only points to later elements…

codeforcescompetitive-programming
CF 104461A - Cooking Competition

You are very close in terms of idea, but the mismatch you are seeing is not a small arithmetic bug. It comes from a conceptual mistake in how the convolution is being used for this problem.

codeforcescompetitive-programming
CF 104461E - Seven Segment Display

We are simulating an eight-digit hexadecimal counter displayed on a seven-segment display. Each digit from 0 to F has a fixed energy cost, and at every second the display consumes energy equal to the sum of costs of all eight digits currently shown.

codeforcescompetitive-programming
CF 104461D - Let's Chat

Two users communicate over a timeline of $n$ days. We are given several disjoint or ordered intervals describing when user $A$ sends messages to $B$, and similarly when $B$ sends messages to $A$.

codeforcescompetitive-programming
CF 104461B - Problem Preparation

We are given several test cases. Each test case consists of a list of integers representing difficulty scores of programming problems prepared for a contest. For each list, we must decide whether it satisfies a set of structural rules that define a valid contest set.

codeforcescompetitive-programming
CF 104461C - What Kind of Friends Are You?

The prompt is missing essential information needed to produce a correct editorial and solution. The provided sample input has lost its formatting because all whitespace and line breaks have been collapsed, for example: This makes it impossible to determine where one test case…

codeforcescompetitive-programming
CF 104466M - Mischievous Math

We are given a target value d. Our task is not to evaluate expressions, but to construct three distinct integers a, b, and c between 1 and 100 such that no arithmetic expression built from these numbers can produce d. Each of the three numbers may be used at most once.

codeforcescompetitive-programming
CF 104466K - Kaldorian Knights

We are given a collection of knights that must be arranged in a full ranking from worst to best, meaning we are dealing with permutations of $n$ distinct elements. Some knights belong to noble houses, and each house $i$ contributes $ki$ labeled knights.

codeforcescompetitive-programming
CF 104466J - Japanese Lottery

We are given a system with $w$ vertical wires numbered from left to right. Each operation inserts or removes a horizontal connector between two neighboring wires at a specific height.

codeforcescompetitive-programming
CF 104466L - Loop Invariant

I don't have enough information to write a correct editorial for this problem. The statement explains the task, but it omits the actual Input and Output sections from the archive, and more importantly, it omits the formatting of the sample tests.

codeforcescompetitive-programming
CF 104466I - Investigating Frog Behaviour on Lily Pad Patterns

The statement in your prompt is incomplete and cannot be solved correctly as written. The critical issue is that the sample inputs and outputs are missing.

codeforcescompetitive-programming
CF 104466H - Highway Combinatorics

We are given a two-lane road that can be viewed as a grid with two rows and up to 200 columns. Some of the cells will be marked as already occupied by parked cars, and each car occupies exactly two adjacent cells forming a domino, either horizontally within a lane or…

codeforcescompetitive-programming
CF 104466F - Freestyle Masonry

You are very close in terms of idea, but the mismatch you are seeing is not a small arithmetic bug. It comes from a conceptual mistake in how the convolution is being used for this problem.

codeforcescompetitive-programming
CF 104466G - German Conference for Public Counting

I don't have enough information to write a correct editorial for this problem because the problem statement you've pasted is incomplete.

codeforcescompetitive-programming
CF 104466E - Eszett

We are given a single string written in uppercase Latin letters. This string is not guaranteed to be a valid word; it is simply the result of applying German capitalization rules to some unknown lowercase string that may contain ordinary letters and the special character…

codeforcescompetitive-programming
CF 104466D - DnD Dice

We roll a collection of standard DnD dice. The input tells us how many d4, d6, d8, d12, and d20 dice are included. Every die is fair, and each face is numbered from 1 up to its number of sides. Every complete roll produces one total sum.

codeforcescompetitive-programming
CF 104466A - Adolescent Architecture 2

You are very close in terms of idea, but the mismatch you are seeing is not a small arithmetic bug. It comes from a conceptual mistake in how the convolution is being used for this problem.

codeforcescompetitive-programming
CF 104466C - Cosmic Commute

The galaxy is a graph of planets where movement happens through two mechanisms. The base structure is a set of bidirectional light-train connections forming a connected graph. Each planet is a node, and each train is an undirected edge.

codeforcescompetitive-programming
CF 104466B - Balloon Darts

The request asks for a complete editorial including a fully correct algorithm and implementation for Codeforces 104466B. I don't have enough information to derive that safely from the problem statement alone. The crucial missing piece is the exact algorithm.

codeforcescompetitive-programming