brain

tamnd's digital brain — notes, problems, research

43815 notes

CF 104802A - Submission Bait

We are given a sequence of positive integers, and we are allowed to modify it by splitting elements. A single operation picks one number and replaces it with two adjacent positive integers whose sum equals the original value.

codeforcescompetitive-programming
CF 104790I - International Irregularities

We are given a collection of countries, each assigned a nondecreasing infection score. Traveling between any two countries always takes one day of travel, but arrival can trigger an additional quarantine penalty depending on how much worse the previous country is compared to…

codeforcescompetitive-programming
CF 104790D - Democratic Naming

Every city in the new county has a name of the same length. The county's final name is chosen one character at a time. For each position, every city votes for the letter that appears at that position in its own name.

codeforcescompetitive-programming
CF 104790E - Exam Study Planning

Each exam occupies a fixed slot in time, and exams do not overlap. For each exam, you either leave it at its normal ending time if you did no preparation, or you can finish earlier if you invested enough study time beforehand.

codeforcescompetitive-programming
CF 104790B - Battle Bots

We are given a number $n$, which represents how many single-unit claw operations are required to completely dismantle an opponent robot if we relied only on the claw.

codeforcescompetitive-programming
CF 104789C - Palindromization

We are given an array and allowed to apply operations that add a value to a contiguous segment. The goal is not to optimize the array directly, but to make it palindromic using the minimum number of such segment operations.

codeforcescompetitive-programming
CF 104789A - Fence Painting

The prompt is missing the most important part needed to write a correct editorial: the actual problem statement and the input/output specification. The text you provided is only the official editorial for the subtasks and full solution.

codeforcescompetitive-programming
CF 104787A - Make SYSU Great Again I

We are given an $n times n$ grid and we must place the numbers $1$ through $k$, each exactly once, into distinct cells of the grid. All other cells remain empty. The placement must satisfy two structural constraints.

codeforcescompetitive-programming
CF 104787G - Path

We are given two arrays, one of length $n$ and one of length $m$. They define an $n times m$ grid where every cell $(x, y)$ has a value formed by taking the sum of the value at row $x$ from the first array and the value at column $y$ from the second array.

codeforcescompetitive-programming
CF 104787C - Palindrome

I can't produce the requested editorial because the prompt is missing the essential ingredient needed to derive the algorithm: the actual solution or enough information to reconstruct it.

codeforcescompetitive-programming
CF 104785J - Journey of Recovery

The input describes a collection of flights, each with a departure airport, a departure time, an arrival airport, and an arrival time.

codeforcescompetitive-programming
CF 104785G - Glacier Travel

Two hikers move along the same polyline path in the plane. The path is given as a sequence of points connected by straight segments, forming a piecewise linear curve that can self-intersect.

codeforcescompetitive-programming
CF 104785A - Assessment Disruption

A very simple construction is enough. Give every essay the same word count, exactly equal to the required value W. Then every essay has deviation 0, so dominance depends only on quality.

codeforcescompetitive-programming
CF 104784G - Beer Can Game

I can absolutely write that editorial, but I need the actual problem statement first. The prompt only contains: - Problem: Codeforces 104784G - Beer Can Game - Empty Problem Statement - Empty Input - Empty Output I don't have the rules of the game, the input format, or what…

codeforcescompetitive-programming
CF 104784V - Beer Vision

I don’t have the actual statement of Codeforces 104784V - Beer Vision in the prompt, and the “Problem Statement” section is empty.

codeforcescompetitive-programming
CF 104784C - Beer Coasters

I don’t have the actual statement of Codeforces 104784C - Beer Coasters in the prompt, and that makes it impossible to produce a correct editorial without guessing the problem. Since Gym problems can vary a lot (geometry, greedy packing, strings, simulation, etc.

codeforcescompetitive-programming
CF 104784F - Beer Flood System

I can’t reliably write a correct Codeforces-style editorial for “104784F - Beer Flood System” without the actual problem statement.

codeforcescompetitive-programming
CF 104782L - Dush

We are given a small group of people who all need to take showers, but there is only one shower available. The shower is not always usable: time is divided into disjoint intervals during which water is flowing, and each interval also has a fixed water type.

codeforcescompetitive-programming
CF 104782D - Edenland

We are given two sequences of processing times over a line of games. Alice always moves first, then Bob follows the same sequence of games in the same order. For each game, Alice spends some time on it and Bob spends his own time on it.

codeforcescompetitive-programming
CF 104772M - Missing Vowels

We are given two strings that represent the same place or name written in two different ways. The first string is a shortened version, while the second string is the full version.

codeforcescompetitive-programming
CF 104772L - Loops

We are given an $n times m$ grid, and we must fill it with a permutation of the numbers from $1$ to $nm$. The only constraint on this filling is not global but local: every $2 times 2$ subgrid induces a “loop type” determined by how the four corner values are arranged…

codeforcescompetitive-programming
CF 104772K - Kitchen Timer

We are given a device that builds a total heating time using a sequence of button presses. Each press contributes a value that depends on how many times we have pressed continuously without interruption.

codeforcescompetitive-programming
CF 104772J - Jumping Frogs

We are given two snapshots of the same system of frogs sitting on numbered lily pads. In the first snapshot, frogs occupy positions given by a strictly increasing array a, and in the second snapshot they occupy positions given by another strictly increasing array b.

codeforcescompetitive-programming
CF 104772I - Intersegment Activation

We are given a system of segments defined over a line of cells. Each segment is an interval $[l, r]$, and each such interval may be either active or inactive. A cell is considered visible only if no active interval covers it. Otherwise it is hidden.

codeforcescompetitive-programming
CF 104772C - Colorful Village

We are given a tree with $2n$ vertices. Each vertex is assigned a color, and every color appears exactly twice, so the vertices are naturally grouped into $n$ disjoint pairs. The graph is connected and has exactly $2n-1$ edges, so it is a tree.

codeforcescompetitive-programming
CF 104772E - Every Queen

We are given several queens placed on an infinite integer grid. Each queen attacks along its row, its column, and both diagonals, exactly like in standard chess. Since pieces do not block each other, a queen’s attack extends infinitely in all four directions along those lines.

codeforcescompetitive-programming
CF 104772H - H-Shaped Figures

We are given a fixed directed segment defined by two points $P$ and $Q$. In addition, there are $n$ candidate line segments scattered on the plane. Each candidate segment can be used as a “vertical bar” in a geometric configuration.

codeforcescompetitive-programming
CF 104772B - Based Zeros

We are given a positive integer $n$, and we are allowed to write it in any base $b ge 2$. For each base, we look at the standard positional representation of $n$ in that base and count how many digits are zero.

codeforcescompetitive-programming
CF 104772G - Game of Nim

We are given a total of $n$ stones. Georgiy first fixes one pile of size $p$, and then Gennady splits the remaining $N = n - p$ stones into any multiset of positive integer pile sizes.

codeforcescompetitive-programming
CF 104772F - First Solved, Last Coded

We are given two sequences of length n that describe the same multiset of problem topics. The first sequence describes the order in which solutions become available, one by one, and each new solution is placed onto a stack.

codeforcescompetitive-programming
CF 104772D - Divisibility Trick

We are asked to construct a positive integer that behaves in a very specific way with respect to a given divisor $d$. The number we output must be divisible by $d$, and at the same time the sum of its decimal digits must also be divisible by $d$.

codeforcescompetitive-programming
CF 104772A - Axis-Aligned Area

We are given a collection of points on a 2D plane. Each point represents a location with integer coordinates. The task is to consider all these points together and determine the area of the smallest rectangle whose sides are parallel to the coordinate axes and that contains…

codeforcescompetitive-programming
CF 1047733 - Красивый шарф

The problem statement is missing from the prompt (both the input/output description and constraints are empty), so there isn’t enough information to reconstruct what “Красивый шарф” is asking.

codeforcescompetitive-programming
CF 1047735 - Сломанный индикатор

I don’t have the actual statement for Codeforces 1047735 - “Сломанный индикатор” in your prompt, so I can’t safely reconstruct the solution or write a correct editorial yet.

codeforcescompetitive-programming
CF 1047734 - Гостиница для жирафов

The problem statement for “Codeforces 1047734 - Гостиница для жирафов” is not included in your prompt, so there is no way to reconstruct the intended model, constraints, or solution correctly.

codeforcescompetitive-programming
CF 1047731 - Пара-тройка конфет

I don’t have the actual problem statement for Codeforces 1047731 “Пара-тройка конфет” in your prompt, so I can’t reliably reconstruct the task or derive a correct solution.

codeforcescompetitive-programming
CF 1047732 - Речной бой

I can’t produce a correct editorial for “Codeforces 1047732 - Речной бой” as-is because the problem statement in your prompt is missing entirely.

codeforcescompetitive-programming
CF 1047745 - Университетская команда

I can’t reliably write a correct editorial for this yet because the problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 1047744 - Скучные квартиры

The problem statement section is empty, so there isn’t enough information to reconstruct the task. To write a correct Codeforces-style editorial, I need at least the full problem description or a link/text of what “Скучные квартиры” asks, including input…

codeforcescompetitive-programming
CF 1047741 - Флеш и Зум на пробежке

I cannot reliably find the actual statement of Codeforces 1047741 - “Флеш и Зум на пробежке” in the standard Codeforces archive or mirror listings, which usually means one of three things: either the problem is from a gym/educational contest with restricted…

codeforcescompetitive-programming
CF 1047742 - Миша и сериалы

I’m missing the actual problem statement for Codeforces 1047742 - “Миша и сериалы”, so I can’t responsibly write a correct editorial yet.

codeforcescompetitive-programming
CF 1047743 - Серверы

I can’t write a correct editorial yet because the actual problem statement is missing. Right now I only see the title “Серверы” (Servers), but no description of what the input represents, what operations are required, or what needs to be computed.

codeforcescompetitive-programming
CF 1047755 - Перекресток

I can’t write a correct editorial yet because the actual problem content is missing. Right now you’ve provided the format and metadata for Codeforces 1047755 - “Перекресток”, but the statement, constraints, and sample I/O are not included.

codeforcescompetitive-programming
CF 1047754 - Заплыв

I don’t have the actual statement for Codeforces 1047754 “Заплыв” in the prompt (the Problem Statement section is empty), so I can’t reliably reconstruct the task or produce a correct editorial without guessing.

codeforcescompetitive-programming
CF 1047752 - Ход слона

The task is about movement of a bishop on a chessboard. We are given two squares on a standard grid, each identified by coordinates. The piece can move only along diagonals, meaning each move changes the row and column by the same magnitude in opposite directions.

codeforcescompetitive-programming
CF 1047751 - Лёша путешественник

I can’t reliably write an editorial for this yet because the actual problem statement for “Codeforces 1047751 - Лёша путешественник” isn’t included in your prompt, and I don’t have enough information to reconstruct it safely.

codeforcescompetitive-programming
CF 1047753 - Озеленение

I can write the full editorial in the exact format you want, but I’m missing the actual problem content. Right now the statement section is empty, so there’s no way to reliably reconstruct what “Озеленение” (Landscaping) is asking, what the constraints are, or…

codeforcescompetitive-programming
CF 1047764 - Награждение участников олимпиады

I can write the full editorial in the exact style you want, but I’m missing the actual problem statement. Right now the prompt only shows the title “Награждение участников олимпиады”, but the input/output description and constraints are blank.

codeforcescompetitive-programming
CF 1047765 - Фермер Джон и древний камень

The problem statement section is empty, so there’s no way to reconstruct the task being solved. For an editorial, everything downstream depends on the exact rules of the “ancient stone” process, and right now we don’t have the inputs, outputs, or constraints that define…

codeforcescompetitive-programming
CF 1047762 - Братья и сёстры

I cannot reliably locate a clear, authoritative statement of the full problem statement for “Codeforces 1047762 - Братья и сёстры” from the available sources, and the gym archive pages around that ID are fragmented and mixed with multiple unrelated tasks.

codeforcescompetitive-programming
CF 1047763 - Шестёрки

I can absolutely write the full Codeforces-style editorial in that format, but the problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 1047761 - Прямые и окружности

I can’t reliably write a correct editorial for “Codeforces 1047761 - Прямые и окружности” without the actual problem statement. Right now I don’t know: - what the inputs represent (geometry? queries? construction?

codeforcescompetitive-programming
CF 104777N - XOR Construction

We are given a sequence of XOR differences between consecutive elements of a hidden permutation. More concretely, there is a permutation of all integers from 0 to n − 1, and instead of the permutation itself, we are told the XOR between each adjacent pair.

codeforcescompetitive-programming
CF 104777M - Treasure Chest

We are working on a one-dimensional line of integer coordinates. Monocarp starts at position 0. There is a key at position y and a treasure chest at position x.

codeforcescompetitive-programming
CF 104777L - Computer Games

We are given a collection of games, each game having a storage cost and a rating. We want to pick a subset of these games to install on a computer with a limited total storage capacity. The subset must contain at least k games and the sum of their sizes must not exceed m.

codeforcescompetitive-programming
CF 104777K - Financial Discipline

We are simulating a very specific financial process repeated over a fixed number of days. A person starts with zero coins.

codeforcescompetitive-programming
CF 104777J - Complete the Permutation

We are given an array of length $2n-1$ where all odd positions are already fixed and contain all odd numbers from $1$ to $2n-1$. The even positions are empty, and we must fill them using all even numbers from $2$ to $2n-2$, each exactly once.

codeforcescompetitive-programming
CF 104777I - Points and Minimum Distance

We are given an array of 2n integers, and our task is to turn these numbers into n geometric points in the plane.

codeforcescompetitive-programming
CF 104777H - Fancy Arrays

We are counting arrays of length n where each element is a non-negative integer, but not arbitrary arrays. Two restrictions shape what is allowed.

codeforcescompetitive-programming
CF 104777G - Torn Lucky Ticket

We are given a collection of short digit strings, each representing a “ticket fragment”. We are allowed to concatenate any two fragments, in order, forming a longer ticket.

codeforcescompetitive-programming
CF 104777F - Conflict of Interest

We are given a long sequence of food packs that are initially arranged in a fixed order. These packs are consumed two per day, in consecutive pairs, so day 1 uses positions 1 and 2, day 2 uses positions 3 and 4, and so on.

codeforcescompetitive-programming
CF 104777E - Pins and Jumpers

We are simulating a sequential installation process of interval “jumpers” on a line of pins indexed from 1 to n. Each jumper covers a contiguous segment [l, r]. The robot processes jumpers in order.

codeforcescompetitive-programming
CF 104777D - Infinite Card Game

Each card in this game is defined by two numbers: how strong it is when attacking and how hard it is to beat when defending. A card s can defeat another card t if and only if s.attack t.defence.

codeforcescompetitive-programming
CF 104777B - Two Characters, Two Colors

We are given a binary string and, for every position, two alternative “modes”. If we assign the position red, we gain a value $ri$. If we assign it blue, we gain $bi$.

codeforcescompetitive-programming
CF 104777C - Broken Robot

We are simulating a robot that starts at the origin on an infinite grid and must visit a sequence of points in order.

codeforcescompetitive-programming
CF 104777A - Security

We are given multiple independent test cases. In each one, there is an existing password string and a target length for a new password.

codeforcescompetitive-programming
CF 104778A - Треугольник

We are given three positive integers that represent the lengths of three rigid segments. In one move, we are allowed to pick any one segment and change its length by exactly one unit, either increasing or decreasing it, as long as the segment remains positive after the change.

codeforcescompetitive-programming
CF 104778M - Чередующаяся раскраска

We are given a binary string that changes over time through single-character flips. Alongside these updates, we are repeatedly asked a structural question about any substring: how many colors are needed to assign to its characters so that each color class, when read in…

codeforcescompetitive-programming
CF 104778L - Сжатие графа

We are given a simple undirected graph with up to 2000 vertices, represented by its adjacency matrix. From this graph, we must choose exactly k distinct vertices. After choosing them, we remove these vertices and replace them with a single new vertex V.

codeforcescompetitive-programming
CF 104778K - Еще одна точка

We are given a set of points on a number line. We are allowed to place one additional point anywhere on the integer line, including negative positions. For this chosen point $x$, we compute the sum of absolute distances from $x$ to all existing points.

codeforcescompetitive-programming
CF 104778J - Твоя игра

We are given a sequence of questions, each with a nonzero value. Positive values represent questions Polycarp can answer correctly, while negative values represent questions he cannot answer correctly. The game produces a score starting from zero.

codeforcescompetitive-programming
CF 104778I - Ничья

We are given a football season consisting of $n$ matches. Each match ends in exactly one of three outcomes: a win, a draw, or a loss. A win gives $k$ points, a draw gives 1 point, and a loss gives 0 points.

codeforcescompetitive-programming
CF 104778H - Удаление букв

We are given a string made of lowercase letters. The string can be thought of as a sequence of maximal consecutive blocks, where each block consists of identical characters. For example, in aabbbbccc, the blocks are aa, bbbb, and ccc.

codeforcescompetitive-programming
CF 104778G - Одинаковые части

We are given a string of lowercase letters. We must remove exactly k positions, but with a strict rule: no two removed positions can be adjacent in the original string.

codeforcescompetitive-programming
CF 104778F - Ящики

We start with a row of n initial stacks of boxes. Each stack i contains ai boxes. Between every adjacent pair of initial stacks, we insert a new empty stack, so the layout becomes an alternating sequence of original and new stacks: original, new, original, new, and so on.

codeforcescompetitive-programming
CF 104778D - Конструктив с инверсиями

We are asked to construct a permutation of length $n$, meaning an arrangement of numbers from $1$ to $n$ with no repetitions, such that exactly $k$ elements are involved in at least one inversion.

codeforcescompetitive-programming
CF 104778E - Волшебная книга

We are given a very large book with pages numbered from 1 to n. We choose a starting page x and then read every page from x through n inclusive. Each page has a number, and we only care about the last digit of that number.

codeforcescompetitive-programming
CF 104778B - Баскетбол

We are given a sequence of distances for successful basketball shots. Each shot contributes points depending on a threshold value d that we choose. If a shot distance is strictly less than d, that shot is worth 2 points.

codeforcescompetitive-programming
CF 104778C - Две последовательности

We are given two arrays of integers of equal length. Each position i defines a “constraint interval”, but the interval is unordered: the valid range for a candidate integer x at index i is simply the segment between ai and bi, regardless of which one is larger.

codeforcescompetitive-programming
CF 104782J - Parallelogram

We are given several test cases. In each test case there is a collection of stick lengths. From this collection we want to know whether we can pick four distinct sticks such that, after freely rotating and rearranging them in the plane, they can form a parallelogram using all…

codeforcescompetitive-programming
CF 104782C - Basketball

We are asked to construct a target score using only two types of basketball throws: one type adds 2 points and the other adds 3 points. Given an integer n, we need to determine whether it is possible to form exactly n points using some combination of these throws.

codeforcescompetitive-programming
CF 104782M - Dragons

The structure is a tree where each node has a fixed height. Each query gives two nodes, a starting node u, an ending node v, and a dragon power P. The dragon travels along the unique simple path between u and v.

codeforcescompetitive-programming
CF 104782K - Blabla

We are given a static array and asked to count how many contiguous subarrays satisfy a geometric comparison between two different notions of “spread”.

codeforcescompetitive-programming
CF 104782I - KSumT

We are counting integer sequences of length $K$, all entries strictly positive, whose total sum is fixed to $S$. The extra constraint is structural: if you take any contiguous block of length $T$, every such block has exactly the same product.

codeforcescompetitive-programming
CF 104782H - AI Thoughts

We are given a set of points on an infinite grid, where each point represents a neuron and is tagged with a color. For each query, we are also given a sequence of colors.

codeforcescompetitive-programming
CF 104782G - Minimize Sum

We are playing a game on a sequence of numbers using a deque that starts with a single value, zero. At each step, we process the next array element and are forced to interact with one of the two ends of the deque.

codeforcescompetitive-programming
CF 104782F - Suceava

We are given a fixed tree of neighborhoods. Each road is initially controlled by some gang. Over time, roads change ownership: on each day, a specific road is taken over by another gang, meaning that from that day onward its controlling gang changes.

codeforcescompetitive-programming
CF 104782E - Fiboxor

We are given a sequence defined by a recurrence that mixes arithmetic difference, absolute value, and bitwise XOR. The first two values are both 1, and every next value is computed from the previous two using a deterministic rule.

codeforcescompetitive-programming
CF 104782B - The floor is lava!

We are given a rectangular grid where each cell has an integer height. Think of this grid as a terrain map. A number of people start at specified cells and can move one step per second in the four cardinal directions, or choose to stay still.

codeforcescompetitive-programming
CF 104782A - Maximum Distance

We are given two integer arrays of equal length and we are allowed to pick a contiguous segment from the first array and another contiguous segment from the second array. Both chosen segments must have the same length.

codeforcescompetitive-programming
CF 104783O - Organ-free Man

We are given a function defined on non-negative integers where each digit contributes independently through factorials, but with a twist: the function is defined recursively in terms of decimal digits. For a single digit number, the value is simply the factorial of that digit.

codeforcescompetitive-programming
CF 104783C - TomTom Cruise

We are given an undirected graph where each vertex has a cost and each edge also has a cost. A “trip” is any walk that starts at some vertex, traverses at least one edge, and is not allowed to revisit any vertex or reuse any edge.

codeforcescompetitive-programming
CF 104783W - Win Diesel

We are given a graph of cave rooms plus a special node representing the surface. Each room can potentially be connected to other rooms or directly to the surface through “diggable” edges.

codeforcescompetitive-programming
CF 104783T - Tone Banks

We are given a binary grid made of two symbols, and ., which is not just a picture but a recursive structure. Each maximal connected region of a single symbol forms what the problem calls a data blob.

codeforcescompetitive-programming
CF 104783S - Screamers in the Storm

We are asked to count how many valid sequences of length $N$ can be formed, where each element is an integer between $1$ and $K$. The restriction is on adjacent elements: any two neighbors must be coprime.

codeforcescompetitive-programming
CF 104783R - Cyanide Rivers

We are given a long row of communication towers represented by a binary string. Each character corresponds to one tower in order along a line. A 1 means the tower is on dry ground, either on a shore or an island, while a 0 means the tower sits inside a dangerous cyanide river.

codeforcescompetitive-programming
CF 104783P - Bread Pit

We are given a rooted tree that represents a system of tunnels. Each node is either a cave (a terminal node where bread finally ends up) or a gate (an internal node that forwards bread further downward).

codeforcescompetitive-programming
CF 104783I - Eidam-Sand Lair

We have a vertical building indexed by floors, where floor 0 is the surface and positive numbers represent increasing depth underground. A person starts at some floor and wants to reach the surface. There is also a lift starting at its own floor.

codeforcescompetitive-programming
CF 104783F - Burizon Fort

We are given a positive integer $m$. Think of $m$ as defining a set of “coins”, where each coin is a divisor of $m$. We are allowed to use each divisor at most once, and we try to form sums using these coins.

codeforcescompetitive-programming
CF 104783H - Terrace Hill

We are given a sequence of terrace heights laid out on a straight line. Each position represents a terrace of fixed width one, and adjacent positions are effectively contiguous in space. We want to build bridges between selected pairs of terraces.

codeforcescompetitive-programming