brain

tamnd's digital brain — notes, problems, research

43815 notes

CF 106467H - Morrow by Morrow

We are given a structure consisting of elements arranged in a sequence, and the task is to repeatedly process it under a rule that depends on relationships between neighboring or related elements until no further changes are possible.

codeforcescompetitive-programming
CF 106467E - Right & Left

I can’t reliably write a correct editorial for this problem yet because the statement for Codeforces 106467E (“Right & Left / 右灯左行”) isn’t included in your prompt, and I don’t have enough information to reconstruct it without guessing.

codeforcescompetitive-programming
CF 106467A - Spotlights

We are given a one-dimensional strip of positions, and some of these positions contain spotlights. Each spotlight illuminates a contiguous segment around its location, expanding outward with a fixed reach.

codeforcescompetitive-programming
CF 106467C - Star Farming

I don’t have enough information about Codeforces 106467C - Star Farming from what you provided. The statement section in your prompt is empty, so there’s no way to reliably reconstruct: the input format, the actual task being solved, or what the output is supposed to…

codeforcescompetitive-programming
CF 106484L - Pairing Bugcats

We are given all binary strings of length $n$, which we can think of as integers from $0$ to $2^n - 1$. These $2^n$ values must be partitioned into $2^{n-1}$ disjoint pairs, so every number is used exactly once.

codeforcescompetitive-programming
CF 106484J - Bugcat's Mahjong

We are given a deck consisting of $n$ colors, and each color appears exactly four times. The full deck therefore has $4n$ cards, and all individual cards are distinct positions in a random permutation of this multiset.

codeforcescompetitive-programming
CF 106484I - Bugcat's Adventure

We are given an undirected graph where each vertex represents a location containing a main monster. Each monster has a fixed strength. Initially there are no helpers. Over time, a vertex may receive at most one helper monster, also with a given strength.

codeforcescompetitive-programming
Kvant Physics Problem 54

The circuit in Figure 2 consists of an ideal DC source, a network of resistors, and a single ammeter inserted in one branch.

kvantphysics
CF 106484E - Bugcat's Gathering

We are given a directed weighted graph where two travelers start from opposite ends: one begins at node 1 and the other begins at node n. Each edge has a stamina cost if walked normally.

codeforcescompetitive-programming
CF 106484F - Card Game

We are given a stack of uppercase letters arranged from top to bottom. The task is to rebuild these cards into a new sequence by repeatedly removing either the current top card or the current bottom card, and appending that chosen card to the end of a new sequence.

codeforcescompetitive-programming
CF 106484B - Bugcat's Counting Game

We are given a digit-like parameter k between 1 and 9, and a position x. Imagine counting upward from 1, but we do not consider every integer as valid.

codeforcescompetitive-programming
CF 106484C - Bugcat's Unique Queue

We maintain a queue that behaves like a normal FIFO structure, but with one extra rule: every value can appear at most once at any time. The values that may be stored are integers from 1 to m, and we process Q operations that modify or query this structure.

codeforcescompetitive-programming
Kvant Physics Problem 51

A pinhole camera obscura of linear size $L$ forms a real inverted image of a tiger located at distance $u \le 20,\text{m}$.

kvantphysics
Kvant Math Problem 356

No page or problem statement for M356 has been provided, so a solution cannot be constructed.

kvantmathematicsolympiad
CF 106486L - 用户名长度应在 5 位到 12 位之间

The task is centered around validating a username based purely on its length. We are given a single identifier, and the only requirement is to check whether its length falls within a fixed inclusive range.

codeforcescompetitive-programming
CF 106486H - Silly Tree

We are asked to count rooted ordered trees on exactly $n$ nodes under a structural constraint on branching. Each node has some number of children, and this number must belong to a given allowed set $A$.

codeforcescompetitive-programming
CF 106486G - 远交近攻

We are given a line of positions from 1 to n, each position holding some initial amount of resources. Initially every position is its own independent group, so there are n disjoint groups, each containing exactly one index.

codeforcescompetitive-programming
CF 106486E - Excel 的列编号

We are given a sequence of queries, each query is a large positive integer representing a column index in a spreadsheet system that labels columns using letters instead of numbers.

codeforcescompetitive-programming
CF 106486B - 机械猫的流浪

We are given a robot cat moving along a straight path of positions from 1 to $n+1$. It starts at position 1 at time 0 and wants to reach position $n+1$. Each move to the next position consumes exactly one unit of time. Energy is the critical constraint.

codeforcescompetitive-programming
CF 106486C - 跟我的漫游者说去吧

We are looking at a game mechanic where the probability of landing a critical hit is not fixed, but depends on how long it has been since the previous critical hit. The longer you go without a crit, the higher the chance becomes, up to a cap of 1.

codeforcescompetitive-programming
CF 106494F - Thanos Sort

We are given an array that can be recursively split into halves, and at each segment we are allowed to decide whether to “stop” or to continue splitting.

codeforcescompetitive-programming
CF 106494D - Alternative Worlds II

We are given an array of numbers and we are allowed to split it into several disjoint groups. For each group, we compute its median, and the score of a partition is the sum of these medians. The task is to choose a partition of the array that maximizes this total score.

codeforcescompetitive-programming
CF 106494C - Alternative Worlds I

We are given a list of integers and we are allowed to split them into several groups. For each group, we compute its median, and the final score is the sum of all these medians. The task is to choose the partition of the array into groups that maximizes this total sum.

codeforcescompetitive-programming
CF 106494A - Random Order

We are given a permutation-like sequence of positions derived from the original array: instead of working with values directly, we only care about the index position of each element in the given ordering. These indices form an array $i1, i2, dots, in$.

codeforcescompetitive-programming
Kvant Physics Problem 49

A U-shaped tube of constant cross-sectional area $A$ is completely filled with water of density $\rho$.

kvantphysics
Kvant Physics Problem 47

An ideal gas is taken through two different quasi-static processes between the same initial state $A$ and final state $C$.

kvantphysics
Kvant Math Problem 354

The problem statement for M354 is not included in your message, and I also do not have the scanned page containing it.

kvantmathematicsolympiad
CF 106503L - As crychic wanes

We are given a rooted tree with node 1 as the root. Each node has a weight, and on any given day, the weight of most nodes is fixed, but a small set of special nodes shares a single global value that can change each day.

codeforcescompetitive-programming
CF 106503H - Hajimi's Rebellion

I’m sorry, but I can’t reliably write a complete editorial and accepted solution for this problem from the statement alone. This is a highly nontrivial dynamic-tree problem.

codeforcescompetitive-programming
CF 106503I - 「I」nan desu

We are given a binary grid made of black and white cells. Each test case provides an $n times m$ matrix where each cell is either black () or white (.). The task is to count how many subrectangles of this grid form a special pattern called an “I”.

codeforcescompetitive-programming
CF 106503E - Top Student ProblemⅠ

We are given a very small 3 × 3 grid where each cell contains a height value between 0 and 3. You can think of this as a top-down projection of a stack of unit cubes: at position (i, j), there are hi,j cubes stacked vertically.

codeforcescompetitive-programming
CF 106503F - Top Student ProblemⅡ

We are given a rectangular grid of size $n times m$ where we may place stacks of unit cubes, so each cell contains a non-negative integer height. We do not see the grid directly. Instead, we are given two projections of the same 3D structure.

codeforcescompetitive-programming
CF 106503C - Valentine's Day of Crime and Punishment

We are dealing with a 64 by 64 grid of bits, where each cell is either 0 or 1. Exactly one cell is special, and Alice is told its coordinates.

codeforcescompetitive-programming
CF 106503A - Hello, SCNUCPC!

We are given a row of $n$ positions, each position either already fixed as the letter C or still empty, represented by ?. We must replace every ? with uppercase letters so that the final string contains exactly $k$ occurrences of the pattern SCNUCPC.

codeforcescompetitive-programming
CF 106473C - Потенциал Бибопа

We are given a string over lowercase Latin letters. The string is first compressed into maximal consecutive segments of identical characters, and the cost of the string is the sum of squares of the lengths of these segments.

codeforcescompetitive-programming
CF 106473A - Экзамен на героя

We start with a system described by three numbers. There is a value on a display, initially a, and a current “power” value b. The goal is to transform the display value into exactly c while simultaneously reducing the power until it becomes zero.

codeforcescompetitive-programming
CF 106367I - Fireflies Lead the Way

We are given a line of $n$ lamps placed along a river at increasing coordinates $x1 < x2 < dots < xn$. A traveler starts at lamp 1 and wants to reach lamp $n$. At each lamp $i$, there are two ways to move forward.

codeforcescompetitive-programming
CF 106367C - Shichieichou's Guidance

We are given a rooted tree whose root is node 1. Every leaf lies at the same depth, so the tree is perfectly balanced with respect to leaf depth, although the branching structure can be arbitrary. Each butterfly is attached to a node and disappears at a specified time.

codeforcescompetitive-programming
CF 106367G - True Blue

We are given an array of non-negative values, where each position represents how much “blue resource” a block currently holds. Over time, we receive operations of the form asking about a segment of this array and a threshold value.

codeforcescompetitive-programming
CF 106367B - Whalica's Permutation Construction

We are asked to construct a permutation of numbers from 1 to n such that a specific divisibility condition holds at every prefix. For a permutation p, define a running prefix sum Si as the sum of the first i elements.

codeforcescompetitive-programming
CF 106363H - Broken Heart

We are given two polygonal shapes made of straight edges, and we are allowed to move one shape relative to the other.

codeforcescompetitive-programming
CF 106363E - The Perfect Gift

We are given a collection of ticket prices and asked to solve a two-level selection task. First, among all pairwise differences between ticket prices, we need to determine the k-th smallest difference value.

codeforcescompetitive-programming
CF 106363C - Supply and Demand

We are given a sequence of values representing some quantity that is already sorted in non-decreasing order. The task revolves around examining contiguous subsections of this sequence and reasoning about their averages.

codeforcescompetitive-programming
CF 106362H - Love Triangles

We are given an undirected simple graph. Each vertex represents a node in a network, and each edge represents a mutual connection between two nodes.

codeforcescompetitive-programming
CF 106362E - I Wanna Know...

We are given a collection of tickets, each with a numeric price. From these prices we are interested in the differences between pairs of tickets.

codeforcescompetitive-programming
CF 106356L - Sapure

We are simulating a snake moving on an $n times n$ grid where edges wrap around, so the grid behaves like a torus. The snake starts as a single cell at $(1,1)$.

codeforcescompetitive-programming
CF 106356G - Genome Evolution

We are given a system that generates a sequence of integers, where each integer represents a genome encoded as a bitmask. Each bit indicates whether a particular genetic marker is present. The evolution rule is deterministic. The first two genomes are fixed as $a$ and $b$.

codeforcescompetitive-programming
CF 106356B - Easy Composite

We are given several prime numbers. For each prime $p$, we may place one or more decimal digits in front of its decimal representation. The resulting number is the concatenation of the chosen prefix and $p$.

codeforcescompetitive-programming
CF 106356A - Quantum Corridor

We are given a one-dimensional corridor of chambers numbered from 1 to n. A particle starts at a fixed chamber i. From any chamber, it can attempt to move left or right by exactly a steps, or by exactly b steps.

codeforcescompetitive-programming
CF 106353G - Group Photo

We are given a sequence of distinct heights arranged in a line. We are allowed to pick some of the people and freely rearrange only those selected people among themselves, while everyone else stays exactly at their original positions.

codeforcescompetitive-programming
CF 106353B - Bisecting Bargain

We are given a target amount of money $n$ in euros, but the way this money is represented is not fixed. An ATM will always hand out some multiset of standard euro denominations whose total value is exactly $n$.

codeforcescompetitive-programming
CF 106352B - Тренировка по пейнтболу

We are given a sequence of paintballs, each characterized by a time moment when it flies and a vertical position (a row on a wall). The wall has height h, and rows are numbered from bottom to top. Each paintball exists only at its given time and affects exactly one row.

codeforcescompetitive-programming
CF 106339H - Do You Want to Build a Snowman?

We are given a sequence of non-negative integers representing available snow amounts along a line. The task is to choose three contiguous or non-overlapping portions of this sequence and assign them to three snowballs, whose sizes are denoted s1, s2, and s3 after sorting so…

codeforcescompetitive-programming
CF 106339D - Snowball

We are given a sequence of skeleton spawn times along with a final time horizon $k$. A single action can be performed exactly once: at some chosen time $t$, a snowball is thrown that instantly destroys all skeletons that have already appeared.

codeforcescompetitive-programming
CF 106338D - XOR Раскраска

We are given two arrays, which we can think of as two sets of integers, A and B. From these two sets we implicitly define a compatibility rule between elements of A.

codeforcescompetitive-programming
CF 106337C - Расстановки фишек

We are working with a grid and a collection of rectangular “forbidden zones” defined by their bottom-right corners. Each constraint $(ri, ci)$ describes the full rectangle from $(1,1)$ up to $(ri, ci)$.

codeforcescompetitive-programming
CF 106328M - Classic Revisited

We are given a sequence of integers and asked to extract a subsequence that reads the same forward and backward, with the additional constraint that its length must be even.

codeforcescompetitive-programming
CF 106328H - Distinct Substrings

We are given a string over lowercase English letters. For every position in this string, we want to count how many distinct substrings of the string “cover” that position.

codeforcescompetitive-programming
CF 106328D - Xor And Mul

We are given two integers $n$ and $m$, and we need to count how many ordered pairs $(x, y)$ exist such that $0 le x le n$ and $0 le y le m$, and a bitwise identity holds: $$(x & y) cdot (x oplus y) = x cdot y.

codeforcescompetitive-programming
CF 106318A - Две доминошки

We are given two domino tiles. Each tile has two numbers written on its ends. We are allowed to rotate a tile, meaning we can swap its two ends, but we cannot change the numbers themselves.

codeforcescompetitive-programming
CF 106315F - Over Counting

We are given a binary string and we are allowed to permute its characters in every distinct way. For each resulting arrangement, we define a two-level “inversion counting process” on the binary array.

codeforcescompetitive-programming
CF 106307F - Is this Fibonacci

We are given a number written as a string, potentially very large, and we are asked to decide whether its value appears in the Fibonacci sequence defined by starting values f0 = 1 and f1 = 1, with every next term formed by summing the previous two.

codeforcescompetitive-programming
CF 106299C - Saki and Separation

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only see “C” with no description of the task, inputs, outputs, or constraints. Without that, any solution would be guesswork and would almost certainly be wrong.

codeforcescompetitive-programming
CF 106298L - Enigmatic Game

Thinking

codeforcescompetitive-programming
CF 106298D - Breezy GCD Problem

We are given a collection of integer intervals. Each interval represents a range of allowed values, and we are trying to determine whether there exists a single integer that behaves consistently across all intervals under a GCD-like constraint.

codeforcescompetitive-programming
CF 106293C - Кося любит битмаски!

We are given an array of integers and we want to split it into a maximum number of consecutive non-empty segments that cover the whole array.

codeforcescompetitive-programming
CF 106290K - 餐券设计

I can’t write a correct editorial for this yet because the actual problem content is missing. Right now we only have the title “餐券设计” (voucher/coupon design), but no description of what the input represents, what transformations are required, or what the output…

codeforcescompetitive-programming
CF 106290G - 回文串魔法

I can’t reliably write a correct Codeforces-style editorial for this yet because the actual problem statement is missing from your prompt (the input/output sections are empty, and “回文串魔法” alone isn’t enough to reconstruct the task uniquely).

codeforcescompetitive-programming
CF 106289B - Card Game

I can’t reliably write a correct editorial for this yet because the actual problem content is missing. Right now, the statement only shows: - Problem: “Card Game” - No rules of the game - No input format - No output format - No constraints - No samples A Codeforces…

codeforcescompetitive-programming
CF 106272F - 蛇球

The problem statement is effectively empty here, so there is no way to reconstruct what Codeforces 106272F (“蛇球”) is asking. An editorial depends entirely on knowing the operations on the input, the constraints, and what is required to be computed.

codeforcescompetitive-programming
CF 106270D - Save the Wonderland

We are given a tree, meaning a connected graph with no cycles, where there is exactly one simple path between any two cities. We want to place exactly K guards on K chosen cities.

codeforcescompetitive-programming
CF 106268L - Common Tangent Lines

Thinking

codeforcescompetitive-programming
CF 106268D - Decompose and Concatenate

We are given a single large integer $N$, up to $10^{17}$. We are allowed to split it into two positive integers $a$ and $b$ such that $a + b = N$.

codeforcescompetitive-programming
CF 106267F - Floral CatastrophE

I can’t write a correct, detailed editorial for this yet because the actual problem content for “Floral CatastrophE (Codeforces 106267F)” is missing from your prompt.

codeforcescompetitive-programming
CF 106263H - SCNU LOGO

The task starts with a fixed ASCII logo: a small grid made of and . characters with dimensions 5 rows by 36 columns. You are given a scaling factor k, and you must output a new grid where every original character becomes a solid k × k block of the same character.

codeforcescompetitive-programming
CF 106262M - Web Delivery

We are given several independent scenarios where Gagamboy needs to buy one kilogram of each of several chemical types. There are multiple online sellers, and every seller sells every chemical, but the price depends on both the chemical and the seller.

codeforcescompetitive-programming
CF 106262G - Max Cut Min Flow

We are given a straight line of checkpoints from 1 to n. Water always flows strictly forward from checkpoint 1 to checkpoint n, and the only way to stop flooding is to block at least one of the n − 1 connections between consecutive checkpoints.

codeforcescompetitive-programming
CF 106252I - Volunteer Simulator

We process a chronological stream of accepted submissions in a programming contest. Each submission belongs to a team and a problem, and all submissions are already successful ones, so every line represents a correct solution attempt.

codeforcescompetitive-programming
CF 106252C - Buggy Painting Software II

We are given a two-phase system where we first construct a set of “color images”, and later must decode them after a lossy transformation. Each image consists of a sequence of length $3m$.

codeforcescompetitive-programming
CF 106251C - Marbles

We are given a permutation on the integers from 1 to n, meaning every position points to exactly one other position, and every position is pointed to exactly once.

codeforcescompetitive-programming
CF 106250D - Exam Room

We are given a set of points in the plane with a fixed origin point $O$. The task is to count how many subsets of these points are “valid” under a geometric constraint that depends on distances and angles relative to $O$.

codeforcescompetitive-programming
CF 106241M - Ultimate K-Query

We are given an array of length n, and we need to answer q queries. Each query asks about a subarray, but the endpoints of that subarray are not taken directly from the input.

codeforcescompetitive-programming
CF 106241H - Yasser and Arithmetic Sequences

We are given an array and we are allowed to slightly adjust each element, but only once per position, and the adjustment is extremely limited: for each index we can either do nothing or add/subtract an integer between 1 and 10.

codeforcescompetitive-programming
CF 106241B - Bouncing Chaos

We are simulating two identical billiard balls moving inside a rectangular grid of size $n times m$. Each cell has integer coordinates $(i, j)$, and both balls start from interior positions, never on the boundary.

codeforcescompetitive-programming
CF 106239H - 能量汇聚

We are standing on a line of positions labeled from 0 to n. Position 0 is the start and has no reward, while every position from 1 to n contributes a fixed energy value if we land on it. We begin at position 0 and want to reach position n. Movement is constrained in two ways.

codeforcescompetitive-programming
CF 106239D - 环球旅行商

The map consists of rows from 0 to n+1 and columns from 1 to m. Rows 0 and n+1 represent the north pole and south pole. Every supply point lies inside rows 1...n. From a cell (x,y) we may move south to (x+1,y), or move left and right inside the same row.

codeforcescompetitive-programming
CF 106238L - Quantum Computing Programming

This problem has no input. We start with three qubits. The first qubit contains an arbitrary unknown state $$alpha while the second and third qubits are both initialized to $ The task is to output a program in the given HYW language.

codeforcescompetitive-programming
CF 106238E - Reliable Piglet

I do not have enough information to write a correct editorial for Codeforces 106238E - Reliable Piglet. The material you provided contains only the title and empty input/output sections.

codeforcescompetitive-programming
CF 106238G - Gift

I can't write a correct editorial for this problem from the information provided. The prompt identifies the task as "Codeforces 106238G - Gift", but the attached statement is missing.

codeforcescompetitive-programming
CF 106238D - Song of Loneliness

I can write the editorial, but the problem statement you provided is incomplete. For Codeforces 106238D, the only visible text is: - "D" - "概率论" - "文本比较" The actual description, input format, output format, and constraints are missing.

codeforcescompetitive-programming
CF 106225H - Hyper Smawk Bros

The game starts with a boss whose health is n. Two players attack alternately and you move first. Every attack deals some integer damage between 1 and m. The only restriction is that a player cannot repeat the amount that the opponent used on the immediately preceding turn.

codeforcescompetitive-programming
CF 106225D - Dungeon Equilibrium

We are given an array where each value represents a monster type. A level is considered balanced when every type that remains appears exactly as many times as its own value. For example, if type 4 is present, then it must occur exactly four times.

codeforcescompetitive-programming
CF 106210A - 最大子串匹配删除操作

all in the style and formatting you specified.

codeforcescompetitive-programming
CF 106208F - Time Well Spent

I can do this, but the problem statement in your message is corrupted and incomplete. Several critical pieces are missing or malformed: - The first line says The first line contains one integer t, but the sample input does not contain t.

codeforcescompetitive-programming
CF 106208D - The New CEO of CloseAI

We are given a collection of words separated by spaces. Initially every character is its own token. At any moment, every word is represented as a sequence of tokens rather than a sequence of characters. During one iteration we examine every adjacent pair of tokens in every word.

codeforcescompetitive-programming
CF 106203B - Пирамида Видений

We are given a triangular array with n rows. Row i contains exactly i integers. The process starts from the top row and repeatedly destroys rows one by one until only the bottom row remains.

codeforcescompetitive-programming
CF 106203I - Проблемы бритья

We are given a grid representing a face. Each cell is marked as either a required shaving area, a forbidden area, or an irrelevant area. The goal is to determine whether we can remove all required cells marked with “+” using a razor.

codeforcescompetitive-programming
CF 106203F - Ларёк и две куклы

We are given two integers representing values stored in two separate “cursed dolls”. Let us call them the first value and the second value. We are also given two parameters that define a synchronized operation.

codeforcescompetitive-programming
CF 106203A - Луч смерти

We are maintaining a dynamic set of points on the plane. Each operation either inserts a new point or removes an existing one, and after every operation we must answer a yes/no question: whether all currently present points can be covered by a single infinite straight line.

codeforcescompetitive-programming
CF 106208C - Max Person

We are given an unlimited tower of floors. Each floor has exactly $n$ rooms, and each room can hold one person. Placing a person on floor $x$ costs $2x$ units of budget, and we are allowed to place multiple people on the same floor as long as we do not exceed $n$ people there.

codeforcescompetitive-programming