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tamnd's digital brain — notes, problems, research

41641 notes

CF 106293D - Муся и какой-то XOR

We are given an array of integers and asked to extract as many disjoint contiguous segments as possible such that each chosen segment has XOR equal to zero.

codeforcescompetitive-programming
CF 106292D - Elephant Filimon and the Digit Three

We are given a number and allowed to repeatedly modify it using a very specific operation. In one move, we pick any positive integer whose decimal form is made only of the digit 3, such as 3, 33, 333, and so on, and add it to the current value.

codeforcescompetitive-programming
CF 106290D - 小丑牌

I can’t reliably write a correct editorial for this yet because the actual problem content for “Codeforces 106290D - 小丑牌” is missing from your message (the statement section is empty).

codeforcescompetitive-programming
CF 106272I - Euler

I can’t write a correct editorial yet because the actual problem statement for “Codeforces 106272I - Euler” is missing from your prompt.

codeforcescompetitive-programming
CF 106268B - Minimizing Wildlife Damage

We are given a line of farmland split into $n$ consecutive plots. Each plot initially contains some amount of wheat.

codeforcescompetitive-programming
CF 106267B - 排列之差

I don’t have the actual statement of Codeforces 106267B - 排列之差 available in your prompt (the “Input/Output” section is empty), so I can’t reconstruct a correct algorithm or editorial without risking hallucinating the problem.

codeforcescompetitive-programming
CF 106262L - Trace of Product of Sparse Square Matrices

We are given two very large square matrices $A$ and $B$, but they are not provided in full. Instead, each matrix is described only by its nonzero entries. Every missing position is implicitly zero, and the number of nonzero entries is small compared to $n^2$.

codeforcescompetitive-programming
CF 106252B - Buggy Painting Software I

We are given a target image on an $n times m$ grid. Each cell contains either a color label or zero, where zero means transparent.

codeforcescompetitive-programming
CF 106251D - Introduction to Number Theory

We are given an array of integers, and we want to determine whether there exists a special value $X$ such that the array can be split into two groups with a very strong number-theoretic relationship to $X$.

codeforcescompetitive-programming
CF 106250A - 67

We are working with an unknown array of positive integers indexed from 1 to N. A key structural promise is that any two different elements of this array are coprime, so their greatest common divisor is always 1.

codeforcescompetitive-programming
CF 106241L - Extended Modulo Queries

We are given an array of integers where both the array values and the modulus values are bounded by 50,000. Each query does not ask for a single computation, but for a nested sum: we pick a segment of the array and then, for every modulus value in a given range, we compute the…

codeforcescompetitive-programming
CF 106239N - 最大化仿射变换

We are given a collection of affine transformations of a single integer variable, all starting from zero. Each operation takes the current value of $x$ and replaces it with $ai x + bi$, where both coefficients are non-negative integers.

codeforcescompetitive-programming
CF 106238I - Heart Lingers, Future Fades

The problem statement for “Codeforces 106238I - Heart Lingers, Future Fades” is effectively empty in the input you provided. There is no description of the input format, output format, constraints, or even the computational task itself beyond the title line.

codeforcescompetitive-programming
CF 106225B - Billion Players Game

We are given a range of possible outcomes for a hidden integer value $p$, which represents Godflex’s final ranking. We only know that $p$ lies somewhere in an interval $[l, r]$, and nothing more. Alongside this uncertainty, there are several bookmaker offers.

codeforcescompetitive-programming
CF 106208A - Interval and Expected Value

We start with a segment of integers $[l, r]$. At any moment, the process maintains two things: the current segment and a running score initialized to zero. Each round consists of two random choices.

codeforcescompetitive-programming
CF 106203D - Великая теорема Фестера

We are given a very small and unusual restriction on the exponent in a power equation of the form $a^n + b^n = c^n$. Unlike classical number theory settings where $n$ is large, here $n$ is guaranteed to be either 0 or 1.

codeforcescompetitive-programming
CF 106202B - Торговцы

We are given a line of merchants, each holding a single item with a price. The price of the i-th merchant is an integer in the range from 0 to $2^k - 1$, and every price is conceptually stored as a fixed-length k-bit binary number. The system processes three types of operations.

codeforcescompetitive-programming
CF 106201A - Нестандартный подход

We are given an $n times m$ grid, and we are allowed to choose a single starting cell on the boundary of this grid. From that chosen cell, a process starts that spreads to all four neighboring cells each second, exactly like a breadth-first expansion on a grid.

codeforcescompetitive-programming
CF 106200D - Задача ЛесКлассШколы

We are given a sequence of non-negative integers, and we are allowed to optionally apply a digit-reversal operation to any element. Each number can be reversed independently, but only once. After performing these choices, we obtain a final array, and we want to maximize its mex.

codeforcescompetitive-programming
CF 106199D - Творец воспоминаний

We are simulating a process of placing small fixed shapes into a large grid, where the grid behaves like a physical system: cells get filled, whole rows disappear when completely filled, and everything above a removed row collapses downward.

codeforcescompetitive-programming
CF 106194B - 共鸣护符

We are given a closed interval of integers from L to R, and we must arrange all these integers into a permutation so that the ordering between any pair of numbers depends entirely on whether they are coprime.

codeforcescompetitive-programming
CF 106193A - Asynchronous Processor

We are simulating a very small programming language that modifies a single integer register $A$, starting from zero. Each instruction either adds a value to $A$ or overwrites $A$ completely with a value.

codeforcescompetitive-programming
CF 106192A - Проверка комнат в ГЗ

The building can be thought of as a fixed catalog of rooms distributed across floors, where each floor has a known set of possible room slots and each slot corresponds to one or two actual living places.

codeforcescompetitive-programming
CF 106185A - 2025

We are given a sequence of test cases. Each test case contains a single integer $n$, and for each one we conceptually build an $n times n$ multiplication table where the cell in row $a$ and column $b$ contains the product $a cdot b$.

codeforcescompetitive-programming
CF 106184B - 天才琪露诺与雾之湖的宝藏

I can’t reliably write a correct editorial from what you’ve provided because the actual problem statement is missing. Right now I only see the title “Codeforces 106184B - 天才琪露诺与雾之湖的宝藏”, but the input/output and rules are blank.

codeforcescompetitive-programming
CF 106175B - Watchdog

We are given a square roof with integer coordinates, from $(0,0)$ to $(S,S)$, and a set of hatch positions inside it. We must choose a single point on the roof where a leash is attached.

codeforcescompetitive-programming
CF 106170G - Nearest Strings

We are given several short strings made of lowercase letters, and for each string we want to find another string in the same set that is “closest” under a specific distance measure.

codeforcescompetitive-programming
CF 106167D - Decrypting Zodiac

We are given two strings of equal length. One is the observed encrypted text, and the other is a candidate original message that we believe might have been encrypted to produce it. The encryption process is two-layered.

codeforcescompetitive-programming
CF 106164H - Home Workout Playlist

We are given a sequence of song “hype” values in a fixed order, and we are allowed to delete some songs while keeping the remaining ones in their original relative order. From the remaining subsequence, we want a very structured pattern.

codeforcescompetitive-programming
CF 106163B - Shortest Path

We are given a complete graph on n cities, where every pair of cities has a direct road. The cost of that direct road is not uniform: it depends on the bitwise AND of the two city values.

codeforcescompetitive-programming
CF 106161G - GCD of Subsets

We are given a collection of items. Each item has a weight and a value, but for some items exactly one of these two numbers is missing and must be assigned by us as a positive integer not exceeding one billion. Two greedy procedures will later run on the completed dataset.

codeforcescompetitive-programming
CF 106159C - Creating a Playlist

We are given a sequence of songs, each associated with a value that can be positive or negative. We want to select a subset of these songs to maximize the total sum of selected values, but there is a spacing restriction: if we choose a song at position i, then we are forbidden…

codeforcescompetitive-programming
CF 106158B - Magic Circle

We have $n$ wizards arranged in a circle, indexed from 1 to $n$. Each wizard starts with a very large identical mana value, so initially all wizards are tied. Then we apply $q$ rituals. Each ritual defines a sequence of affected wizards.

codeforcescompetitive-programming
CF 106153D - 琪露诺的无限循环小数

The task revolves around deciding whether a given fraction produces a terminating decimal or an infinite repeating decimal when written in base 10. Each test case gives an integer denominator, and we implicitly consider the fraction $frac{1}{n}$.

codeforcescompetitive-programming
CF 106151I - runnerups

We are given an array of distinct performance scores recorded over time. Each query provides a small set of time indices, and from those indices we consider every possible interval formed by choosing two of them as endpoints, including choosing the same index twice only when…

codeforcescompetitive-programming
CF 106144C - Monocarp, Polycarp and Brackets

We are given a string of brackets. Two players alternately remove characters from the ends of this string. On each move, a player picks either the leftmost or rightmost character of the current string and deletes it.

codeforcescompetitive-programming
CF 106142F - Сделать максимальным

We are given an array of integers, and for every position we must answer a separate optimization question about that position’s value. The element at index i is treated as a fixed reference element.

codeforcescompetitive-programming
CF 106141J - Exercise for Dania

We are given an array and for every prefix of this array we must compute a value formed from all unordered pairs inside that prefix.

codeforcescompetitive-programming
CF 106136N - In Filtration

We are working on an infinite grid where a white king starts at a given coordinate and must eventually capture all black rooks. The king moves like a standard chess king, meaning it can step to any of the eight neighboring cells in one move.

codeforcescompetitive-programming
CF 106132D - Permutation Swaps

We start with the identity permutation, meaning the array contains numbers from 1 to n in increasing order. We are allowed to repeatedly apply a recursive construction that behaves like a binary splitting process.

codeforcescompetitive-programming
CF 106130A - \%\%\%自动机

The task reduces to constructing a single string based on an input integer. We are given a number $n$, and we must output a line consisting of exactly $n$ identical characters, where each character is the percent symbol %.

codeforcescompetitive-programming
CF 106129K - Karlsruhe Skyline

We are asked to construct a single permutation of the numbers from 1 to n, interpreted as building heights along a row. Two integers a and b describe how many buildings are visible when looking from the left end and from the right end respectively.

codeforcescompetitive-programming
CF 106084H - Chopsticks

We start with a collection of chopsticks grouped by type. Each type contributes a known number of identical items. From the full pool, we randomly select exactly 2n chopsticks without replacement.

codeforcescompetitive-programming
CF 106084D - Palindromic Distance

We are given a string for each test case and we want to measure how far it is from being a palindrome, where “distance” is the standard edit distance with insertions, deletions, and substitutions allowed.

codeforcescompetitive-programming
CF 106082K - Security Fence

We are given a simple closed fence described by its corner points in clockwise order. The fence forms a convex polygon, so every interior angle is less than 180 degrees and every line segment between two interior points stays inside the region.

codeforcescompetitive-programming
CF 106082I - Share Auction

I can’t write a correct editorial for this problem yet because the actual problem statement is missing. Right now I only see the title “Share Auction” with no rules about bids, constraints, input format, or what needs to be optimized.

codeforcescompetitive-programming
CF 106082B - Simplified Calendar System

I’m missing the actual problem statement for Codeforces 106082B - Simplified Calendar System. Right now the input/output sections are empty in your prompt, so there’s no way to correctly reconstruct: - what the calendar system defines (days, months, weeks, etc.

codeforcescompetitive-programming
CF 106073M - Minas Gerais' walls

We are given a one-dimensional wall made of consecutive segments, each segment having an initial height. We are allowed to perform exactly one reinforcement operation.

codeforcescompetitive-programming
CF 106073H - How many teams?

Each student in this problem can be represented by a bitmask of length $K$, where the $j$-th bit indicates whether the student has a particular frontend skill.

codeforcescompetitive-programming
CF 106073C - Collatz polynomial

We are given a polynomial where every coefficient is either 0 or 1, so the polynomial is best thought of as a set of powers of x. If the coefficient of $x^k$ is 1, we include that term, otherwise we do not.

codeforcescompetitive-programming
CF 106072H - Tree Shuffling

We are given a tree where every vertex initially carries a distinct label equal to its index. The only allowed action is a single global operation that changes some of these labels. In that operation, we first pick a simple path in the tree.

codeforcescompetitive-programming
CF 106072C - Jiaxun!

We are given a pool of programming problems, each problem already labeled by exactly which of three students can solve it. Every problem falls into one of seven categories depending on its solvability set among students 1, 2, and 3.

codeforcescompetitive-programming
CF 106068J - Washing Machine

We are given a fixed amount of time, measured in hours, during which electricity is available. Each hour corresponds to exactly one washing cycle of a machine. There are several colors of clothes, and each color has a certain number of items that must all be washed.

codeforcescompetitive-programming
CF 106068D - Ba3d Khamsa

We are given a string, and we are asked multiple independent queries on it. Each query focuses on a contiguous substring. For that substring, we are allowed to modify characters, where one operation means replacing a single character with any other lowercase English letter.

codeforcescompetitive-programming
CF 106059M - Median Replacement

We are given an array, and we repeatedly apply a randomized operation on it. One step of the process picks an index uniformly at random and overwrites that position with the median of the remaining elements.

codeforcescompetitive-programming
CF 106059H - Huge Subsets

We are given an array of positive integers. For each $k$, we look at all ways to choose exactly $k$ elements and record the sum of each such choice. This produces a multiset $Sk$, where repetition matters because different subsets can produce the same sum.

codeforcescompetitive-programming
CF 106059B - Binary Palindromes

We are given a binary string $s$. We are allowed to cut it into a sequence of contiguous pieces, and the cut points are completely flexible, meaning every split of the form “choose $k$ and break into $k$ substrings” is valid, and all such splits are counted.

codeforcescompetitive-programming
CF 106057H - Mr. Benzene's Bachelor Trip

We are given two integers, $k$ and $m$. Think of building a target sum $n$ by splitting it into exactly $k$ ordered parts, where each part is a non-negative integer. Two decompositions are different if any position in the $k$-tuple differs.

codeforcescompetitive-programming
CF 106057C - Prime Dominion

We are given an integer array and we want to examine every contiguous segment of it. For each segment, we compute the greatest common divisor of all elements inside that segment.

codeforcescompetitive-programming
CF 106054H - Hidden divisor

We are given a multiset of divisors of an unknown integer $X$, but one divisor is missing. In total, $X$ has exactly $N+1$ positive divisors, and we are given $N$ of them.

codeforcescompetitive-programming
CF 106054C - Circularly

We are given a permutation of length $N$, meaning it contains each number from 1 to $N$ exactly once. From this permutation, we define a transformation called “taking a semi-fixed point”: an index $x$ is counted if applying the permutation twice brings us back to $x$…

codeforcescompetitive-programming
CF 106047L - Difficult Constructive Problem

We are given a binary string where some positions are already fixed as 0 or 1, while others are unknown and marked with ?. We must replace every ? with either 0 or 1. After filling the string, we look at adjacent pairs and count how many times consecutive characters differ.

codeforcescompetitive-programming
CF 106047K - Are you a bot?

We are given a target array $b$ of length $n$. Our task is not to compute a value from a permutation, but to reconstruct a permutation $a$ of numbers from $1$ to $n$ such that a derived function computed from $a$ matches $b$.

codeforcescompetitive-programming
CF 106047H - Not Another Path Query Problem

We are given an undirected graph where each edge carries a 60-bit weight. A path between two vertices is evaluated not by summing or minimizing weights, but by taking the bitwise AND of all edge weights along that path.

codeforcescompetitive-programming
CF 106047E - Computational Geometry

We are given a convex polygon with vertices listed in counterclockwise order. From this polygon, we must choose three vertices, call them $a$, $b$, and $c$, also in counterclockwise order along the boundary.

codeforcescompetitive-programming
CF 106047B - Be Careful 2

We are working inside an axis-aligned rectangle whose lower-left corner is fixed at the origin and whose upper-right corner is at $(n, m)$. Inside this rectangle there are $k$ forbidden lattice points.

codeforcescompetitive-programming
CF 106047C - Connected Intervals

We are given a tree with vertices labeled from 1 to n, and these labels also define a linear order. For any interval [l, r], we look at the vertices whose labels lie in this range and consider the subgraph induced by them in the original tree.

codeforcescompetitive-programming
CF 106039C - Echoes of the Jade Library

We are given a sequence of N strings, each string representing a “scroll” written with lowercase letters. From each scroll, we care about all substrings that are palindromes, and we treat two substrings as the same if their character sequences are identical, regardless of…

codeforcescompetitive-programming
CF 106039A - Yuyuan Market

We are given a sequence of length $2N$, where each value from $1$ to $N$ appears exactly twice. You can think of it as pairs of identical symbols placed along a line. The task is to choose pairs of equal symbols under a strict movement rule.

codeforcescompetitive-programming
CF 106039M - Nomad

We are given a fixed number of nights, D, and a collection of N possible places where a person can sleep. Each place i comes with a constraint di that limits how many consecutive nights can be spent in that place.

codeforcescompetitive-programming
CF 106039L - Game of Life

We are given a very small grid, at most 8 by 8, where each cell can be in one of three states. A cell can be alive, dead, or blocked. Blocked cells never change and also never participate as active contributors in the dynamics. The system evolves in discrete steps.

codeforcescompetitive-programming
CF 106039K - Cake Hater

We are given a set of ingredients and a list of ingredients that Antonio refuses to use. The recipe is split into several stages, and each stage specifies a subset of ingredients required for that step. When Antonio prepares a stage, he simply omits every ingredient he dislikes.

codeforcescompetitive-programming
CF 106039I - Bath

We are given a simple polygon representing a room, with the first vertex acting as a door. Inside this polygon lies a single point representing a towel. A person starts at the door vertex, walks entirely within the polygon, reaches the towel, and must return to the same door.

codeforcescompetitive-programming
CF 106039H - The Wisdom of Master Wei

We are given two starting years, one for Master Wei and one for Kai. From those years onward, each person accumulates “experience” equal to the number of years that have passed since they started programming.

codeforcescompetitive-programming
CF 106039G - Incompatible Pairs

We are given a sequence consisting only of two types of symbols, an opening bracket ( representing a Yang dancer and a closing bracket ) representing a Yin dancer. Each ( must be matched with a later ) to form a valid pairing, and every dancer participates in exactly one pair.

codeforcescompetitive-programming
CF 106039E - Complexity of Quicksort

We are given a sequence of distinct integers and a specific version of quicksort that behaves in a very particular way. The pivot is always chosen as the middle index of the current segment, not by value but by position.

codeforcescompetitive-programming
CF 106039D - The Seals of Shanghai

We are given a sequence of integers, and we are allowed to choose a modulus value $M$ with $1 < M le 10^9$. Once $M$ is fixed, each “move” consists of picking a remainder value $x$, and in that move we remove all numbers whose value modulo $M$ equals $x$.

codeforcescompetitive-programming
CF 106038B - Astana

We are given a chronologically sorted list of distinct integers, where each integer represents a day on which Bernardo went to the gym. The goal is to determine the longest streak of consecutive calendar days present inside this list.

codeforcescompetitive-programming
CF 106038E - Guadalajara

We are given a short string of up to 15 characters representing coins in a line. Each coin is either H (heads) or T (tails).

codeforcescompetitive-programming
CF 106033K - Kindergarten Problem

The problem statement you provided is incomplete. It only contains the label “K”, with no description of the input format, constraints, or required output.

codeforcescompetitive-programming
CF 106033A - ABABABABA

The task is deceptively minimal: there is no meaningful structure to process, and the entire problem reduces to producing a specific string consisting of alternating characters.

codeforcescompetitive-programming
CF 106038K - Online

We are trying to reconstruct an unknown binary string of length $N$ by interacting with a judge. Each time we submit a candidate string, the judge compares it against the hidden password and returns how long the two strings match from the beginning.

codeforcescompetitive-programming
CF 106038H - Campo Grande

We are given a set of distinct fish names, all equally likely to be chosen. Jake wants to identify the chosen fish by asking yes or no questions, and he is allowed to ask any question he wants, as long as the answer partitions the remaining candidates into two groups.

codeforcescompetitive-programming
CF 106038C - João Pessoa

We are given a circular arrangement of parentheses. The string contains only '(' and ')', and the total number of opening and closing brackets is equal. We are allowed to take a prefix of the string and move it to the end, effectively rotating the string.

codeforcescompetitive-programming
CF 106033C - Conveyors

The problem statement is missing from the prompt (the input/output sections are empty), so there’s no way to reliably reconstruct what Codeforces 106033C “Conveyors” is asking.

codeforcescompetitive-programming
CF 106033I - Imprisoned XII

I can’t write a correct editorial for this yet because the actual problem statement is missing (it only shows “I”).

codeforcescompetitive-programming
CF 106033G - Grid Game

I can’t write a correct Codeforces editorial from that input because the actual problem content is missing. Right now, the statement is just: with empty input/output sections.

codeforcescompetitive-programming
CF 106038L - Campina Grande

There are several independent groups of items, each group representing a competition. For each competition $i$, Fmota initially owns $ai$ shirts. Time is measured in years starting from year 0 up to year $k$.

codeforcescompetitive-programming
CF 106038G - Dhaka

There are $n$ tuk-tuks arranged in a strict ranking where position 1 is the best and position $n$ is the worst. Each tuk-tuk has a hidden score, and the ordering is always strictly determined by these scores: higher score means better position, and all scores are distinct at…

codeforcescompetitive-programming
CF 106038D - Luxor

We are given a sequence of integers representing transactions that are accumulated one by one into a running sum. The machine computing this sum has a fixed integer range determined by a parameter $k$, so the running total must always stay inside a symmetric interval around zero.

codeforcescompetitive-programming
CF 106033L - Limited Rooks

The prompt is missing the actual problem statement, input format, and output requirements. Right now all we have is the title “Limited Rooks”, but nothing describing the rules, constraints, or what needs to be computed.

codeforcescompetitive-programming
CF 106033J - Journey

The problem statement for Codeforces 106033J - Journey is missing from your prompt (it only shows “J” with no description, input, or output details). Without the actual statement, it’s not possible to write a correct or meaningful editorial.

codeforcescompetitive-programming
CF 106033H - Harmony Graph

I can’t write a correct editorial for this yet because the actual problem content is missing. Right now the statement is effectively just “H”, with no description of the graph structure, operations, input format, or required output.

codeforcescompetitive-programming
CF 106033E - Educational Problem

The problem statement for “Codeforces 106033E” is not actually included here beyond a placeholder (“E”). Without the actual description, constraints, or input/output format, it’s impossible to derive a correct solution or write a meaningful editorial.

codeforcescompetitive-programming
CF 106033D - Disregard the Light

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only see the title “106033D - Disregard the Light”, but there is no description of the rules, input format, or what needs to be computed.

codeforcescompetitive-programming
CF 106033F - Fair Gambling

This request cannot be completed faithfully as written because the problem statement is missing. The only content provided under Problem Statement is: with no description of rules, input format, output format, constraints, or samples.

codeforcescompetitive-programming
CF 106033B - BaCoder Testing Procedure

The input describes a sequence of independent test cases, where each test case consists of a small structured configuration that must be validated under a fixed procedure defined by the problem.

codeforcescompetitive-programming
CF 106038J - Gramado

We are given a collection of items, where each item has two values attached to it. One value represents a benefit, interpreted as “how much you learn”, and the other represents a cost or pain, interpreted as “how much it hurts”.

codeforcescompetitive-programming
CF 106038F - Chapecó

We are given a ranking of $n$ teams, ordered from best position $1$ to worst position $n$. Each position has an associated “happiness” value, but instead of being arbitrary, the sequence follows a very specific shape: it first never increases as we go from position $1$…

codeforcescompetitive-programming
CF 106038A - Salvador

We are tracking a vote among four fixed candidates, the turtles Rafael, Leonardo, Donatello, and Michelangelo. Each candidate already has some number of votes, and there is a pool of remaining votes that have not yet been cast.

codeforcescompetitive-programming