brain

tamnd's digital brain — notes, problems, research

43815 notes

CF 104146M - Mondriamorsolo

We are asked to construct a very structured tiling of an $n times n$ grid using exactly $n$ rectangular regions. Each region is filled with a single letter, so visually each rectangle becomes a monochromatic block in the grid.

codeforcescompetitive-programming
CF 104146K - Kyuu Sort

We are given a queue of $n$ distinct integers representing a permutation. Each value is a ranking, and the goal is to transform the queue into increasing order so that the smallest rank ends up at the front and the largest at the back.

codeforcescompetitive-programming
CF 104146L - Legends: Are You Serious?

We are given a grid world where each cell is either normal ground, lava, or mud. Cindy starts at a fixed cell, initially facing south, and must reach a target cell.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 31

Let $f(x_1,\dots,x_n)$ be represented by an ordered reduced BDD with root node $r$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 104146J - Jumpin' Jack Flash

We are given three distinct points in the plane with integer coordinates, and we are asked to reason about all possible ways to complete them into a parallelogram by choosing a fourth vertex.

codeforcescompetitive-programming
CF 104146I - Image of the Artist as Filipino

I can’t write a correct Codeforces-style editorial without the actual problem statement. “Codeforces 104146I - Image of the Artist as Filipino” is not available in the prompt, and I don’t have the input/output description, constraints, or even the core task (graph, DP…

codeforcescompetitive-programming
CF 104146H - Harvest Moon Rabbits

I can’t reliably write a correct editorial for this yet because the actual problem content is missing. Right now the “Problem Statement / Input / Output” sections are empty, so there’s no way to know what Codeforces 104146H - Harvest Moon Rabbits is asking, what the…

codeforcescompetitive-programming
CF 104146G - Good as Gold

I can’t reliably write a correct editorial for Codeforces 104146G - Good as Gold because the problem statement is missing from your prompt. Right now, I only see the template sections (Input/Output are empty), so any attempt to reconstruct the problem would be guesswork.

codeforcescompetitive-programming
CF 104146F - Four Warning

I can’t write a correct editorial for CF 104146F - Four Warning without the actual problem statement. Right now you’ve only provided the title and metadata, but the solution structure, key observations, and even what the input/output represent all depend entirely on the…

codeforcescompetitive-programming
CF 104146E - Experiment - Anubis Edition!

The problem statement section is empty, so there isn’t enough information to write a correct editorial for Codeforces 104146E.

codeforcescompetitive-programming
CF 104146D - Digital Style!

I can’t reliably write a correct editorial for “Codeforces 104146D - Digital Style!” because the actual problem statement (inputs, outputs, and rules) is missing from your prompt.

codeforcescompetitive-programming
CF 104146B - Braid

We are given a visual construction problem: instead of computing a numeric answer, we must simulate and print how a three-strand braid evolves over time using ASCII art. At the start, there are three vertical strands, each labeled by a distinct character from a given string.

codeforcescompetitive-programming
CF 104146A - ABCs of Men and Women

We are given a short string that represents a faded name tag. The original name is known to be exactly one of three fixed strings: Alice, Bob, or Cindy. However, the observed string may contain lowercase or uppercase letters, and some positions may be unreadable, shown as a dot.

codeforcescompetitive-programming
CF 104146C - Codemas Carols

I can’t write a correct editorial for “Codeforces 104146C - Codemas Carols” without the actual problem statement. Right now the input/output sections are empty, so anything I write would be guesswork and would likely invent the wrong problem entirely.

codeforcescompetitive-programming
CF 104147K - Hobz is a good guy

We are given a binary string and we are allowed to delete any number of characters from it, possibly all but at least one character must remain.

codeforcescompetitive-programming
CF 104147J - Two Faced Hobz

Each test case gives a collection of $N$ independent pairs. From the $i$-th pair you must choose exactly one value, either $Ai$ or $Bi$. After all choices are made, all selected values are XORed together to produce a single number, called the Salkan.

codeforcescompetitive-programming
CF 104147I - Wigz

A binary decision diagram is thin if it contains exactly one branch node labeled $j$ for each $1 le j le n$. Denote by $Sn$ the number of Boolean functions on $(x1,dots,xn)$ whose reduced ordered BDD is thin. Let $vj$ denote the unique node labeled $j$.

codeforcescompetitive-programming
CF 104147G - You're Milky

We are simulating a process where a person receives multiple deliveries of milk over time. Each delivery arrives on a specific day with a given quantity. Milk is not permanent: every batch has a fixed freshness window, after which it becomes unusable and must be discarded.

codeforcescompetitive-programming
CF 104147H - Alexandria Library

The problem statement section is empty, so there’s no way to reconstruct the actual task reliably. For a Codeforces editorial, the difference between a graph problem, a data structure problem, or a combinatorics problem completely changes the approach, so guessing would…

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 30

Let the contribution of a minterm corresponding to an assignment $x_1 \ldots x_n$ be C(x_1,\ldots,x_n)=\prod_{i=1}^n (1-p_i)^{1-x_i}p_i^{x_i}.

taocpmathematicsalgorithmsvolume-4math-medium
CF 104147F - Nesr El Sieve

I don’t have the actual problem statement for Codeforces 104147F - Nesr El Sieve, so I can’t safely reconstruct the solution or write a correct editorial yet.

codeforcescompetitive-programming
CF 104147D - Do and Tak Game

I can’t reliably write a correct editorial for “Codeforces 104147D - Do and Tak Game” because the problem statement is missing from your prompt, and I don’t have enough information to reconstruct the rules, constraints, or required output.

codeforcescompetitive-programming
CF 104147E - I am not done yet

I don’t have the actual statement for Codeforces 104147E - I am not done yet in your prompt, so I can’t reconstruct the problem, constraints, or intended solution without risking inventing details.

codeforcescompetitive-programming
CF 104147C - Disney Land

I don’t have the actual statement of Codeforces 104147C - Disney Land in the prompt, and I can’t reliably reconstruct it from the title alone without risking inventing details.

codeforcescompetitive-programming
CF 104147B - I'll call him Hanya

I can’t reliably write a correct editorial without the actual problem statement for Codeforces 104147B (“I’ll call him Hanya”).

codeforcescompetitive-programming
CF 104147A - Round 1

I can write the full editorial in the format you want, but I’m missing the actual problem statement for Codeforces 104147A - Round 1.

codeforcescompetitive-programming
CF 104148D - Кубическая непрерывность

I’m missing the actual problem statement, so I can’t safely reconstruct the intended solution or write a correct editorial for it.

codeforcescompetitive-programming
CF 104148C - Продуктовый магазин

We are dealing with a shop that sells multiple products, where each product type may have a required number of units that must be purchased.

codeforcescompetitive-programming
CF 104148A - Сколько чисел

The problem statement is missing from the prompt, so there is no reliable way to reconstruct what Codeforces 104148A (“Сколько чисел”) is asking.

codeforcescompetitive-programming
CF 104148B - Уникальный комикс

I don’t have the actual statement for Codeforces 104148B “Уникальный комикс”, and without it I can’t reliably reconstruct the intended algorithm or constraints.

codeforcescompetitive-programming
CF 104149M - Magic Marbles

We maintain a sequence of colored marbles. Initially there is a fixed list of colors, and then we process a stream of operations. Each operation inserts a single marble at a specified position in the current sequence.

codeforcescompetitive-programming
CF 104149K - Kettle Kitten

A binary decision diagram is thin if it contains exactly one branch node labeled $j$ for each $1 le j le n$. Denote by $Sn$ the number of Boolean functions on $(x1,dots,xn)$ whose reduced ordered BDD is thin. Let $vj$ denote the unique node labeled $j$.

codeforcescompetitive-programming
CF 104149J - Joint Jinx

We are asked to construct a configuration of $n$ circles in the plane such that the total number of distinct intersection points between circles is exactly $k$.

codeforcescompetitive-programming
CF 104149L - Longbottom Leap

We are given a binary string that represents a long staircase. Each character corresponds to a step, and only the positions marked with 1 are broken and need to be fixed.

codeforcescompetitive-programming
CF 104149I - Inconspicuous Identity

We are modeling an umbrella whose shape is determined by a central point at the top and eight identical rigid ribs of fixed length. Fabric is stretched between adjacent ribs, forming eight identical triangular panels arranged around the center.

codeforcescompetitive-programming
CF 104149H - Hidden Horcrux

Harry is trying to reach a desert center that is exactly $d$ days away if he walks alone. Every day consumes one unit of water per person.

codeforcescompetitive-programming
CF 104149G - Going for Gold

We are given a tournament with n competitors, each representing a school champion. For every competitor, we already know their ranking in the first two events. A lower rank is better, and all ranks in each event form a permutation of 1 through n.

codeforcescompetitive-programming
CF 104149F - Forming Friendships

We are given a set of students and a list of friendships between them. Each friendship is undirected. The key twist is that a magical process will run: whenever student A is friends with B, and B is friends with C, the spell forces A and C to become friends as well.

codeforcescompetitive-programming
CF 104149E - Enchanted Exam

We are trying to identify an unknown integer $x$ in the range from 1 to 100. The only way to gain information about $x$ is by asking queries: we choose an integer $y$ in the same range and receive one of four possible responses depending on the relationship between $y$ and $x$.

codeforcescompetitive-programming
CF 104149D - Document Dimensions

We are given a sequence of words that must be written on paper in lines. Each word has a length in characters, and if two words appear on the same line they must be separated by exactly one space.

codeforcescompetitive-programming
CF 104149B - Basic Brewing

We are given several cauldrons of potion. Each cauldron contains a known number of liters and each liter has a known concentration of an ingredient.

codeforcescompetitive-programming
CF 104149C - Cellar Chase

The dungeon is described as a system built from a few primitive corridors that are then combined repeatedly. Each primitive corridor connects an entrance to an exit and behaves like a single undirected passage from one endpoint to another.

codeforcescompetitive-programming
CF 104149A - Alohomora and Colloportus

We are given a set of n objects, each representing a chain link. Some pairs of links are already connected, forming an undirected simple graph.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 29

Let $f$ be represented by a reduced ordered binary decision diagram, and let $F(p)$ denote the reliability polynomial under the specialization $p_1=\cdots=p_n=p$.

taocpmathematicsalgorithmsvolume-4hm-medium
CF 104150D - Преступная сеть

I can write the full editorial in exactly the format you want, but I don’t have the actual statement of Codeforces 104150D (“Преступная сеть”) available in this context, and I shouldn’t guess it because that would produce a misleading solution.

codeforcescompetitive-programming
CF 104150A - Допрос подозреваемых

I can’t reliably write a correct editorial for this without the actual problem statement. “Codeforces 104150A - Допрос подозреваемых” (Interrogation of suspects) isn’t enough to reconstruct the task, and guessing would almost certainly produce a wrong…

codeforcescompetitive-programming
CF 104150B - Исследование улик

I’m missing the actual problem statement for Codeforces 104150B (“Исследование улик”). Without knowing what the input represents or what is being computed, I can’t reliably reconstruct the intended solution, and anything I write would risk being incorrect…

codeforcescompetitive-programming
CF 104150C - Зашифрованное сообщение

I can’t reliably reconstruct Codeforces 104150C (“Зашифрованное сообщение”) from the identifier alone, and the problem statement isn’t included in your prompt.

codeforcescompetitive-programming
CF 1041554 - Разноцветные точки

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

codeforcescompetitive-programming
CF 1041553 - Робот-пылесос

We are given a square-shaped robot with fixed side length k placed on a 2D plane. The robot starts at a known position and then moves in a sequence of straight-line segments.

codeforcescompetitive-programming
CF 1041551 - Разделение прямоугольника

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

codeforcescompetitive-programming
CF 1041552 - Произведение Фибоначчи

I cannot reliably reconstruct the full official statement of “Codeforces 1041552 - Произведение Фибоначчи” from the title alone, and the exact input/output format is essential for a correct editorial.

codeforcescompetitive-programming
CF 1041568 - Обыкновенная задача про строки

We are given multiple queries, and each query is a string over the alphabet {a, b, c}. Two strings are considered equivalent if they “look the same” when you only observe how pairs of consecutive characters behave.

codeforcescompetitive-programming
CF 1041565 - Метрострой

We are given a system of $n$ engines that all receive the same control parameter $x$, which we can think of as a global voltage. Each engine reacts to this voltage in a piecewise linear way. Every engine $i$ has a threshold $zi$.

codeforcescompetitive-programming
CF 1041566 - Красивые последовательности

I don’t have the actual statement for Codeforces 1041566 “Красивые последовательности” in the prompt, so I can’t reliably reconstruct the problem, constraints, or intended solution.

codeforcescompetitive-programming
CF 1041567 - Камни

I can’t reliably write a correct Codeforces editorial without the actual problem statement for “1041567 - Камни”.

codeforcescompetitive-programming
CF 104157I - Drunk Coworker

A quadratic curve describes how a drunk coworker walks across a rectangular office. At any horizontal position $x$, his position is $f(x)$, so his path is a parabola. He cannot see infinitely precisely.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 28

Let $f(x_1,\ldots,x_n)$ be a Boolean function and let G(z)=\sum_{x_1=0}^1 \cdots \sum_{x_n=0}^1 z^{x_1+\cdots+x_n} f(x_1,\ldots,x_n) be its generating function as defined in the preceding exercise.

taocpmathematicsalgorithmsvolume-4math-medium
CF 104157H - Crapper's Collapse Catastrophe

The building can be seen as a rooted structure where room numbers represent nodes in a very large implicit tree. Room 0 is the root. Every room belongs to a floor, and the structure alternates branching rules depending on whether the floor index is even or odd.

codeforcescompetitive-programming
CF 104157G - Crappy Typing

We are given a sequence of employees standing in a fixed order, where each employee has a known typing duration. There are M identical computers, and these computers act like parallel processors that continuously take the next available person in the queue.

codeforcescompetitive-programming
CF 104157F - Toilet Orders

We are given two large integers per test case, representing available counts of two complementary parts. From these counts, Thomas effectively produces a number of complete pairs equal to the greatest common divisor of the two values.

codeforcescompetitive-programming
CF 104157E - Brainless Brainstorming

We are given a sequence of $N$ time slots. In each slot $i$, there are three employees, and each employee would contribute a known number of ideas if invited during that slot. However, Michael has two restrictions that interact in a nontrivial way.

codeforcescompetitive-programming
CF 104157D - Speedy Stamping

We are given a target string consisting only of the characters T and C. We want to count how many different ways an employee can produce this exact string using a fixed set of stamps.

codeforcescompetitive-programming
CF 104157C - Flush-tastic Throwing Challenge

We are given a circular target on a 2D plane and a list of points representing where different employees threw an object. The task is to count how many of these thrown points land inside the circle or exactly on its boundary. Each throw is just a coordinate pair.

codeforcescompetitive-programming
CF 104157A - Printing Papers

We are given a weekly supply limit, and Michael is allowed to make exactly one purchase. The restriction is that the quantity he buys must be a power of two. Among all valid purchase amounts that do not exceed the available supply, we need to choose the largest one.

codeforcescompetitive-programming
CF 104157B - Watch Your Sugar!

We are given a collection of chocolates, each with a known amount of sugar. Thomas has a daily sugar limit and wants to eat as many whole chocolates as possible without the total sugar exceeding that limit.

codeforcescompetitive-programming
CF 104158K - Office Odyssey

We are given an undirected tree with $n$ nodes, representing office buildings connected by $n-1$ hallways. On this tree, there are $m$ ordered pairs of nodes, and each pair defines a journey that follows the unique simple path between its endpoints.

codeforcescompetitive-programming
CF 104158J - High Jump

We are given a line of tiles, initially each tile has height 1. Over time, the heights only increase. Each operation selects a contiguous segment and adds the same value to every tile in that segment.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 27

Let $H$ be an $m\times n$ parity-check matrix over $\mathbb{F}_2$, and let f(x)= [Hx=0], \qquad x=(x_1,\dots,x_n)^T.

taocpmathematicsalgorithmsvolume-4math-hard
CF 104158I - Drunk Coworker

We are given a quadratic curve that models a drunk coworker’s path across a rectangular room. At any horizontal position $x$, the coworker is located at height $f(x)$, where $f$ is a quadratic function.

codeforcescompetitive-programming
CF 104158H - Crapper's Collapse Catastrophe

We can think of the building as an infinite rooted structure starting from room 0. Each room generates new rooms in the level above it, but the branching factor depends on the parity of the room: even-indexed rooms expand into a rooms, and odd-indexed rooms expand into b rooms.

codeforcescompetitive-programming
CF 104158F - Toilet Orders

We are given pairs of large integers representing counts of two types of parts, bowls and lids. From each pair, the number of complete toilets Thomas can assemble is determined by the greatest common divisor of these two quantities.

codeforcescompetitive-programming
CF 104158G - Crappy Typing

We are given a queue of employees, each associated with a fixed typing duration. There are $N$ employees standing in order, and we can place $M$ computers in front of them. At time zero, the first $M$ employees each occupy one computer and start typing.

codeforcescompetitive-programming
CF 104158E - Brainless Brainstorming

We are given a sequence of $N$ time slots, each slot containing three independent offers: one from Jim, one from Dwight, and one from Kevin. In slot $i$, choosing Jim yields $ai$ ideas, Dwight yields $bi$, and Kevin yields $ci$.

codeforcescompetitive-programming
CF 104158D - Speedy Stamping

We are given a target string consisting only of the characters T and C. The task is to count how many different ways this string can be formed using a fixed set of stamps. Each position in the string is produced by choosing one of four stamp types.

codeforcescompetitive-programming
CF 104158C - Flush-tastic Throwing Challenge

We are given a circular target on a 2D plane and a set of points representing where employees throw an object. The task is to count how many of these points land inside or exactly on the boundary of the circle. Each throw is just a coordinate on the plane.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 267

Let $U=\{1,\dots,n\}$ with variable order $1<2<\cdots<n$.

taocpmathematicsalgorithmsvolume-4hm-hard
CF 104159H - Непростые отношения между числами

We are given a prefix of natural numbers from 1 up to some limit $n$, and we want to choose as many of them as possible under a single restriction.

codeforcescompetitive-programming
CF 104159G - Погоня, погоня, погоня

Two trucks move along a straight road made of five consecutive segments. Each segment has a fixed length, and two of these segments are “bad road” segments where movement becomes slower for both vehicles.

codeforcescompetitive-programming
CF 104159F - Wordland

We are given several short strings made of lowercase English letters. For each string, we need to decide whether it is “valid” under a rule that depends on how letters alternate between two classes: vowels and consonants. The rule is applied after a preprocessing step.

codeforcescompetitive-programming
CF 104159E - Верстовые столбы

We are given a positive integer $N$. We need to construct the smallest positive integer that satisfies two conditions at the same time: it must be divisible by $N$, and its decimal representation must end in the digit zero. Ending in zero means the number is a multiple of 10.

codeforcescompetitive-programming
CF 104160M - Vulpecula

We are given a tree of up to $n$ vertices, where each vertex represents a star. The tree is rooted implicitly by the input construction, but conceptually it is just an undirected tree defined by $n-1$ edges. For each star, Mu chooses it as a viewing center.

codeforcescompetitive-programming
CF 104160L - Tavern Chess

Two players build small combat teams, each consisting of at most seven units placed in a fixed left-to-right order. Every unit starts with a single attribute value, which simultaneously acts as its hit points and its attack power.

codeforcescompetitive-programming
CF 104160K - Security at Museums

We are given a simple polygon described by its vertices in counterclockwise order. On each vertex sits an object, and we want to count how many subsets of these vertices a group of thieves could choose, under a strong geometric constraint.

codeforcescompetitive-programming
CF 104160J - Referee Without Red

We are given an $n times m$ grid where each cell contains a species label. The grid represents a rigid matrix formation of dancers. The only way the configuration can change is through operations triggered by showing cards. A white card labeled $k$ affects row $k$.

codeforcescompetitive-programming
CF 104160I - Quartz Collection

We are given $n$ quartz types, and each type has two prices: a first piece price and a second piece price. Every type has exactly two pieces, but the second piece only becomes available after the first one of that type has been bought.

codeforcescompetitive-programming
CF 104160G - Meet in the Middle

We are given two independent weighted networks on the same set of cities. One network consists of roads and the other consists of railways.

codeforcescompetitive-programming
CF 104160H - P-P-Palindrome

We are given a collection of strings. From all substrings of all these strings, we are interested only in those substrings that are palindromes. Each such palindrome can be used as a building block.

codeforcescompetitive-programming
CF 104160E - Graph Completing

We start with a connected simple undirected graph. We are allowed to insert any number of missing edges, as long as we never introduce self-loops or duplicate edges. Every different subset of edges that we choose to add counts as a different construction.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 266

Let $F$ be a forest on $\{1,\dots,n\}$ whose vertices are labeled in preorder, and let a(F)=\{\operatorname{anc}(1),\dots,\operatorname{anc}(n)\}.

taocpmathematicsalgorithmsvolume-4medium
CF 104160F - Half Mixed

We are asked to fill an $n times m$ binary matrix, each cell being either 0 or 1, and then consider every subrectangle formed by choosing a contiguous block of rows and a contiguous block of columns.

codeforcescompetitive-programming
CF 104160D - DRX vs. T1

We are given a fixed-length sequence of 5 characters describing the outcomes of a best-of-five series between DRX and T1.

codeforcescompetitive-programming
CF 104160C - Clamped Sequence

We are given a sequence of numbers and asked to apply a single global “compression” operation defined by an interval $[l, r]$, where the interval length is limited by $r - l le d$.

codeforcescompetitive-programming
CF 104160A - Absolute Difference

We are given two players, Alice and Bob. Each of them does not pick from a discrete list, but from a continuous set of real numbers. Their allowed numbers are described as a union of several disjoint closed intervals.

codeforcescompetitive-programming
CF 104160B - Binary Substrings

We are given a length $n$, and we must construct a binary string of that length. The goal is not to satisfy any pattern constraint, but to maximize how many distinct nonempty substrings appear in the string.

codeforcescompetitive-programming
CF 104162I - Гладкие числа

I’m missing the actual problem statement for Codeforces 104162I - “Гладкие числа”, and without it I can’t produce a correct editorial.

codeforcescompetitive-programming
CF 104162F - Австралийская ПСП

We are given a string consisting of multiple types of brackets, specifically parentheses, square brackets, braces, and angle brackets. The interpretation of “correctness” here is not the standard single-pair matching rule used in classical bracket problems.

codeforcescompetitive-programming
CF 104162H - Выращивание кроликов

The problem statement for “Codeforces 104162H - Выращивание кроликов” is missing from your prompt, so there’s no way to reconstruct the solution logic, constraints, or intended algorithm correctly.

codeforcescompetitive-programming
CF 104162G - Очередная скобочная последовательность

I can’t reliably write a correct editorial for this yet because the actual problem statement for Codeforces 104162G - “Очередная скобочная последовательность” is missing from your prompt.

codeforcescompetitive-programming
CF 104162E - Грибные пары

We are given a sequence of mushrooms placed along a line, each with an initial weight. From this initial configuration, pairs of adjacent mushrooms can interact in a deterministic way: every unit of time, between any two neighboring mushrooms, a new mushroom appears whose…

codeforcescompetitive-programming