brain

tamnd's digital brain — notes, problems, research

43815 notes

CF 104101C - Add 9 Zeros

We are given a collection of problems, each characterized by a single integer value that represents how many trailing zeros its difficulty scale has in a power of ten.

codeforcescompetitive-programming
CF 104101A - OP

The task is intentionally minimal. There is no input to process, no computation to perform, and no decision to make. The program is expected to produce a single fixed string on standard output.

codeforcescompetitive-programming
CF 104103A - Homework

We are given a sequence of elves arriving one by one. Each elf has a sickness threshold $si$. We also have a fixed set of dishes, each with a health value $h$ and a tastiness value $t$.

codeforcescompetitive-programming
CF 104103E - Comparing Theories

We are given two trees built on the same set of labeled leaves. Internal structure can differ between the two trees, but the leaves represent the same entities in both. The task is to compare how triples of leaves behave in the two trees.

codeforcescompetitive-programming
CF 104103D - The Name of the Fourth Problem

The core object in this problem is a self-describing integer sequence, the Golomb sequence. Each value describes how many times integers appear later, and at the same time those repetitions define the next values, which creates a recursive structure where the sequence encodes…

codeforcescompetitive-programming
CF 104103C - Password Lock

We are given a collection of integers that represent positions on a circular “password lock”, together with a modulus value $k$.

codeforcescompetitive-programming
CF 104103B - Matryoshka Inc

We are given a sequence of integers, where each integer is written in decimal form and may contain leading zeros. For every number, we are allowed to freely reorder its digits before using it.

codeforcescompetitive-programming
CF 104114J - Joyful Death

We are given a sequence of elves arriving one by one. Each elf has a sickness threshold $si$. We also have a fixed set of dishes, each with a health value $h$ and a tastiness value $t$.

codeforcescompetitive-programming
CF 104114M - Mousetrap

The input describes a tree of chambers, where each chamber initially contains some amount of cheese. A mouse starts at chamber 1 and tries to reach chamber n, which is the exit. The mouse moves in discrete steps.

codeforcescompetitive-programming
CF 104114N - Nusret Gökçe

The editorial can’t be written yet because the actual problem content is missing. Right now there is no description of what “Codeforces 104114N - Nusret Gökçe” is asking for, and the Input/Output sections are empty.

codeforcescompetitive-programming
CF 104114L - Level Up

The game consists of a sequence of realms that must be cleared in order. The player starts in realm 1 with level 1 and some initial health that we are free to choose.

codeforcescompetitive-programming
CF 104114K - Knowledge Testing Problem

We are working with a weighted undirected graph where the vertices are numbered from 1 to n. Each edge connects two vertices and has a positive cost. A key structural restriction is that every edge only connects vertices whose labels differ by at most 10.

codeforcescompetitive-programming
CF 104114H - Hanoi

We are given a stack-based puzzle involving three rods and a collection of disks with distinct sizes from 1 to n.

codeforcescompetitive-programming
CF 104114I - Inadequate Operation

We are given a sequence of nonnegative integers arranged in a line. Each operation picks two adjacent positions and replaces both values with the same number, specifically the maximum of the two values minus one, as long as that maximum is positive.

codeforcescompetitive-programming
CF 104114D - Divisible by 4 Spanning Tree

I can’t write a correct Codeforces 104120F editorial as requested because the problem statement is missing entirely (the “Problem Statement / Input / Output” sections are empty).

codeforcescompetitive-programming
CF 104114G - Gears

We are given a line of fixed axle positions, already sorted from left to right, and we must assign a given multiset of gear radii to these axles. Once placed, every neighboring pair of gears must be tangent.

codeforcescompetitive-programming
CF 104114F - Fortune over Sportsmanship

We are given a complete weighted graph on $n$ players. The weight between player $i$ and player $j$ is a symmetric value $P{i,j}$, which represents the popularity gain if those two players play a match. A match always eliminates one player.

codeforcescompetitive-programming
CF 104114E - Exercise

We are given a collection of 2n students, each with a numeric skill value. Initially, they are grouped into fixed pairs, specifically consecutive indices, so student 1 is paired with 2, student 3 with 4, and so on.

codeforcescompetitive-programming
CF 104114C - COVID

We are given a set of people and a collection of group COVID tests. Each test checks a subset of people and returns positive if at least one infected person is inside that subset.

codeforcescompetitive-programming
CF 104114B - Birthday Cake

We are given a unit square cake that contains two types of points: chocolate chips and strawberries. We are allowed to draw exactly one straight line segment that cuts through the cake.

codeforcescompetitive-programming
CF 104114A - AppendAppendAppend

We are given a base string s. Each day, Momo does not modify it internally, but instead builds a longer string by concatenating copies of the original s. After day 1, the string is exactly s. After day 2, it becomes s + s. After day k, it becomes s repeated k times in a row.

codeforcescompetitive-programming
CF 104115J - Скобка, скобка, скобка...

We are dealing with sequences formed from bracket-like operations where we build a structure step by step and are asked to compute the probability that the resulting sequence satisfies correctness conditions of a bracket system.

codeforcescompetitive-programming
CF 104115H - Халявка

We are given an $n times n$ grid where each cell must be assigned a letter from 'a' to 'z', and these letters define a priority ordering, with 'a' being the highest priority and 'z' the lowest. A robot starts at cell $(1,1)$.

codeforcescompetitive-programming
CF 104115I - Деление строки

We are given a string consisting of lowercase English letters and asked whether it can be split into exactly k contiguous non-empty pieces such that every piece contains the same number of consonant letters. A consonant here means any letter except a, e, i, o, u, y.

codeforcescompetitive-programming
CF 104115G - Дискриминант или теорема Виета?

We are given a quadratic equation with integer coefficients $a, b, c$, all of them nonzero. We are allowed to replace any subset of these three coefficients with new nonzero integers.

codeforcescompetitive-programming
CF 104115E - 21 очко

We are given a partially observed state of a standard 52-card deck and a hand of cards already taken by a player.

codeforcescompetitive-programming
CF 104115D - Xor-изация

We are maintaining an array of non-negative integers under two types of operations. The first operation applies a bitwise XOR with a given value to every element in a contiguous subarray.

codeforcescompetitive-programming
CF 104115F - Но вы обо мне слышали

There is a row of $n$ chests numbered from 1 to $n$. Exactly one chest $k$ contains treasure, while all others are empty. A pirate starts opening chests but has not yet discovered where the treasure is located.

codeforcescompetitive-programming
CF 104115B - Замощение трапециями

We are given two geometric pieces, each described as a quadrilateral with a very specific structure: a right trapezoid.

codeforcescompetitive-programming
CF 104115A - Битва за пульт

We are given a set of time intervals representing TV programs. Each program has a start time, an end time, and one of three types. Type 1 programs are preferred by Petya, type 2 by Masha, and type 3 by both of them simultaneously.

codeforcescompetitive-programming
CF 104115C - Что-то про последовательность

We start with an infinite sequence of natural numbers written in order, essentially 1, 2, 3, 4, 5 and so on. We are interested in how this sequence changes after a series of deletion operations. Each operation is defined by a step value y.

codeforcescompetitive-programming
CF 104118L - LCG Manipulation

We are given a deterministic sequence generated by a linear recurrence under a modulus. Starting from an initial value s, every next value is produced by multiplying the previous value by a, adding b, and then reducing modulo a large prime p.

codeforcescompetitive-programming
CF 104118K - Kapitan Amazing

We are given a simplified description of a keyboard where each key corresponds to an uppercase letter arranged in three rows. Some of these keys are marked with an asterisk, meaning they are “oily”, and every other key is clean.

codeforcescompetitive-programming
CF 104118I - Item Crafting

We are given a large set of items arranged in a strict dependency system. Some items are basic resources that already exist in limited quantities, while all other items are produced by recipes that consume previously defined items.

codeforcescompetitive-programming
CF 104118J - Junior Steiner Three

We are given a rectangular grid where each cell is either land or water. Exactly three cells are already land, and we are allowed to convert any number of water cells into land.

codeforcescompetitive-programming
CF 104118H - HIIT

We are given a sequence of exercises. For each exercise, Bob has three possible choices: skip it, do an easy version, or do an intense version. Each choice has an energy cost of 0, $ai$, or $bi$ respectively, with $ai < bi$.

codeforcescompetitive-programming
CF 104118D - Domination Devil

We start with a complete undirected graph on $n$ vertices, where vertex labels represent a strict ordering of “power”. Every pair of vertices is initially connected by a single edge.

codeforcescompetitive-programming
CF 104118G - Gallivanting Merchant

We are given a fixed step size $k$. We are also given $n$ time intervals, each interval representing a range of days during which a particular item is being sold. The merchant appears periodically depending on our choice of a starting day $s$.

codeforcescompetitive-programming
CF 104118F - Factions vs The Hegemon

We are given a line of n factions, each sitting in a fixed west-to-east order and each carrying a wealth value. Over time, factions disappear one by one until only a single faction remains.

codeforcescompetitive-programming
CF 104118E - Escape from Markov

We are given a weighted graph where cities are nodes and roads are undirected edges, each taking exactly one hour to traverse. From a starting city, we want the minimum time to reach a destination city. The complication is that there are patrol cars moving on fixed cyclic routes.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 38

Let $f(x_1,\dots,x_n)$ be a Boolean function, and let $G(z)$ be its generating function in the sense of Exercise 25, so that G(z)=\sum_{x\in\{0,1\}^n} f(x)\, z^{w(x)}, where $w(x)=x_1+\cdots+x_n$ is t...

taocpmathematicsalgorithmsvolume-4hard
CF 104118B - Better than Bitcoin

We are given the first $n$ prime numbers and we must split them into two groups: one for Alice and one for Bob. Each prime is indivisible and must go entirely to exactly one of them.

codeforcescompetitive-programming
CF 104118C - Conform Conforme

We are given an array of integers representing values written on students’ shirts. Each day, every position updates its value simultaneously based on a global statistic: a value v becomes the number of occurrences of v in the entire array on that day.

codeforcescompetitive-programming
CF 104118A - An Easy Calculus Problem

We are given a function $f(x)$ defined on real numbers, but split into three regions of $x$. Each region uses a different formula: a linear expression on the far left, another linear expression in the middle, and a cubic polynomial on the right.

codeforcescompetitive-programming
CF 1041193 - Престижный номер

I can’t reliably write a correct editorial for this yet because the actual problem statement for Codeforces 1041193 - “Престижный номер” is missing from your prompt.

codeforcescompetitive-programming
CF 1041195 - Олимпиада по выживанию

I can’t write a correct editorial for this problem yet because the statement is missing (the input/output description and constraints are required to derive any solution structure).

codeforcescompetitive-programming
CF 1041194 - Морской бой

I’m missing the actual problem statement for Codeforces 1041194 - “Морской бой”, so I can’t reliably reconstruct the rules or the required computation.

codeforcescompetitive-programming
CF 1041192 - Майки и носки

The problem statement section is empty, so there’s no way to reconstruct what “Майки и носки” is actually asking for. For Codeforces editorials, the solution, invariants, and even the complexity depend entirely on the task definition.

codeforcescompetitive-programming
CF 1041191 - Самолёт

I can’t write a correct editorial yet because the actual problem statement is missing. Right now I only know the title “Самолёт (Airplane)”, but there is no description of: - what the input represents, - what is being computed, - constraints, - or samples.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 37

Let $f(x_1,\dots,x_n)$ be a Boolean function, and let $G(z)$ be its generating function in the sense of Exercise 25, so that G(z)=\sum_{x\in\{0,1\}^n} f(x)\, z^{w(x)}, where $w(x)=x_1+\cdots+x_n$ is t...

taocpmathematicsalgorithmsvolume-4math-medium
CF 104120K - Keypad Repetitions

The problem statement for “Codeforces 104120K - Keypad Repetitions” is missing from your prompt, so I don’t have enough information to write a correct editorial.

codeforcescompetitive-programming
CF 104120L - Ladybug And The Bullet Train

The problem statement section is empty, so there isn’t enough information to write a correct editorial. For a Codeforces editorial, I need at least the full description of what “Ladybug And The Bullet Train” is asking: the input format, what is being simulated or computed…

codeforcescompetitive-programming
CF 104120J - Joyful City

We are given a tree with n cities connected by n − 1 undirected roads. Every road must be assigned a direction, turning the undirected tree into a directed structure where each edge becomes a one-way connection.

codeforcescompetitive-programming
CF 104120I - Ivan And Mega Queries

I don’t have the actual statement for Codeforces 104120I - Ivan And Mega Queries in your message, so I can’t reliably reconstruct the problem or produce a correct editorial without guessing.

codeforcescompetitive-programming
CF 104120F - Fence Painting

I can’t write a correct Codeforces 104120F editorial as requested because the problem statement is missing entirely (the “Problem Statement / Input / Output” sections are empty).

codeforcescompetitive-programming
CF 104120G - Hola

The problem statement is missing from your prompt, so I don’t have enough information to write a correct editorial for Codeforces 104120G - Hola.

codeforcescompetitive-programming
CF 104120H - Homework

I can’t write a correct editorial for this yet because the actual problem statement for Codeforces 104120H - Homework is missing from your prompt.

codeforcescompetitive-programming
CF 104120E - Exam Period

I can write the full Codeforces-style editorial, but I’m missing the actual problem content for 104120E - Exam Period (statement, input, output, constraints).

codeforcescompetitive-programming
CF 104120D - Denji1

The problem content is missing from the prompt. Right now, only the title “Codeforces 104120D - Denji1” is provided, but the actual statement, constraints, input/output format, and samples are empty.

codeforcescompetitive-programming
CF 104120A - Average Walk

Connection interrupted. Waiting for the complete answer

codeforcescompetitive-programming
CF 104120B - Business Stamps

I can write the full editorial in exactly that style, but I’m missing the actual problem statement for Codeforces 104120B - Business Stamps.

codeforcescompetitive-programming
CF 104120C - Company Layoffs

The prompt is missing the actual problem statement for “Codeforces 104120C - Company Layoffs”, so there isn’t enough information to reconstruct the model, constraints, or intended solution.

codeforcescompetitive-programming
CF 104128K - NaN in a Heap

Let $h{a,b}(x)=((ax+b)gg(n-l)) bmod 2^l$, with $ain A={amid 0<a<2^n, a text{odd}}$ and $bin B={bmid 0le b<2^{n-l}}$. For fixed sets $P$ and $Q$ of $n$-bit integers, define $$I={h{a,b}(p)mid pin P},qquad J={h{a,b}(q)mid qin Q}.$$ Let $ $$Pr[h{a,b}(x)=h{a,b}(y)]le 2^{-l}.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 36

Exercise 31 provides a method for evaluating a BDD by interpreting each sink and branch node as an element of an algebraic system equipped with operations $\circ$ and $\bullet$, and propagating values...

taocpmathematicsalgorithmsvolume-4medium
CF 104128M - Drain the Water Tank

The problem statement is missing from your message, so there’s no way to reliably reconstruct the model, constraints, or required algorithm.

codeforcescompetitive-programming
CF 104128L - Proposition Composition

I can’t reliably write a correct editorial for “Codeforces 104128L - Proposition Composition” without the actual problem statement.

codeforcescompetitive-programming
CF 104128J - Perfect Matching

I can write the full editorial in the exact style you requested, but I’m missing the only thing needed to make it correct: the actual problem statement for Codeforces 104128J - Perfect Matching.

codeforcescompetitive-programming
CF 104128I - Perfect Palindrome

I can’t write a correct editorial for “Codeforces 104128I - Perfect Palindrome” as-is because the actual problem statement is missing from your prompt. Right now I don’t know: - what the input structure is (string, array, multiple test cases, etc.

codeforcescompetitive-programming
CF 104128A - Stop, Yesterday Please No More

Let $h{a,b}(x)=((ax+b)gg(n-l)) bmod 2^l$, with $ain A={amid 0<a<2^n, a text{odd}}$ and $bin B={bmid 0le b<2^{n-l}}$. For fixed sets $P$ and $Q$ of $n$-bit integers, define $$I={h{a,b}(p)mid pin P},qquad J={h{a,b}(q)mid qin Q}.$$ Let $ $$Pr[h{a,b}(x)=h{a,b}(y)]le 2^{-l}.

codeforcescompetitive-programming
CF 104128H - Factories Once More

I can’t write a correct editorial for “Codeforces 104128H - Factories Once More” because the problem statement is missing from your prompt. Right now there’s no information about: - what the “factories” are in the model (graph, array, tree, etc.

codeforcescompetitive-programming
CF 104128G - Inscryption

I can’t reliably write a correct editorial for Codeforces 104128G - Inscryption from just the title. The full solution depends entirely on the actual rules (game mechanics, operations allowed, constraints, and what is being optimized or decided).

codeforcescompetitive-programming
CF 104128F - Triangles

The problem statement for “Codeforces 104128F - Triangles” is not included in your message, so I don’t have the actual definitions of the input, output, or the task the solution is supposed to solve.

codeforcescompetitive-programming
CF 104128E - Color the Tree

I can’t reliably write a correct editorial for this without the actual problem statement. “Codeforces 104128E - Color the Tree” isn’t identifiable from the title alone, and guessing would very likely produce the wrong model, wrong constraints, and therefore a misleading…

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 35

Let $G$ be the given FBDD with node set $V(G)$.

taocpmathematicsalgorithmsvolume-4medium
CF 104128D - Chat Program

I can’t write a correct editorial yet because the actual problem statement for “Codeforces 104128D - Chat Program” is missing from your prompt.

codeforcescompetitive-programming
CF 104128C - Fabulous Fungus Frenzy

I can’t reliably write a correct Codeforces editorial for “104128C - Fabulous Fungus Frenzy” because the actual problem statement, input format, and constraints are missing from your prompt.

codeforcescompetitive-programming
CF 104128B - Ropeway

I’m missing the actual problem statement for Codeforces 104128B - Ropeway, and without it I can’t produce a correct editorial.

codeforcescompetitive-programming
CF 104135I - НОД и подмножества

The statement for Codeforces 104135I (“НОД и подмножества”) is not included in your message, so I don’t have enough information to reconstruct the task reliably.

codeforcescompetitive-programming
CF 104135H - Сложная матрица

I can’t write a correct editorial for this yet because the actual problem statement is missing from your prompt. Right now I only see the title “Сложная матрица” and no description of what the matrix operations or required output are.

codeforcescompetitive-programming
CF 104135B - Крош и битовые операции

Let $h{a,b}(x)=((ax+b)gg(n-l)) bmod 2^l$, with $ain A={amid 0<a<2^n, a text{odd}}$ and $bin B={bmid 0le b<2^{n-l}}$. For fixed sets $P$ and $Q$ of $n$-bit integers, define $$I={h{a,b}(p)mid pin P},qquad J={h{a,b}(q)mid qin Q}.$$ Let $ $$Pr[h{a,b}(x)=h{a,b}(y)]le 2^{-l}.

codeforcescompetitive-programming
CF 104135G - Задача о перестановках

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only see the title “Codeforces 104135G - Задача о перестановках”, but no description of what is given, what needs to be computed, or the…

codeforcescompetitive-programming
CF 104135F - Крош и интересные пары чисел

I can’t write a correct editorial yet because the actual statement of Codeforces 104135F - “Крош и интересные пары чисел” is not included in your prompt, and it is not available in a clean form from the metadata we currently have.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 34

Let $B$ be the BDD of $f(x_1,\dots,x_n)$ with root node $r$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 104135E - Крош и строка

The problem statement section is empty, so there is no way to reconstruct what “Крош и строка” is actually asking. Any attempt to write a full editorial without the task definition would be guesswork and would likely produce a completely incorrect solution.

codeforcescompetitive-programming
CF 104135C - Крош и удаления

We are given a sequence of numbers representing a row of elements, each element having two attributes: a value and a removal cost. The game allows us to repeatedly pick two adjacent elements and delete the smaller-valued one, paying its associated removal cost.

codeforcescompetitive-programming
CF 104135D - Дождь

I can’t reliably write a correct editorial for Codeforces 104135D - “Дождь” without the actual problem statement. Right now I only have the title, but no description of what the input/output represents or what the task is asking.

codeforcescompetitive-programming
CF 104135A - Крош и пароль

The problem statement for Codeforces 104135A - “Крош и пароль” is missing from your prompt, so there’s no reliable way to reconstruct the solution or write a correct editorial without guessing.

codeforcescompetitive-programming
CF 104142K - Пора домой!

We are given an undirected graph where each vertex is a named place inside a university building. Some of these places are special: the starting point is deansoffice, the destination is street, and there is exactly one additional mandatory place, the room where the student’s…

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 33

Let the BDD represent $f(x_1,\dots,x_n)$ with variable order $x_1 < x_2 < \cdots < x_n$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 104142J - Плоские фигуры

I can’t reliably reconstruct Codeforces 104142J (“Плоские фигуры”) from the title alone, and writing a correct editorial without the actual statement would risk inventing constraints, rules, or even the task itself.

codeforcescompetitive-programming
CF 104142I - WA 132

The problem statement is missing from your prompt, so there is no way to reconstruct the task, constraints, or intended solution for “Codeforces 104142I - WA 132”. An editorial depends entirely on knowing what the input represents and what needs to be computed.

codeforcescompetitive-programming
CF 104142H - Сбалансированные деревья

I can’t write a correct editorial for this without the actual problem statement. Right now the only thing available is the title, but “Сбалансированные деревья” (Balanced Trees) could correspond to multiple different tasks, and the required data…

codeforcescompetitive-programming
CF 104142G - Камень, ножницы, бумага

The problem statement is missing from your prompt (both the input and output sections are empty), so there isn’t enough information to write a correct Codeforces editorial.

codeforcescompetitive-programming
CF 104142E - Квадраты

I can’t write a correct editorial for this problem yet because the actual problem statement is missing from your message. “Codeforces 104142E - Квадраты” alone isn’t enough to reconstruct the task reliably.

codeforcescompetitive-programming
CF 104142F - Забор

I can’t write a correct Codeforces editorial for this problem yet because the actual problem statement is missing. Right now I only have the title “104142F - Забор”, but no description of what the input represents, what needs to be computed, or even the constraints.

codeforcescompetitive-programming
CF 104142D - Пляж

The statement content is missing in the prompt, so there isn’t enough information to reconstruct Codeforces 104142D (Пляж) reliably.

codeforcescompetitive-programming
CF 104142B - Шифр

I can write the full editorial in exactly that format, but I’m missing the actual problem statement for Codeforces 104142B - Шифр.

codeforcescompetitive-programming
CF 104142A - Hello, world!

This problem strips away all structure and asks for a fixed output regardless of the input. You are given some input stream, which may contain anything, but none of it influences the required result. The task is simply to produce a single exact string as the program’s output.

codeforcescompetitive-programming
CF 104142C - Окружности

I can’t write a correct editorial for this yet because the actual problem statement is missing. “Codeforces 104142C - Окружности” is a geometry problem (circles), but without the exact rules, input format, and required output, any solution would be guesswork.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 32

Exercise 31 describes a generic BDD evaluation scheme in which a function is computed by replacing each internal decision node labeled by variable $x_j$ with an algebraic combination of the values of...

taocpmathematicsalgorithmsvolume-4math-medium