brain

tamnd's digital brain — notes, problems, research

41638 notes

CF 105862A - Dragons

We are given a simple progression simulation involving a character and a sequence of dragons. Each dragon has a required strength to be defeated and a reward in strength after being defeated. The character starts with an initial strength value.

codeforcescompetitive-programming
CF 105862B - Fair and Square

The problem asks us to take a rectangular grid with height n and width m, make several identical copies of it, and attach those copies without rotating them. The final combined shape must be a square. We need the smallest number of copies needed to achieve that.

codeforcescompetitive-programming
CF 105862C - Women and Cars

I can absolutely write that kind of editorial, but I’m missing the one thing needed to make it correct: the actual problem statement.

codeforcescompetitive-programming
CF 105873L - La Vaca Saturno Saturnita vs Tung Tung Tung Sahur

Analyzing

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 12

The previous solution failed because it replaced scheme (13) with an abstract left-fold instead of deriving the evaluation order actually defined in TAOCP.

taocpmathematicsalgorithmsvolume-4simple
TAOCP 7.1.2 Exercise 11

The previous solution fails because it silently turned $U(f)$ into an exact-length function by assuming global optimality of decompositions.

taocpmathematicsalgorithmsvolume-4medium
CF 105873K - Killable Demon

I can’t reliably write a correct editorial for this without the actual problem statement. “Codeforces 105873K - Killable Demon” isn’t something I can reconstruct from title alone, and inventing details would defeat the purpose of a Codeforces editorial.

codeforcescompetitive-programming
CF 105873J - JuPaels Palindrome

I can write the full Codeforces-style editorial, but I’m missing the actual problem statement content for 105873J - JuPaels Palindrome (the Input/Output section is empty in what you provided).

codeforcescompetitive-programming
CF 105873I - ICPC Challenge

I can write the full editorial in that format, but I’m missing the actual problem details. The identifier “Codeforces 105873I - ICPC Challenge” is not enough for me to reliably reconstruct the statement, constraints, samples, and intended algorithm, and I don’t want to…

codeforcescompetitive-programming
CF 105873H - Huron Designs

We are given a collection of independent jobs. Each job represents a design request that Tony can either accept or ignore.

codeforcescompetitive-programming
CF 105873G - Generating Polygons

We are asked to construct a simple polygon with exactly $n$ vertices, each vertex placed at integer coordinates, such that the polygon has a prescribed area $A$.

codeforcescompetitive-programming
CF 105873F - First Problem

We maintain a sequence of numbers. Initially every position has a given value, and then we process a stream of operations. A query asks for the maximum value inside a chosen interval. An add operation increases every value in an interval by one.

codeforcescompetitive-programming
CF 105873E - Elisas Boxes

We are given a row of boxes, each box having a fixed capacity. Alongside, there is a number representing how many identical artifacts Elisa wants to place inside a single box.

codeforcescompetitive-programming
CF 105873D - Delivering Orders

I can absolutely write that kind of full Codeforces-style editorial, but I’m missing the actual problem content.

codeforcescompetitive-programming
CF 105873C - Celayas New Sign

In this problem, we have two strings. The first one is the text currently printed on the sign, and the second one is the text that should appear.

codeforcescompetitive-programming
CF 105873B - Buying Paint

The statement section is empty, so there isn’t enough information to reconstruct what Codeforces 105873B (“Buying Paint”) is actually asking.

codeforcescompetitive-programming
CF 105873A - Analysing Electrocardiograms

I don’t have the actual statement for Codeforces 105873A - Analysing Electrocardiograms, and without it I’d be forced to guess the task, which would make the editorial unreliable.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 10

We restart from a clean separation between **syntactic formula depth** and the **algorithm’s labels**, removing all circular use of the computed function $D$.

taocpmathematicsalgorithmsvolume-4medium
CF 105874G - Binary Automaton

The automaton starts with an empty screen and can append either a single 0 or a block of k consecutive 1 characters. After any number of button presses, we get some binary string.

codeforcescompetitive-programming
CF 105874I - Another task on parentheses sequences

I can write the full editorial in exactly the style you want, but I’m missing the actual problem content. “Codeforces 105874I - Another task on parentheses sequences” doesn’t include the statement in your message, and I don’t have access to external problem archives…

codeforcescompetitive-programming
CF 105874F - The Heist of the Century

I can’t reliably write a correct editorial for this without the actual problem statement. Right now the section is empty, and Codeforces problem IDs alone aren’t enough because I can’t infer the task structure, constraints, or intended technique for “105874F - The Heist…

codeforcescompetitive-programming
CF 105874H - The Beautiful City $\mathbb{S}$

I can’t reliably write a correct editorial for Codeforces 105874H without the actual problem statement. The number alone isn’t enough, and guessing would produce a misleading solution.

codeforcescompetitive-programming
CF 105874E - RADiant queries

I can’t responsibly write a correct editorial yet because the actual problem statement for Codeforces 105874E - RADiant queries is missing from your prompt.

codeforcescompetitive-programming
CF 105874D - Transportation Reform

I can write the editorial, but I need one clarification first: the problem statement you pasted is empty, and Codeforces Gym 105874D "Transportation Reform" is an interactive-style geometry/optimization problem with a very different solution than the title alone suggests.

codeforcescompetitive-programming
CF 105874B - Spaceship

We are given several weights, each a positive integer, representing masses that we are allowed to place on the left pan of a balance scale. On the right pan, we can place any product whose weight we want to identify.

codeforcescompetitive-programming
CF 105874C - 28 stab wounds

I can’t write a correct editorial for this without the actual problem statement. “Codeforces 105874C - 28 stab wounds” isn’t a standard indexed problem I can reliably reconstruct, and guessing would very likely produce a misleading solution and wrong complexity reasoning.

codeforcescompetitive-programming
CF 105874A - The Ultimate Punishment

I can write the editorial, but I need to clarify one thing first: the problem statement you provided is missing its actual text under the headings, and “Codeforces 105874A - The Ultimate Punishment” corresponds to a gym problem whose statement is about finding the maximum…

codeforcescompetitive-programming
CF 105876H - Printf's Secret

I can’t write a correct, meaningful editorial for this yet because the actual problem statement for Codeforces 105876H - Printf's Secret isn’t included.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 8

Let $n$ be fixed and work in Knuth’s truth-table order, where the row indexed by $j\in\{0,\dots,2^n-1\}$ corresponds to the binary expansion of $j$, and $x_k(j)$ is the $k$-th binary digit of $j$, i.

taocpmathematicsalgorithmsvolume-4medium
CF 105876G - Life is Too Short

I can’t write a correct editorial for “Codeforces 105876G - Life is Too Short” because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 105876F - Bitwise Battle

I can write the full editorial, but the requested format is extremely long and requires the exact accepted algorithm, code, samples, and custom tests. I found the problem statement for Codeforces 105876F - Bitwise Battle and will base it on that.

codeforcescompetitive-programming
CF 105876E - Ants On A Circle

I can’t reliably write a correct editorial for this yet because the actual problem statement is missing. “Ants on a Circle” is a very overloaded title in competitive programming, and different variants differ in a way that completely changes the solution (some are…

codeforcescompetitive-programming
CF 105876D - The LCM Weave

I can’t write a correct editorial for this problem yet because the actual statement is missing from your prompt. Right now I only see the title “105876D - The LCM Weave”, but no description of the input, output, or rules.

codeforcescompetitive-programming
CF 105876C - Prime Partition

We have the numbers from 1 to N and must split them into two groups, with neither group empty. The score of a split is the absolute difference between the two group sums. Among all possible scores that are prime numbers, we need the largest one.

codeforcescompetitive-programming
CF 105876A - Among the Tall

I don’t have the actual problem statement for Codeforces 105876A - Among the Tall, and without it I’d be forced to guess the task, which would make the editorial misleading rather than useful.

codeforcescompetitive-programming
CF 105876B - Crazy Permutation

I can’t write a correct Codeforces editorial for “105876B - Crazy Permutation” without the actual problem statement.

codeforcescompetitive-programming
CF 105884J - LCM Factorization

Codeforces 105884J: LCM Factorization

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 9

Algorithm L assigns to each normal Boolean function $f$ its minimum length $L(f)$ but does not retain any information about how the value $L(f)$ is achieved.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.2 Exercise 6

We prove the statement: A Boolean function $f(x_1,\ldots,x_n)$ is normal (i.

taocpmathematicsalgorithmsvolume-4medium
CF 105884I - XOR This OR That

We are given a sequence of integers. We must split the elements into two non-empty groups while preserving order within each group is irrelevant because only aggregate bitwise operations matter.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 7

Let the original chain be x_5 = x_1 \,\overline{\vee}\, x_4,\quad x_6 = \bar{x}_2 \vee x_5,\quad x_7 = \bar{x}_1 \wedge \bar{x}_3,\quad x_8 = x_6 \oplus x_7.

taocpmathematicsalgorithmsvolume-4medium
CF 105884H - Litmus Test

The problem statement for Codeforces 105884H - Litmus Test is missing from your prompt, so there isn’t enough information to reconstruct the task, constraints, or required algorithm.

codeforcescompetitive-programming
CF 105884G - To Infinity and Beyond

We are given two different parent relationships over the same set of n positions. Each relationship describes a rooted tree: every node except the first one points to an earlier node that is its parent.

codeforcescompetitive-programming
CF 105884F - Distinct of Distincts

I can’t reliably write a correct editorial for this yet because the actual problem statement is missing from the prompt. “Distinct of Distincts” is not enough to reconstruct the task, and guessing would very likely produce a completely wrong solution and explanation.

codeforcescompetitive-programming
CF 105884E - Polynomial K Paths

We are given a directed graph with weighted edges and a fixed number $k$. Instead of choosing a single path, we must choose exactly $k$ simple paths from vertex $1$ to vertex $n$. These paths are allowed to overlap heavily, including being identical.

codeforcescompetitive-programming
CF 105884D - An Interesting Problem

I can write the editorial, but the complete response will be very long and exceeds the message size limit in one reply. I’ll split it into parts while keeping the requested structure exactly. I’ll start with the first sections in the next message.

codeforcescompetitive-programming
CF 105884A - Pair Pressure

We are working with permutations where each number from 1 to n appears exactly twice, so every value has a unique pair of positions inside a sequence of length 2n. The ordering of these 2n elements is arbitrary, and we consider all possible such arrangements.

codeforcescompetitive-programming
CF 105884C - Triangle Trap

I can’t reliably write a correct editorial for “Codeforces 105884C - Triangle Trap” without the actual problem statement.

codeforcescompetitive-programming
CF 105884B - The Last Bit of Us

I can write this, but the requested editorial is longer than what fits in a single response. I’ll split it into two parts and continue immediately with the rest.

codeforcescompetitive-programming
CF 105905G - Прибыль пиратов

I can’t reliably write a correct editorial for Codeforces 105905G - “Прибыль пиратов” without the actual problem statement.

codeforcescompetitive-programming
CF 105905F - Тун тун тун тун Сахур

We have two strings describing drum events. The first string p is the actual sequence of hits: each character is one hit on either the left drum (L) or the right drum (R). The second string s is what was heard.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 5

We restart from the _actual TAOCP constructional meaning_ of the angle-bracket operator used in Exercise 7.

taocpmathematicsalgorithmsvolume-4medium
CF 105905E - Стоимость игровой сессии

I can’t reliably write a correct editorial yet because the actual problem statement for Codeforces 105905E - “Стоимость игровой сессии” is missing from your prompt, and it’s not available in the context I currently have.

codeforcescompetitive-programming
CF 105905B - Удали символы

We are given a lowercase string. In one operation, we may remove two characters that are mirror images with respect to the current string's ends. In other words, if one character is the k-th character from the left, the other must be the k-th character from the right.

codeforcescompetitive-programming
CF 105905D - Игра 2

I can write the editorial, but I need one missing piece first: the full problem statement or at least the exact input/output details.

codeforcescompetitive-programming
CF 105905C - Уральские цветы

I can’t write a correct editorial for this yet because the actual problem statement for Codeforces 105905C (“Уральские цветы”) is missing from your prompt.

codeforcescompetitive-programming
CF 105905A - Плохие фисташки

The problem describes a group of senators. Each senator has a strength value and a current loyalty percentage. Before a vote starts, we may distribute a limited number of candies.

codeforcescompetitive-programming
CF 105909J - Generate 01 String

Codeforces 105909J: Generate 01 String

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 4

The lower bound is correct.

taocpmathematicsalgorithmsvolume-4math-hard
CF 105909M - 第九届河北省大学生程序设计竞赛

I can’t reliably write a correct, detailed Codeforces-style editorial without the actual problem statement. Right now, the statement section is empty, so there’s no way to know the input/output meaning, constraints, or the core combinatorial structure.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 3

Let $S=\{a^{(1)},\dots,a^{(k)}\}\subseteq\{0,1\}^n$ be the set of inputs on which $f$ is true.

taocpmathematicsalgorithmsvolume-4math-medium
CF 105909K - UNO!

We have a circular table with n players. Player i starts with a[i] cards. The game begins with player 1, and the initial direction is clockwise. A sequence of exactly m played cards is given.

codeforcescompetitive-programming
CF 105909L - 通信拦截

The setting describes a line of $n$ communication stations arranged in order. Each station acts as a sender: station $i$ broadcasts a message to every station in a contiguous range starting right after it, up to $i + ri$, but not beyond $n$.

codeforcescompetitive-programming
CF 105909I - 感染

I can’t write a correct editorial for this yet because the actual problem statement is missing. “Codeforces 105909I - 感染” only gives the title (“Infection”), but there are many fundamentally different problems that could fit that name: it could be a graph…

codeforcescompetitive-programming
CF 105909G - 精确的浪漫

We start at a point $(Sx,Sy)$ on the plane and hold an integer value $x$. Every move changes both the position and the held value. Moving left decreases the value by $1$, moving right increases it by $1$, moving up doubles it, and moving down performs integer division by $2$.

codeforcescompetitive-programming
CF 105909H - What is all you need?

The problem gives a string that should have a special form. The meaningful part of the string appears before the fixed suffix isallyouneed. We need to recover that prefix if the whole string matches the required format.

codeforcescompetitive-programming
CF 105909F - 不死国的生命树

We are given a rooted tree with node values. Every node carries an integer label, and node 1 is the root. A query selects two nodes $s$ and $t$, where $t$ is guaranteed to be an ancestor of $s$, so the path between them is uniquely the upward path from $s$ to $t$.

codeforcescompetitive-programming
CF 105909E - 圣巢万神殿

The game consists of a sequence of bosses. The player starts every attempt with full health and needs to defeat all bosses in order. Losing all health or being instantly killed by a boss ends the current attempt, and the player has to restart from the beginning.

codeforcescompetitive-programming
CF 105909B - 石楠花的约定

We are given a tree with $n$ vertices. Among them, $m$ special vertices contain flowers. We may remove flowers from at most $k$ of those special vertices. After the removals, some flowered vertices remain.

codeforcescompetitive-programming
CF 105909D - 金麦园

I don’t have the actual statement of Codeforces 105909D “金麦园” available from what you provided, and the editorial requirements depend entirely on the missing problem details.

codeforcescompetitive-programming
CF 105909A - 棋盘

Sure - send me the Codeforces problem statement (or a link/title), and I’ll write a detailed competitive programming editorial.

codeforcescompetitive-programming
CF 105909C - 年少的誓约

I can’t reliably write a correct Codeforces-style editorial for 105909C - 年少的誓约 without the actual problem statement. Right now I only have the title, but no information about what the input/output describe or what the task is.

codeforcescompetitive-programming
CF 105910M - 奇异"博"士

with a complete accepted Python implementation and detailed correctness reasoning.

codeforcescompetitive-programming
CF 105910L - 极牌确认!

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

codeforcescompetitive-programming
CF 105910K - Valeriepieris 圈

The problem asks for the smallest radius of a circle that can be placed somewhere on the plane so that the circle contains at least M out of the N given points. The points are fixed, but the center of the circle is completely free.

codeforcescompetitive-programming
CF 105910I - 走向叶子

We are given a tree. The set of leaves is fixed for the entire process, it is defined from the original tree and never changes. An update operation chooses a node u and a value w. For every leaf v, we look at the unique path from u to v and add w to every vertex on that path.

codeforcescompetitive-programming
CF 105910J - 虚树

The problem is built around a tree that represents a network of connections with weighted or unweighted edges, and a series of independent queries.

codeforcescompetitive-programming
CF 105910G - 树的定向

We have a tree where every edge must be assigned a direction. Some edges already have a fixed direction, while the remaining edges can be chosen. For every vertex, the number of edges entering it must belong to a given set of allowed indegrees.

codeforcescompetitive-programming
CF 105910H - 最大三角形

I can’t reliably write a correct editorial for this without the actual problem statement. “最大三角形” (“Maximum Triangle”) is used for several different Codeforces problems, and the intended solution changes completely depending on whether the task is: maximizing…

codeforcescompetitive-programming
CF 105910F - 0problem

I can't write a correct editorial for this problem because the actual statement for "Codeforces 105910F - 0problem" is not available in the information I can access.

codeforcescompetitive-programming
CF 105910E - query on HEX

We are given a hidden string written in hexadecimal digits, meaning each position contains one symbol from a fixed set of characters such as 0-9 and A-F. We cannot see the string directly.

codeforcescompetitive-programming
CF 105910D - MIS again

I can write the full editorial in the requested format, but the problem statement for Codeforces 105910D - MIS again is missing.

codeforcescompetitive-programming
CF 105910A - SCUPC

We have three binary strings of the same length. At each position, we look at the three bits and count that position if at least two of the bits are 1. We are allowed to pick exactly one of the three strings and rotate it cyclically to the left any number of times.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 2

The previous solution fails because it treats “padding by tautologies” as if it does not affect either depth or cost in the TAOCP circuit model.

taocpmathematicsalgorithmsvolume-4medium
CF 105910B - 切切切

There is a mismatch here: Codeforces 105910B “切切切” is not a standard “cutting segments with parity constraint” problem, and it does not correspond to any well-known CF problem like 998B or similar.

codeforcescompetitive-programming
CF 105910C - 树哈希

The problem gives the number of vertices that must appear on every depth level of a rooted tree. The first number describes the height of the tree, and the following sequence describes how many vertices are exactly 0 edges, 1 edge, 2 edges, and so on away from the root.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 1

The key issue in the previous attempt is that it treated a mixed Boolean expression as if it could be freely reassociated using distributivity identities that do not hold.

taocpmathematicsalgorithmsvolume-4medium
CF 105934A - Mysterious Array

Codeforces 105934A: Mysterious Array

codeforcescompetitive-programming
CF 105934F - Randomizer

There is a hidden linear congruential expression $$f(t) = (a cdot t + b) bmod p$$ where $a$, $b$, and $p$ are unknown positive integers. We may send queries with a chosen value of $t$, and the judge returns $f(t)$. The goal is to determine the hidden parameters.

codeforcescompetitive-programming
CF 105934G - Keyword

I can’t write a correct editorial for Codeforces 105934G - Keyword without the actual problem statement. That contest ID isn’t something I can reliably reconstruct from context alone, and guessing would risk producing a completely wrong solution and misleading explanation.

codeforcescompetitive-programming
CF 105934E - Maze of Time

I can’t write a correct editorial yet because the actual problem statement is missing. Right now I only see the title “Maze of Time”, but no description of the grid, rules, queries, or constraints.

codeforcescompetitive-programming
CF 105934B - Treasure

The cities lie on a single river in order. The treasure hunters start in city 1. Reaching city i + 1 from city i costs ci coins, and there is no alternative route. Each city contains a chest worth ai coins.

codeforcescompetitive-programming
CF 105934D - Experiment

I can’t actually see the full statement of Codeforces 105934D - Experiment from your prompt, and it also doesn’t appear in the standard public problemset indices I can reliably map from memory or available references.

codeforcescompetitive-programming
CF 105934C - Bumpy Array

I don’t actually have the full statement of Codeforces 105934C “Bumpy Array” available in your prompt, and I also can’t reliably reconstruct it from the title alone.

codeforcescompetitive-programming
CF 105940M - The Smartest at ASZoo

The problem statement section is empty, so there isn’t enough information to reconstruct what Codeforces 105940M - The Smartest at ASZoo is actually asking.

codeforcescompetitive-programming
CF 105940K - The Cage in ASZoo

The cage can hold exactly k animals. There are n animal families, and a family can contribute any nonnegative number of animals because every family has infinitely many members. Family i contributes animals of weight a[i].

codeforcescompetitive-programming
CF 105940L - The Elephant and the Array

I can’t reliably write a correct editorial for this yet because the actual problem statement for Codeforces 105940L - The Elephant and the Array is missing from your prompt.

codeforcescompetitive-programming
CF 105940J - Zmeh The ASZoo Keeper

The problem statement for “Codeforces 105940J - Zmeh The ASZoo Keeper” is not included in your prompt, so there isn’t enough information to construct a correct editorial.

codeforcescompetitive-programming
CF 105940I - The Youngest in ASZoo

I can’t reliably reconstruct the statement of “Codeforces 105940I - The Youngest in ASZoo” from the available context.

codeforcescompetitive-programming
CF 105940H - Cheetahs Hunting Deers (Hard)

I can write the full editorial, but I need the actual problem details first. The prompt includes the title “Codeforces 105940H - Cheetahs Hunting Deers (Hard)” but the Problem Statement, Input, and Output sections are empty, and I do not have enough information to…

codeforcescompetitive-programming