brain
tamnd's digital brain — notes, problems, research
43815 notes
We are given a tower of monsters arranged in a line from bottom to top. Each floor has a monster with a fixed strength. A player starts with some initial strength $x$.
We are given a string and we want to count ordered pairs of substrings where the first substring is lexicographically greater than the second one, with the additional restriction that the first substring must start strictly earlier in the string.
We are given two arrays of equal length, and we want to cut the index range from 1 to n into several consecutive segments. Each index must belong to exactly one segment, and the segments must cover the whole array without gaps or overlap.
We are given two integers, $n$ and $k$, and a sequence of $n$ fractions whose structure follows a fixed pattern. The denominators are all the same value, while the numerators form a simple arithmetic progression starting from 1 up to $n$.
We are given a collection of axis-aligned rectangles on a 2D plane. Each rectangle has a weight, and we want to pick exactly two rectangles such that they do not overlap in the sense that there is no point that lies inside both rectangles, and maximize the sum of their weights.
Let $G$ be the Cayley graph of $Sn$ with generating set $${sigma,tau}, qquad sigma = (1,2,dots,n), quad tau = (1,2),$$ where $n ge 3$ is odd.
We are given a grid containing $n$ mirrors placed at distinct coordinates. Each mirror has a type, either A or B, which determines how a light ray changes direction when it hits that mirror.
We are given a tree, and we consider every simple path inside it. A simple path is any sequence of vertices where each vertex is visited at most once, so in a tree this is exactly the unique path between any two chosen endpoints, including the degenerate case where both…
We rebuild the analysis from the actual control structure of Algorithm P (plain changes, Johnson–Trotter) rather than any external digit model.
The task describes an output-only situation where there is no input to read. We are only required to print a single string that would be considered valid as an answer.
We are given a damage skill whose output depends on how long it is charged. The damage grows linearly, but the growth rate changes once the charging time crosses a threshold $k$. Before or at $k$ seconds, each second contributes $x$ damage.
Let $G$ be the Cayley graph of $Sn$ with generating set $${sigma,tau}, qquad sigma = (1,2,dots,n), quad tau = (1,2),$$ where $n ge 3$ is odd.
We are given a train route described as a sequence of stations in order along the line. Some subset of these stations are stopping points, while the rest are passed without stopping.
We are asked to construct a sequence of $n$ distinct positive integers such that any three chosen numbers from the sequence can form the side lengths of a non-degenerate triangle.
We are given a current clock reading in 24-hour format and two limits, one allowing the clock to be shifted backward by at most a minutes and another allowing it to be shifted forward by at most b minutes.
We are given a set of people who can potentially share information, represented as an undirected graph. Each person is a node, and an edge between two nodes means they are acquaintances. The detective calls people in a fixed order, from 1 to n.
Let $G$ be the Cayley graph of $Sn$ with generating set $${sigma,tau}, qquad sigma = (1,2,dots,n), quad tau = (1,2),$$ where $n ge 3$ is odd.
Two players, John and Paul, alternately say a word, starting with John. Each time a player speaks, they choose an integer strength within their personal range. John can choose any value from 1 up to $RJ$, and Paul from 1 up to $RP$.
We are given a strictly increasing list of coin denominations, where each denomination divides the next one. This means the system behaves like a chained multiplicative structure rather than arbitrary coin values.
We are given several independent triples of integers. For each triple, we need to decide whether it is possible to construct two non-negative integers $x$ and $y$ such that three conditions hold simultaneously: their bitwise AND equals a given value $a$, their bitwise OR…
We are given a rectangular board with sides a and b, placed in a fixed orientation so that its bottom edge is horizontal. Over k days, identical square stickers were placed one per day, each sticker also oriented so its bottom edge is horizontal.
We address the errors directly and rebuild the argument in a fully rigorous way.
We are given a set of hats, each described by four numbers. These numbers define a structured bargaining process between a buyer and a seller.
We are given three stacks of books. Every book has a unique label from 1 to s, where s is the total number of books across all stacks. Each stack is described from bottom to top, so each stack is essentially a sequence where only the last element is currently accessible.
We are given a multiset of digits, all of them nonzero, and we are allowed to arrange them in any order to form a number. The task introduces two participants who both construct numbers from the same digit set.
There are several voting districts, and each district contains a number of polling stations. Every station has a predicted amount of fraudulent ballots that would be added there if nothing is done. The goal is to reduce the total fraud by placing observers.
We are given a row of digits. In one move, we may pick a single position and increase or decrease that digit by one, staying within the range 0 to 9. The goal is not to reach a fixed target string, but to reach any configuration where some digit value appears at least k times.
We are given a collection of identical gold bars, and each bar can be oriented in one of three effective ways, contributing a height of either a, b, or c. All bars must be used exactly once, and we stack them into a single tower.
We are given a line of $n$ stones, each colored either black or white. The goal is to determine whether, by repeatedly applying allowed local recoloring operations, it is possible to transform the entire line so that all stones end up with the same color.
Two contestants are tracking how many programming problems they solve over time. Each of them already has some number of solved problems, and then they continue solving at a constant daily rate.
We are given a rectangular grid of cities with height h and width w. Each cell is a city, and from any city the news can be passed in one day to other cities reachable by a chess knight move, meaning the usual eight L shaped moves, as long as the destination cell stays inside…
The flaw in the previous solution is the attempt to decompose the dynamics into independent subgames.
Represent the binomial tree $T_n$ in the left-child, right-sibling representation of exercise 2.
A weak order on ${1,\dots,n}$ is represented in Exercise 105(b) by a sequence $a_1a_2\dots a_n$ where $a_j$ equals the number of symbols $\prec$ that precede $j$ in the underlying relation.
The task describes a transformation on a structured arrangement of elements, which you can think of as a grid or a set of positions laid out in a fixed geometry.
The reviewer’s objection to part (b) rests on a mistaken separation between “ordered partitions” and the block indexing used in the encoding.
We are given a sequence of tower heights placed along a line, where each position has a unique height value. The task is to count how many triples of indices $i < j < k$ form a strictly increasing sequence in both position and height, meaning $hi < hj < hk$.
We are given a collection of magical artifacts, each with a positive value $wi$. The hero starts with zero magical power. Each artifact must be used exactly once, and each one can be activated in one of two ways.
We are given a small grid, where each cell is a character representing a tiny square tile of a drawing. Each tile is either empty or contains a diagonal segment.
We are given a small grid, at most 20 by 20, where each cell contains a direction character among N, S, E, and W.
We are working in a positional numeral system with base $k$, where numbers are written using digits from $0$ to $k-1$. A number is called “sufficiently round” if, when written in base $k$, its representation ends with at least $n$ zero digits.
Let S(a_1\ldots a_n)=\sum_{k=1}^n k a_k.
Let $S_n$ act on ${1,\dots,n}$ in Knuth’s standard one-line notation.
We reframe the problem in a way that makes the adjacency condition precise and then build a recursive cyclic Gray ordering that preserves it under the embeddings required by involutions.
Represent the binomial tree $T_n$ in the left-child, right-sibling representation of exercise 2.
Represent the binomial tree $T_n$ in the left-child, right-sibling representation of exercise 2.
Let the alphabet be ${x_1 < x_2 < \cdots < x_t}$ with multiplicities $n_1,\ldots,n_t$ and $\sum_{i=1}^t n_i = n$.
The failure in the previous solution is entirely caused by an inconsistent global state variable $t$.
We are given a binary schedule of length $n$, where each position represents what Arseniy plans to do in a specific hour: either training or eating. The schedule is fixed as a string over two characters, where one letter stands for training and the other for eating.
We are given a Fibonacci-like sequence where the first two terms are fixed as $F1 = 1$ and $F2 = 2$, and every later term is the sum of the previous two. This produces a deterministic infinite sequence of integers.
The problem statement is missing from your prompt (the sections for Problem, Input, and Output are empty). Without the actual description, any editorial would be guesswork, and that would defeat the purpose of a correct Codeforces-style writeup.
I can’t reliably write an editorial without the actual problem statement for Codeforces 103671B - it isn’t included in your prompt, and I don’t have access to it from here.
I don’t have the actual problem statement for “Codeforces 103671A - Village Bridge” in your prompt, so I can’t produce a correct editorial yet without risking inventing details.
The reviewer’s diagnosis is correct: the previous proof failed because it tried to identify _submultisets_ with _Algorithm L states_, which are not unique.
The problem statement is missing from your prompt, so there isn’t enough information to reconstruct what needs to be solved.
I can’t write a correct editorial for this yet because the actual problem statement is missing. “Codeforces 103677M - Grape Juice Country” isn’t enough on its own to reconstruct the task reliably, and anything I write without the statement would risk inventing…
The problem statement is missing from your prompt, so I don’t have enough information to write a correct Codeforces-style editorial.
I don’t have the actual statement of “Codeforces 103677K - Wine Grapes” in the prompt, so I can’t reliably reconstruct the problem or produce a correct editorial.
I don’t have the actual statement for Codeforces 103677J “Trail Mix Ad” in the prompt you provided, so I can’t reliably reconstruct the problem, constraints, or solution without risking inventing details.
I can’t write a correct editorial for Codeforces 103677I - Faction Feud because the actual problem statement (and thus the rules, constraints, and required transformations) is missing from your prompt.
The problem statement section is empty, so there isn’t enough information to reconstruct what “Alexander the Grape” is asking for.
We are given a set of grape types, each type having a required minimum usage amount. The winery produces bottles of wine, and each bottle is formed by selecting exactly $n-1$ distinct grape types out of the $n$ available, using one unit of each selected type.
I can’t write a correct editorial for “Codeforces 103677F - Sour Grapes” because the problem statement is missing from your prompt.
I don’t have the actual statement of Codeforces 103677E “Festa des Vermar” in the prompt, and I can’t reconstruct it reliably from the title alone without risking inventing details.
I don’t have the actual problem statement for Codeforces 103677C - Raisin Box in your prompt, and I can’t reliably reconstruct it from the title alone without risking inventing details.
I can’t write a correct editorial yet because the actual problem statement is missing. Right now I only see the title “Codeforces 103677B - With Grape Power comes Grape Responsibility”, but there is no description of the input, output, or rules.
I can’t write a correct editorial for this yet because the actual problem statement (what “Raiser Mais” is asking) is missing. Right now I only have the title and metadata, but no description of the input/output or the task itself.
I’m missing the actual problem statement for “Codeforces 103678G - Бернард и прятки на дереве”, and without it I can’t reliably reconstruct the correct model, constraints, or solution.
I don’t have the actual problem statement for Codeforces 103678H - “Бернард и глубокая река” in the prompt, and without it I can’t correctly reconstruct the model, constraints, or intended solution path.
I could not reliably recover the exact Codeforces statement for 103678F from available public archives or mirrors, which strongly suggests this problem is either from a very recent or less-indexed round, or the title has been mis-copied.
I cannot reliably reconstruct the exact statement of Codeforces 103678E - Бернард и футболки from available indexed sources.
I’m missing the actual problem statement for Codeforces 103678D - “Бернард и кирпичная стена” (the section is empty in your prompt), so I can’t reliably reconstruct the task or produce a correct editorial.
We are working with a one-dimensional array that is initially empty or filled with zeros, and we are asked to process two kinds of operations. One operation updates a contiguous segment by adding an arithmetic progression across its positions.
Let M=\{n_1\!
I can’t write a correct editorial for this problem as-is because the problem statement section is empty. Without the actual rules of the “train parade” process, any solution, reasoning, or complexity analysis would be guesswork and would almost certainly be wrong.
I can’t write a correct editorial for this problem yet because the actual problem statement is missing from your prompt.
We are given a binary grid made of black and white cells. Black cells form a picture created by stamping several fixed shapes onto the grid. There are two possible stamp types.
We are given a multiset of candy values. JB must choose any subset of these candies. After he chooses a subset, we compute the average value of that chosen subset, call it $X$.
We are given a directed graph where each edge is either active or inactive, and we are allowed to toggle edges between these two states over time. Initially, every edge is active.
We are given a frog that always lives on the unit circle centered at the origin. Its position is described by an angle in degrees, so a value ds corresponds to the point (cos(πds/180), sin(πds/180)).
We are given a fixed string and many independent queries. Each query picks a substring, and two players then play a turn-based game on that substring.
We are not being asked to solve a standard substring or parsing task directly. Instead, we are given a very small rewriting language that behaves like a constrained string rewriting system, and our job is to output a program in that language which, when executed, decides…
We are trying to move a point from a start location $S$ to a target location $T$ on a 2D plane. Movement is continuous and unrestricted in direction. Under normal conditions, the character walks with constant speed $V1$.
We are given a permutation of length $n$. For each position $i$, we look at how many smaller values appear to its left and how many smaller values appear to its right.
We are simulating a progression through a linear sequence of stages, where each stage must be cleared before moving forward. At any stage, a single attempt can either succeed, letting us advance to the next stage, or fail, which keeps us at the same stage but reduces health.
We are given a set of items, each item having a value and two possible prices. Normally every item i costs a fixed amount $ai$, but if we choose a segment $[l, r]$, then every item inside that segment becomes more expensive and costs $bi$ instead.
Algorithm $L$ enumerates permutations (and multiset permutations) by maintaining an inversion table $c_1,\dots,c_n$ satisfying $0 \le c_j < B_j,$ where $B_j$ is the admissible bound for coordinate $j$...
We are given two integers, a starting value and a target value. We are allowed to repeatedly apply one of two operations on the current value. The first operation adds a fixed positive odd number x, and the second operation subtracts a fixed positive even number y.
We are given two groups of participants in a stock market-like system. One group contains people who want to buy shares, and each of them specifies a maximum price they are willing to pay.
We are given a single string composed only of lowercase English letters. The task is to scan this string from left to right and whenever the consecutive characters form the substring "cjb", we must insert a comma immediately after that occurrence.
Let the alphabet be ${x_1 < x_2 < \cdots < x_t}$ with multiplicities $n_1,\ldots,n_t$ and $\sum_{i=1}^t n_i = n$.
We are given a string and a target string of the same length. In one operation, we pick one of two allowed cut positions, split the string into a prefix and suffix, then perform a specific sequence of rearrangement: swap the two parts and reverse the whole result.
We are given a rooted tree with nodes labeled from 1 to n, with node 1 as the root. A token starts on some node, and the process evolves in discrete steps. In each step, we pick a node v uniformly at random from all n nodes.
We are given a tree with a value attached to every node. A “path query” here is not just about summing node values along a path.
We are given a sequence of words indexed from 1 to n, and alongside it a string of the same length consisting of three possible characters: opening parentheses, closing parentheses, and dashes. The parentheses form a correctly matched structure.
We are given a circular arrangement of n pearls. Each pearl i has a non-negative integer value ci. The process is interactive in the sense that we repeatedly choose a starting pearl i, but only if ci is at least 1 and there are enough pearls currently still present.
We are asked to count how many different ordered arrays of positive integers sum up to a given number $k$. Order matters, so $[1,2]$ and $[2,1]$ are considered different, even though they have the same sum.
Let the alphabet be ${x_1 < x_2 < \cdots < x_t}$ with multiplicities $n_1,\ldots,n_t$ and $\sum_{i=1}^t n_i = n$.
There are only seven possible positions on a small board. Two identical pieces start on two different positions among these seven, and the goal is to move them, one move at a time, until they occupy two other distinct target positions.
We are given an array of integers, and for every pair of indices $i < j$, we compute a derived value from the product of the two numbers after stripping away even prime exponents in a very specific way.