brain

tamnd's digital brain — notes, problems, research

41230 notes

TAOCP 7.2.1.2 Exercise 20

We construct an explicit Hamiltonian path on the Cayley graph of the hyperoctahedral group $B_n$, whose vertices are signed permutations of $\{1,\dots,n\}$.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.2.1.2 Exercise 19

Let $\alpha$ be a string of length $n=s+t$ on the alphabet ${+,-,0}$ satisfying the conditions of Exercise 29, so that $\alpha$ contains exactly $s$ signs and $t$ zeros.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.2.1.2 Exercise 18

Let a string $\alpha$ consist of symbols in ${+, -, 0}$.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.2.1.2 Exercise 17

Introduce an additional array $a'_{1}\ldots a'_{n}$ alongside Algorithm P, where at all times $a'_{k}=j$ if and only if $a_{j}=k$.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.2.1.2 Exercise 16

Connection interrupted.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.2.1.2 Exercise 15

Let Algorithm P be executed on a sequence $a_1a_2\cdots a_n$ of distinct elements, with auxiliary arrays $c_1\cdots c_n$ and $o_1\cdots o_n$, and variables $j$ and $s$ as defined in steps P1–P7.

taocpmathematicsalgorithmsvolume-4math-medium
CF 103585F - Giant Sequoia

The problem statement is missing from your prompt, so there is no way to reconstruct the intended task reliably. Codeforces gym problems like 103585F are not uniquely identifiable without the full statement, and any attempt to infer the problem would risk fabricating…

codeforcescompetitive-programming
CF 103586C - Установка модулей GAIA

The brute-force approach would simulate applying the two permutations repeatedly starting from the identity configuration. Each state is a full permutation of size $n$, and from each state we can move to at most two new states.

codeforcescompetitive-programming
TAOCP 7.2.1.2 Exercise 14

The statement claims an invariant relation in Algorithm P: at the beginning of step P5, $a_{j-c_j+s} = x_j$ for all $j$, where $x_1x_2\cdots x_n$ is the initial permutation and $c_1\cdots c_n$, $s$ ar...

taocpmathematicsalgorithmsvolume-4math-medium
CF 103590D - Анонимность наше все

We are given a line of people, each person either potentially infected or healthy, but we never observe their individual state directly. Instead, we receive statements about segments of the line.

codeforcescompetitive-programming
CF 103590B - Великая последовательность

We are given a sequence of positive integers and a fixed multiplier $x$. The goal is to extend the sequence by adding the smallest possible number of new positive integers so that the final multiset of values can be perfectly partitioned into pairs.

codeforcescompetitive-programming
CF 103600L - Grass Field

We are given a set of vertical line segments on a plane. Each segment represents a blade of grass standing on the ground line $y = 0$, extending upward at some fixed $x$-coordinate, with a given height.

codeforcescompetitive-programming
CF 103600J - Химическая точность

We are given several available solutions, each characterized by a salt concentration. We are allowed to take some integer number of grams from each solution, with an upper limit of 10⁴ grams per solution.

codeforcescompetitive-programming
CF 103600H - Таблица

At its core, this task describes an interactive system where you are allowed to make up to 300 queries, after which you must output a single integer $N$ that was supposedly “chosen” in advance.

codeforcescompetitive-programming
CF 103604B - Dungeon

We are given a multi-level dungeon. Each level is a grid of cells, and all levels are connected sequentially through special exit cells. The player starts at the top-left cell of the first level with initial power equal to 1. Each cell in the dungeon behaves like a terrain type.

codeforcescompetitive-programming
CF 103608D - Необычная ловушка

I cannot produce a correct editorial yet because the problem statement is not actually available in the prompt or in a reliable extracted form.

codeforcescompetitive-programming
CF 103608A - In Pursuit of the Penguin

I don’t have the problem statement for “Codeforces 103608A - In Pursuit of the Penguin” available in context, and I can’t reliably reconstruct it from the title alone without risking inventing details.

codeforcescompetitive-programming
CF 103608B - The Great Flood

I can’t write a correct Codeforces editorial for 103608B - The Great Flood because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 103608C - Спасительная загадка

I can’t write a correct editorial yet because the actual problem content is missing. In your prompt, the sections for the statement, input, and output are empty, so there is no information about what the task is asking, what structure the input has, or what needs to be…

codeforcescompetitive-programming
CF 103623B - Unusual Sorting

Let $omega = e^{2pi i/3}$, so $omega^3 = 1$ and $1 + omega + omega^2 = 0$. Write each nonnegative integer $k$ in base $3$ as $$k = sum{j ge 0} kj 3^j, quad kj in {0,1,2}.

codeforcescompetitive-programming
CF 103623E - Гигантский дракон

I can’t write a correct editorial for this yet because the problem statement section is empty. “Codeforces 103623E - Гигантский дракон” isn’t enough to reconstruct the task reliably, and guessing would risk inventing a completely different problem.

codeforcescompetitive-programming
CF 103623D - Force Meter Test

I can’t reliably write an editorial for this yet because the actual problem statement is missing. Right now I only see the title “Force Meter Test”, but no description of what the force meter does, what the inputs represent, or what needs to be computed.

codeforcescompetitive-programming
CF 103623C - Deck for Magic Tricks

I don’t have the actual problem statement for Codeforces 103623C - Deck for Magic Tricks in your prompt, so I can’t reliably reconstruct the solution or write a correct editorial.

codeforcescompetitive-programming
CF 103623A - Eren and the Basement

I can’t reliably reconstruct the full original statement of Codeforces 103623A - Eren and the Basement from available sources, and the problem text is not accessible in a clean, complete form in the context we have.

codeforcescompetitive-programming
CF 103624G - Current Objective: Survive

I can’t reliably write a correct editorial for Codeforces 103624G - Current Objective: Survive because the problem statement (input/output definition, constraints, and rules) is missing from your prompt.

codeforcescompetitive-programming
CF 103624A - Queen Anne's Revenge

Let $omega = e^{2pi i/3}$, so $omega^3 = 1$ and $1 + omega + omega^2 = 0$. Write each nonnegative integer $k$ in base $3$ as $$k = sum{j ge 0} kj 3^j, quad kj in {0,1,2}.

codeforcescompetitive-programming
CF 103624E - Dead Man's Chest

I don’t have the actual statement for Codeforces 103624E - Dead Man’s Chest, and I can’t reliably reconstruct it from the title alone without risking inventing details.

codeforcescompetitive-programming
CF 103624F - Sinking Ship

The problem statement section is empty, so there isn’t enough information to derive the solution or write a correct editorial.

codeforcescompetitive-programming
CF 103624D - Gold Coins Game

The problem statement for Codeforces 103624D - Gold Coins Game is missing from your message, so I can’t correctly reconstruct the solution or write a valid editorial yet.

codeforcescompetitive-programming
CF 103624B - Balanced Cannons

I can’t produce a correct editorial yet because the actual problem statement for Codeforces 103624B - Balanced Cannons is missing from your prompt.

codeforcescompetitive-programming
CF 103624C - One Piece

I don’t have the actual problem statement for Codeforces 103624C - One Piece in your prompt, so I can’t reliably reconstruct the task or produce a correct editorial without guessing.

codeforcescompetitive-programming
CF 103625E - Dead Man's Chest

Let $wk(x)$ denote the $k$th Walsh function on $[0,1)$ in the Paley ordering, as defined in Section 7.2.1.1, so that each $wk$ is a ${pm 1}$-valued step function whose discontinuities occur only at dyadic rationals and whose sign pattern is determined by the binary digits of $k$.

codeforcescompetitive-programming
CF 103625J - Pirate Races

The problem statement for “Codeforces 103625J - Pirate Races” is missing from your prompt, so I don’t have enough information to write a correct editorial or derive any solution.

codeforcescompetitive-programming
CF 103625I - Redbeard's Trials

I can write the full editorial in the exact style you want, but I don’t actually have the statement of Codeforces 103625I - Redbeard’s Trials in the prompt, and I can’t reliably reconstruct it from the title alone without risking inventing the wrong problem.

codeforcescompetitive-programming
CF 103625G - Current Objective: Survive

We are given a game-like process on a structure that behaves like a sequence of states, where each state represents a position in a world and transitions between states represent possible moves.

codeforcescompetitive-programming
CF 103625H - X Marks the Spot

I’m missing the actual problem statement for Codeforces 103625H - X Marks the Spot, so I can’t safely reconstruct the solution or write a correct editorial yet.

codeforcescompetitive-programming
CF 103625F - Sinking Ship

I can’t write a correct, detailed Codeforces editorial without the actual problem statement. “Codeforces 103625F - Sinking Ship” is not included in your message, and I don’t have reliable access to that specific problem content.

codeforcescompetitive-programming
CF 103625C - One Piece

I can’t reliably write a correct editorial for “Codeforces 103625C - One Piece” because the actual problem statement is missing from your prompt. Without the statement, any solution would be guesswork, and that would defeat the purpose of a serious editorial.

codeforcescompetitive-programming
CF 103625D - Gold Coins Game

The problem statement is missing from your prompt, so I can’t reliably reconstruct the rules, game mechanics, or required output for “Codeforces 103625D - Gold Coins Game”.

codeforcescompetitive-programming
CF 103627L - Curly Racetrack

We are given a rectangular grid that represents a partial configuration of a racetrack made of curved tiles. Some cells are already fixed as containing a curly tile, while others are empty and can later be filled by the admin.

codeforcescompetitive-programming
CF 103627J - Diameter Pair Sum

We are working with a tree that is being dynamically modified, and each query asks us to compute a quantity that depends on distances inside a connected component of that tree.

codeforcescompetitive-programming
TAOCP 7.2.1.2 Exercise 13

Let Algorithm R denote the revolving-door generation of $t$-combinations of ${0,1,\dots,n-1}$ in the order described in Section 7.

taocpmathematicsalgorithmsvolume-4math-medium
CF 103627I - Streetlights

We are given a line of streetlights, each with a height, and a sequence of updates and queries. The updates change the height of a specific streetlight over time, while the queries ask us to count how many “visible pairs” of streetlights currently exist.

codeforcescompetitive-programming
CF 103627H - Endless Road

We are given a collection of segments on a line, where each segment represents a member and the interval of road they cover. The road itself is conceptually continuous, but the only interesting structure comes from segment endpoints.

codeforcescompetitive-programming
CF 103627E - Yet Another Interval Graph Problem

We are given a collection of weighted intervals on a line. Each interval can be thought of as an edge that connects its endpoints, and if two intervals overlap or touch through a chain of overlaps, they belong to the same connected component in the induced interval graph.

codeforcescompetitive-programming
CF 103627D - Two Bullets

We are given a sequence of values indexed from left to right. Each index represents a building, and each building has a height.

codeforcescompetitive-programming
CF 103627C - AND PLUS OR

We are given a universe of elements indexed from 0 to N − 1. Every subset of this universe is associated with a value through a function a(S).

codeforcescompetitive-programming
CF 103627B - Bingo

We are working with an $n times n$ grid where each cell can either be filled or left empty. The goal is to construct a pattern of empty cells that avoids forming any complete “bingo line”, where a bingo line corresponds to a fully empty row, fully empty column, or a fully…

codeforcescompetitive-programming
CF 103630J - Рудольф и разноцветная таблица

The problem statement is missing from the prompt, so I can’t reconstruct the logic, constraints, or required output for “Codeforces 103630J - Рудольф и разноцветная таблица” reliably.

codeforcescompetitive-programming
CF 103630I - Рудольф и подарочные наборы

I’m missing the actual problem statement for Codeforces 103630I - “Рудольф и подарочные наборы”, so I can’t reliably reconstruct the logic or write a correct editorial yet.

codeforcescompetitive-programming
CF 103630H - Рудольф и вышивка крестиком

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only have the title (“Rudolf and cross-stitch embroidery”), but no description of the rules, input format, or what needs to be computed.

codeforcescompetitive-programming
CF 103630B - Рудольф и игра

Let $X[0],X[1],dots,X[n-1]$ be the array to be permuted, and let the inner loop in (42) denote the operation that is executed once per produced permutation, typically a visit or output of the current array state.

codeforcescompetitive-programming
CF 103630F - Рудольф и пчёлы

The problem statement for Codeforces 103630F - “Рудольф и пчёлы” is missing from your prompt, so there isn’t enough information to construct a correct editorial. Right now I don’t know: - what the input represents (grid, tree, queries, etc.

codeforcescompetitive-programming
CF 103630G - Рудольф и Бернард

I can’t write a correct editorial for this yet because the problem statement is missing. “Codeforces 103630G - Рудольф и Бернард” alone doesn’t include the actual task description, so there’s no way to reliably reconstruct what is being asked, the…

codeforcescompetitive-programming
CF 103630D - Рудольф и мастерское зачарование

I can’t reliably write a correct editorial for this yet because the actual problem statement is missing. Right now I only have the title (“Rudolf and master enchantment”), but no description of what the input represents, what operations are allowed, or what needs to be…

codeforcescompetitive-programming
CF 103630E - Рудольф и звезды

The statement for CF 103630E - “Рудольф и звезды” is missing from your prompt, so I don’t have enough information to reconstruct the problem or produce a correct editorial.

codeforcescompetitive-programming
CF 103630A - Рудольф и сборка компьютеров

I don’t have the actual statement for Codeforces 103630A (“Рудольф и сборка компьютеров”) in your prompt, so I can’t reliably reconstruct the problem or write a correct editorial without guessing.

codeforcescompetitive-programming
CF 103630C - Рудольф и IQ ПФО

I’m missing the actual problem statement for Codeforces 103630C - “Рудольф и IQ ПФО” in your prompt.

codeforcescompetitive-programming
TAOCP 7.2.1.2 Exercise 12

Let Algorithm R generate successive $t$-combinations $c_t \dots c_2 c_1$ in revolving-door order, and let $j_k$ denote the index computed in step R3 on the $k$th visit, so that step R3 identifies the...

taocpmathematicsalgorithmsvolume-4math-medium
CF 103631A - Урок физкультуры

Let $X[0],X[1],dots,X[n-1]$ be the array to be permuted, and let the inner loop in (42) denote the operation that is executed once per produced permutation, typically a visit or output of the current array state.

codeforcescompetitive-programming
CF 103631D - Прожекторы

We are given a set of points, each point representing a projector placed on a plane. Every projector must be assigned one of several fixed directions. Once a direction is chosen, the projector illuminates a region of the plane determined by its position and its direction.

codeforcescompetitive-programming
CF 103631B - Оптимизация закупок

We are given two arrays that define weighted intervals on the same index line. One array contributes “cost” values and the other contributes “profit” values.

codeforcescompetitive-programming
CF 103631C - Интересные выходные

We are effectively dealing with a process that builds a rooted tree dynamically from a sequence of instructions, and then answers queries about relationships between nodes in that tree.

codeforcescompetitive-programming
CF 1036328 - Большие вызовы

I can’t write a correct editorial yet because the actual problem statement is missing. Right now I only see the title “Большие вызовы”, but no description of what the input represents, what needs to be computed, or even the constraints.

codeforcescompetitive-programming
CF 1036327 - Тяжелый груз

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only see the title (“Тяжелый груз”) but no description of the input, output, constraints, or what needs to be computed.

codeforcescompetitive-programming
CF 1036325 - Максимизация выигрыша

Let $X[0],X[1],dots,X[n-1]$ be the array to be permuted, and let the inner loop in (42) denote the operation that is executed once per produced permutation, typically a visit or output of the current array state.

codeforcescompetitive-programming
CF 1036326 - Экспедиция на Сириус

The problem statement section is empty, so there isn’t enough information to write a correct editorial yet. For a Codeforces editorial, I need at least: the full statement (or a link / text), plus input/output format and constraints.

codeforcescompetitive-programming
CF 103633B - Floor or xor ?

We are given an array of integers and three parameters: a target value and a modulus. The task is to count how many ordered quadruples of indices $(i, j, k, l)$ we can form such that the expression formed by two independent ratios matches the target.

codeforcescompetitive-programming
CF 103633A - Hatchet

We are given a sequence that represents a structured process, where the input describes an ordered list of values. The task is to choose two cut positions inside this sequence so that the array is split into three consecutive non-empty segments.

codeforcescompetitive-programming
CF 103634B - Xor or floor ?

We are given a collection of test cases, each test case contains two integers. For each pair, we are asked to compute two different values derived from these numbers: one is obtained by applying bitwise XOR, and the other is obtained by integer division in the floor sense.

codeforcescompetitive-programming
CF 103634A - Bamboo Coloring

I don’t have the actual statement of Codeforces 103634A (“Bamboo Coloring”) in your prompt, so I can’t reliably reconstruct the problem or write a correct editorial without risking inventing details.

codeforcescompetitive-programming
CF 103634C - Jump

I don’t have the statement for Codeforces 103634C - Jump in context, and I can’t reliably reconstruct the problem from the ID alone (it looks like a Gym or private archive problem).

codeforcescompetitive-programming
TAOCP 7.2.1.2 Exercise 113

Let Algorithm R generate successive $t$-combinations $c_t \dots c_2 c_1$ in revolving-door order, and let $j_k$ denote the index computed in step R3 on the $k$th visit, so that step R3 identifies the...

taocpmathematicsalgorithmsvolume-4hm-project
CF 103637L - Long integer

We are maintaining a very large integer that starts as an initial decimal string. The number is then modified step by step by a sequence of operations. Each operation either appends a single digit to the right end of the current number or removes the rightmost digit.

codeforcescompetitive-programming
CF 103637K - K-ones xor

We are given an array of $n$ integers, each represented with at most $m$ bits. We are allowed to choose a mask $x$, also an $m$-bit number, but with the restriction that it contains at most $k$ set bits.

codeforcescompetitive-programming
CF 103637J - Jenga

We are asked to count how many valid Jenga towers can be formed using exactly $n$ identical blocks, under a specific notion of stability. A tower is built in horizontal layers. Each layer contains one or more blocks, and adjacent layers are oriented perpendicular to each other.

codeforcescompetitive-programming
CF 103637I - Items in boxes

We are given two integers. One of them, $n$, determines how many boxes exist, specifically $2n$ boxes in total. The second value, $a$, describes how many distinct items are inside each box, and every box is independent of the others. From each box we must pick exactly one item.

codeforcescompetitive-programming
CF 103637G - Geometric shapes

We are given a rectangular grid of size $n times m$. One cell $(r, c)$ is forbidden and must remain empty. All other cells must be covered completely using tetrominoes, where each tetromino occupies exactly four cells and can be any of the standard Tetris shapes under rotation…

codeforcescompetitive-programming
CF 103637F - Function analysis

We are given a permutation-like sequence $p = (1, 2, dots, n)$. From this sequence we repeatedly sample $m$ elements, where each position is chosen independently and uniformly from the $n$ positions, so repetitions are allowed and the resulting multiset is not necessarily…

codeforcescompetitive-programming
CF 103637D - Dull game

We are given a sequence of heap sizes, and we are allowed to repeatedly modify individual heap values. After each modification, we must select a subsequence of indices that satisfies a very specific game-theoretic condition.

codeforcescompetitive-programming
CF 103637E - Elegance in moves

We are working on a very large chessboard where most cells are usable, but some disjoint rectangular regions are forbidden. The rectangles do not overlap, and each cell belongs to at most one of them.

codeforcescompetitive-programming
CF 103637B - BSUIR Open X

We are given a collection of strings, each representing the code name of a task set. From this collection we must choose exactly two distinct strings, and we are allowed to place them in either order, concatenating one after the other.

codeforcescompetitive-programming
CF 103637C - Crossed out letter

We are given two strings, both of the same length. Each of them is known to come from some unknown original string by deleting exactly one character, but not necessarily the same position in both cases.

codeforcescompetitive-programming
CF 103640J - Joining Pairs

Let $x in [0,1)$ and write its dyadic expansion $$x = 0.x1 x2 x3 ldots,qquad xj in {0,1}.$$ Let $rj(x)$ denote the $j$-th Rademacher function, $$rj(x) = (-1)^{xj}.

codeforcescompetitive-programming
CF 103640M - Most Ordered Way

The problem statement for “Codeforces 103640M - Most Ordered Way” is not included in your message, so I can’t accurately reconstruct the solution or write a meaningful editorial yet.

codeforcescompetitive-programming
CF 103640K - KIARA is a Recursive Acronym

I don’t have the actual statement for Codeforces 103640K (“KIARA is a Recursive Acronym”), so I can’t safely reconstruct the intended model, constraints, or solution path without risking inventing details that may be wrong.

codeforcescompetitive-programming
CF 103640L - Leaving Yharnam

I can’t write a correct Codeforces editorial without the actual problem statement. “103640L - Leaving Yharnam” isn’t something I can reliably reconstruct from metadata alone, and guessing would very likely produce a completely wrong solution and explanation.

codeforcescompetitive-programming
CF 103640I - Invested Money

The problem statement is missing, so I don’t have the actual rules, inputs, or required computation for “Codeforces 103640I - Invested Money”. Without that, I’d be guessing the entire solution, which would defeat the purpose of a correct editorial.

codeforcescompetitive-programming
CF 103640H - Hamilton - The Musical

I can’t write a correct, detailed editorial for “Codeforces 103640H - Hamilton - The Musical” without the actual problem statement. Right now the prompt contains only the title and format placeholders, but no description of the input/output or the task.

codeforcescompetitive-programming
CF 103640B - Because, Art!

Let $x in [0,1)$ and write its dyadic expansion $$x = 0.x1 x2 x3 ldots,qquad xj in {0,1}.$$ Let $rj(x)$ denote the $j$-th Rademacher function, $$rj(x) = (-1)^{xj}.

codeforcescompetitive-programming
CF 103640F - Fields Division

The problem statement is not included in your message, so I don’t have enough information to reconstruct what “Fields Division (103640F)” is asking or what the input/output represent.

codeforcescompetitive-programming
CF 103640G - Generator Tree

I don’t have the actual statement of Codeforces 103640G - Generator Tree in your prompt, so I can’t safely reconstruct the problem or produce a correct editorial without risking inventing details.

codeforcescompetitive-programming
CF 103640D - Daily Turnovers

We are given a sequence of daily financial results, where each element represents the company’s profit or loss on that day. A negative value means loss, positive means profit.

codeforcescompetitive-programming
CF 103640E - Expedition Plans

The prompt is missing the actual content of Codeforces 103640E - Expedition Plans (problem statement, input/output description, constraints, and samples).

codeforcescompetitive-programming
CF 103640A - Ancient Towers

The editorial request can’t be completed yet because the actual problem statement is missing. Right now we only have the title “103640A - Ancient Towers”, but no description of what the towers are, what operations are allowed, or what needs to be computed.

codeforcescompetitive-programming
CF 103640C - Cyclists versus Clouds

I can’t reliably reconstruct Codeforces 103640C (“Cyclists versus Clouds”) from the title alone, and I don’t have the actual statement in your prompt.

codeforcescompetitive-programming
CF 103643T - Revert to Zero

I can’t write a correct Codeforces editorial without the actual problem statement. “Codeforces 103643T - Revert to Zero” is not enough to reconstruct the task reliably, and guessing would lead to a completely wrong solution and analysis.

codeforcescompetitive-programming
CF 103643S - Gin-chan's Odd Jobs

I cannot reliably reconstruct a correct editorial for Codeforces 103643S - Gin-chan’s Odd Jobs from the available context, because the actual problem statement is not present in the accessible sources, and this specific Gym problem is not part of the standard indexed…

codeforcescompetitive-programming
CF 103643K - Cards

Let $x in [0,1)$ and write its dyadic expansion $$x = 0.x1 x2 x3 ldots,qquad xj in {0,1}.$$ Let $rj(x)$ denote the $j$-th Rademacher function, $$rj(x) = (-1)^{xj}.

codeforcescompetitive-programming
CF 103643R - Quantum Fluctuations

I can’t write a correct editorial for this yet because the actual problem statement for Codeforces 103643R - Quantum Fluctuations is missing from your prompt.

codeforcescompetitive-programming