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tamnd's digital brain — notes, problems, research

43815 notes

CF 1051932 - Две сестры

Absolutely. Please provide the Codeforces problem (either the full statement, a link, or just the contest ID and problem letter, e.g. "CF 1978C").

codeforcescompetitive-programming
CF 1051931 - Змейка

I don’t have the actual problem statement for Codeforces 1051931 - “Змейка” in your message, and without it I’d be forced to guess the task, which would make the editorial incorrect.

codeforcescompetitive-programming
CF 1051955 - Джерримендеринг

I can’t write a correct editorial yet because the problem statement is missing. Right now I only have the title “Джерримендеринг”, but no description of what the input represents, what operations are allowed, or what needs to be computed.

codeforcescompetitive-programming
CF 1051954 - Железная дорога

I don’t have the actual problem statement for Codeforces 1051954 - “Железная дорога”, so I can’t reliably reconstruct the solution, constraints, or even the task definition.

codeforcescompetitive-programming
CF 1051952 - Лазерная пушка

The problem describes a spaceship with two independent lasers. Each laser has a power value and a reload time. A laser starts charging immediately, and after each shot it needs its reload time before it can shoot again.

codeforcescompetitive-programming
CF 1051953 - Не был предателем...

I don’t have the actual statement of Codeforces 1051953 “Не был предателем…”, and without it I can’t produce a correct editorial.

codeforcescompetitive-programming
CF 1051951 - Кинотеатр

Sure - I can do that. Please paste the Codeforces problem statement (or at least the problem link / number). If there are multiple parts (input/output, constraints, samples), include them too.

codeforcescompetitive-programming
CF 105198K - Center of Attraction?

We are given a line of n = b + g positions. Exactly g of these positions are assigned to girls, and the remaining b positions are boys. This means every valid configuration is simply a choice of which g indices among 1..n contain girls.

codeforcescompetitive-programming
CF 105198L - Kalopsia Sequence

We are maintaining a binary string of parentheses where each character is either an opening or closing bracket. The string changes over time, and after each update we may need to answer whether a chosen substring forms a valid regular bracket sequence.

codeforcescompetitive-programming
CF 105198M - Too Easy?

The grid is infinite, and each test case describes a starting tile and a destination tile. A move changes exactly one coordinate by one unit.

codeforcescompetitive-programming
CF 105198J - Monke, Potato and Their Knight Game

The board is infinite, so the only information that matters is the relative position between the starting square and the chosen destination square. For every test case, we are given two coordinates for the knight's initial position and two coordinates for the target position.

codeforcescompetitive-programming
CF 105198I - Optimal Tree Exploration

We are given a rooted tree where each node carries a numeric value. Every query gives two starting nodes, one for Alice and one for Bob. From their respective starting points, each person is allowed to move only downward along parent to child edges.

codeforcescompetitive-programming
CF 105198H - Stupid Game

We are given a circular arrangement of n balls. Each ball initially has value 1, and two players alternate removing one ball per turn starting with player X. When a ball is removed, its value is added to the current player’s score.

codeforcescompetitive-programming
CF 105198G - Surprise Gift

We need build an n x n grid of positive integers. The grid is not given, so the task is purely constructive: we can choose any values as long as every row sum, every column sum, and the two diagonal sums are powers of two. The input contains only the size of the grid.

codeforcescompetitive-programming
CF 105198F - Not A Giveaway

Each test gives a target amount of “energy units” measured in lit segments on a 7-segment display. Every decimal digit consumes a fixed number of segments when lit.

codeforcescompetitive-programming
CF 105198E - Jor Shongkot

We are given an array of length $n$, where $n$ is odd, and we are allowed to repeatedly apply a very unusual global operation: choose a positive integer $x$, and XOR every element of the array with $x$ in one shot.

codeforcescompetitive-programming
CF 105198D - Geometry Class

Sure. Please provide the Codeforces problem statement (including constraints, examples, and any notes), and I’ll write a competitive programming editorial with: - Problem restatement - Key observations - Detailed derivation of the algorithm - Proof of correctness -…

codeforcescompetitive-programming
CF 105198A - Monke's Favourite Function

We are given a function defined on integers x interpreted through their binary representation. Each integer corresponds to a set of bit positions, and every number y ≤ x with y & x = y is exactly a submask of x, meaning it only uses bits that are already present in x.

codeforcescompetitive-programming
CF 105198C - Alpha Beta

We are given a string of length $n$ made of lowercase English letters. Instead of treating the string as fixed character positions, we are allowed to “select” some occurrences of each letter and organize these selected indices into 26 groups, one per letter.

codeforcescompetitive-programming
CF 105198B - 21---0?

We are given a sequence of daily solve counts indirectly. The original array contains how many problems were solved on each day, but only the sum of the recent days is provided.

codeforcescompetitive-programming
CF 105200H - Hierarchy Mess

Sure. Please provide the Codeforces problem statement (including constraints, examples, and any notes if available), and I’ll write a detailed competitive programming editorial covering: - Problem intuition - Key observations - Derivation of the algorithm - Proof of…

codeforcescompetitive-programming
CF 105200J - Joust

The task reduces a competition to a single comparison. Each participant has a record of how many problems they solved, and we are also given the moment at which each participant finished their solving session or reached their final recorded state.

codeforcescompetitive-programming
CF 105200E - Earthquake

Sure - I can do that. Please paste the Codeforces problem statement (or at least the link / full description), and tell me if you want: - full editorial (intuition + proof + complexity + code) - or short editorial (just idea + key insight) - or step-by-step solution…

codeforcescompetitive-programming
CF 105200I - Inversion Test

We are given a sequence of numbers and the task revolves around understanding how far it is from being “clean” in terms of order.

codeforcescompetitive-programming
CF 105200F - Foreign Language

The problem deals with converting one string into another using a small set of primitive editing operations. Think of having a source text written in one “foreign language” alphabet and a target text in another.

codeforcescompetitive-programming
CF 105200G - Greatest Math Problem

Sure. Please provide the Codeforces problem statement (or a link, title, and constraints), and I’ll write a competitive programming editorial with: - Problem intuition - Key observations - Derivation of the algorithm - Proof of correctness - Complexity analysis -…

codeforcescompetitive-programming
CF 105200D - Don't Get Caught

We have a rectangular hall represented as a grid. Kauã starts in the top-left cell and wants to reach the bottom-right cell. Some cells contain guards, and each guard watches every cell in one straight direction until another guard blocks the view.

codeforcescompetitive-programming
CF 105200A - Array Issue

We are given an array of integers, and the task is to evaluate a classic “maximum subarray” quantity repeatedly as we extend the array from left to right.

codeforcescompetitive-programming
CF 105200C - Correcting Exams

We are given a very small computational task: a pair of integers represents a fraction, and we need to decide whether that fraction is at least one half. You can think of it as checking whether some obtained value is “not worse than half of the maximum possible”.

codeforcescompetitive-programming
CF 105200B - Breaking Up Words

Sure. Please provide the Codeforces problem statement (including constraints, examples, and any clarifications you have), and I’ll write a detailed competitive programming editorial. I’ll structure it like a typical Codeforces editorial: 1. Problem Restatement 2.

codeforcescompetitive-programming
CF 105201K - kostka Loves Hashing

We are given a string and a target value $k$. For every distinct substring $t$, we look at how many times it appears inside the string and multiply that frequency by the substring’s length. If this product equals $k$, that substring is considered valid.

codeforcescompetitive-programming
CF 105201M - Inversion Test

We are given several independent test cases, each consisting of an array. The task is not to compute the inversion count itself, but to find a shortest contiguous segment of the array that preserves exactly the same number of inversions as the full array.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 83

The error in the previous solution is exactly the unjustified assumption that the partial cube embedding behaves like a full product space.

taocpmathematicsalgorithmsvolume-4project
CF 105201L - Little Gas Station

The city is a tree: every intersection is connected to every other one through exactly one path. Intersection 1 always contains the original gas station, while other intersections may temporarily contain replicas.

codeforcescompetitive-programming
CF 105201I - Intergalactic Conference

We are given two sets of aliens placed on a number line of galaxies. Each galaxy index is an integer position, and each occupied galaxy stores a count of aliens belonging to exactly one of two species. We choose a single galaxy as a conference location.

codeforcescompetitive-programming
CF 105201H - House Rules

We have a line of n k positions, numbered by distance from the entrance. Each position initially contains one shoe, and every person owns exactly k shoes. The array a tells us the owner of the shoe currently placed at each position. A day consists of two random events.

codeforcescompetitive-programming
CF 105201J - Juiceless Class

Codeforces 105201J: Juiceless Class

codeforcescompetitive-programming
CF 105201G - Gifting Problems

Working

codeforcescompetitive-programming
CF 105201B - Big Numbers

Sure - please paste the full Codeforces problem statement (or at least the link / contest + problem letter). Once I have it, I’ll write a proper competitive programming editorial with: - problem intuition - key observations - full solution idea - correctness explanation -…

codeforcescompetitive-programming
CF 105201E - Exotic Algorithm (Easy Version)

We have a string where every position is treated as a vertex in a graph. Two positions become connected by an edge when the substring between those positions, including both endpoints, reads the same from left to right and right to left.

codeforcescompetitive-programming
CF 105201F - Further Exotic Algorithm (Hard Version)

We are given a string and we turn it into a graph whose vertices are the positions of the string. Between any two positions $i$ and $j$, we draw an edge if the substring from $i$ to $j$ reads the same f

codeforcescompetitive-programming
CF 105201D - Deaga Loves Sequences

We start with an empty array of length $n$. Two kinds of operations are performed. One operation injects a structured numeric sequence into a contiguous segment $[l, r]$, adding its values element by element onto the array.

codeforcescompetitive-programming
CF 105201A - Attacking Bees

I can write the full editorial in the requested format, but the complete version with every required section, traces, test harness, and a full Python implementation is longer than the maximum response size available here.

codeforcescompetitive-programming
CF 105201C - Colorful Date

Working

codeforcescompetitive-programming
CF 105204L - Бинпоиск решает всё!

We have a permutation of the numbers from 1 to n. A value x must be found by a binary search procedure that is run on this unsorted permutation. The procedure does not look for the position of x directly.

codeforcescompetitive-programming
CF 105204M - Повар и каша

We are simulating a queue of students where the order is not fixed. Each student has two attributes: a greed value ki, which determines how they are placed when they return, and a cooking time factor si, which determines how long they spend eating once they receive food.

codeforcescompetitive-programming
CF 105204K - Игра <<Десяточка>>

I can’t write a correct Codeforces editorial from just the problem code “105204K - Игра «Десяточка»” with an empty statement section.

codeforcescompetitive-programming
CF 105204I - Дороги, которые мы выбираем

We are given a line of houses indexed from 1 to n. Each house owner has a preference for which side of a road they want to live on: either the left side or the right side.

codeforcescompetitive-programming
CF 105204J - Правильный суп

Absolutely. Please provide the Codeforces problem (either the problem statement, the problem link, or just the contest ID and problem letter, e.g. 1985C or 2031D). I'll write a comprehensive competitive programming editorial that typically includes: 1.

codeforcescompetitive-programming
CF 105204H - Хэштег

We are given a post consisting of words and a set of “mandatory” words that must all appear in a final hashtag. The hashtag is constructed from the chosen words of the post, each word contributing its full length to the total cost.

codeforcescompetitive-programming
CF 105204G - Кирилл и грибы

This request is for a very large document that exceeds the maximum length I can produce in a single response. A complete editorial following all of your required sections, including detailed explanations, a full proof sketch, complete Python solution, worked examples…

codeforcescompetitive-programming
CF 105204D - Борис и ракушки

We are given a line of students. Each student is described by two parameters. One of them tells how many times they still need to be served food, and the other tells how long it takes them to finish eating one serving once they receive it. The cook operates in rounds.

codeforcescompetitive-programming
CF 105204E - Снежок

Codeforces 105204E: Снежок

codeforcescompetitive-programming
CF 105204F - Предсказания Серафима

Absolutely. Please provide the Codeforces problem (either the problem statement, the problem link, or the problem code such as CF 2050C). I'll write a comprehensive editorial in the style commonly seen after Codeforces contests, including: 1.

codeforcescompetitive-programming
CF 105204C - Ботинки или сандалии

The route is described by a string consisting of '0', '1', and '?'. A segment marked '0' must be walked in sandals, a segment marked '1' must be walked in boots, and a segment marked '?' may be assigned either type of footwear.

codeforcescompetitive-programming
CF 105204A - Разбиваем лагерь

We are given three types of participants who must be placed into identical tents, each tent having capacity for up to three people. The twist is that each type imposes a constraint on how they are allowed to share a tent. Introverts insist on being alone in their tent.

codeforcescompetitive-programming
CF 105204B - Фейерверки

Two independent fireworks systems produce bursts at perfectly regular intervals. The first system needs exactly a minutes to prepare each launch, so its fireworks appear at times a, 2a, 3a, .... The second system works the same way with period b, producing bursts at b, 2b, 3b, ..

codeforcescompetitive-programming
CF 105206F - ROAD TO BE LEGEND

We are given several independent test cases. In each test case there are $N$ girls, and each girl $i$ is assigned a segment $[li, ri]$.

codeforcescompetitive-programming
CF 105206B - Путешествие

We are given a long sequence of non-negative integers. We are also given a target value x. The task is to look inside the sequence and find a contiguous segment whose elements sum exactly to x. Among all such segments, we are asked to pick one with the maximum possible length.

codeforcescompetitive-programming
CF 105206E - Рома торговец

Absolutely. Please provide the Codeforces problem (either the problem statement, a link, or the problem ID), and I'll write a competitive-programming-style editorial. A typical editorial will include: 1. Problem Restatement - concise summary of the task. 2.

codeforcescompetitive-programming
CF 105206A - Захар и скины

Захар имеет n различных скинов и хочет выбрать ровно k из них. Порядок выбора не имеет значения, важен только состав выбранного набора.

codeforcescompetitive-programming
CF 105206D - 12 725 9

Absolutely. Please provide the Codeforces problem (either the problem statement, problem link, or problem ID). I'll write an editorial in the style commonly seen after Codeforces contests, including: 1. Problem Restatement - concise summary. 2.

codeforcescompetitive-programming
CF 105206C - Лень

This request asks for a complete competitive programming editorial with multiple long sections, correctness proof, implementation explanation, worked examples, edge case analysis, and a full test suite.

codeforcescompetitive-programming
CF 105212A - Самое вкусное путешествие

We are given a tree of castles, rooted conceptually at node 1 because that is where the traveler starts at time 1. Time advances in discrete steps, and at every step the traveler must move along exactly one edge of the tree.

codeforcescompetitive-programming
CF 105212D - Я больше никогда не буду играть в Minecraft

Absolutely. Please provide the Codeforces problem (either the problem statement, the problem link, or the problem ID/contest number).

codeforcescompetitive-programming
CF 105212C - Пиццерия Пеппино

Sorry, but I can't produce or fabricate a complete editorial with algorithm, proof, implementation, worked examples, and tests for a specific competitive programming problem when the original problem statement is incomplete or corrupted.

codeforcescompetitive-programming
CF 105212B - Моя магическая лаба

Absolutely. Please provide the Codeforces problem (either the problem statement, the problem ID like 1985C, or a link), and I'll write a competitive-programming style editorial. A typical editorial will include: 1. Problem Observation - key insights and patterns. 2.

codeforcescompetitive-programming
CF 105213D2 - Невиданный массив

Absolutely. Please provide the Codeforces problem (either the problem statement, the problem link, or the contest/problem ID, such as CF 2000C or Codeforces Round 975 (Div. 2) - Problem D).

codeforcescompetitive-programming
CF 105213C2 - Новый фильм

I can’t reliably write a correct editorial for this problem yet because the statement isn’t included. “Codeforces 105213C2 - Новый фильм” doesn’t give enough information on its own, and guessing would risk inventing the wrong task, constraints, and solution.

codeforcescompetitive-programming
CF 105213A2 - На заре приключений

I can't write a correct editorial for this problem because the prompt does not include the actual problem statement.

codeforcescompetitive-programming
CF 105213B2 - Клинок рассекающий строки

I can absolutely write a complete Codeforces editorial in that format, but I don't have the actual problem statement for Codeforces 105213B2 "Клинок рассекающий строки".

codeforcescompetitive-programming
CF 105254U - Toy Train Tracks

Absolutely. Please provide the Codeforces problem (either the problem statement, problem link, or problem ID), and I'll write a comprehensive competitive programming editorial in the style typically found after contests. The editorial will typically include: 1.

codeforcescompetitive-programming
CF 105254Z - Archaeological Recovery

I can’t write a correct Codeforces-style editorial for this yet because the actual problem statement is missing from your prompt. Right now I only see the title “Archaeological Recovery”, but no description of the task, input format, or output requirements.

codeforcescompetitive-programming
CF 105254Y - Compression

I can absolutely write that editorial, but I need the full problem statement first. Right now, the prompt only includes the title: Codeforces 105254Y - Compression while the Problem Statement, Input, and Output sections are empty.

codeforcescompetitive-programming
CF 105254W - Riddle of the Sphinx

Codeforces 105254W: Riddle of the Sphinx

codeforcescompetitive-programming
CF 105254X - Quartets

I can't write a correct editorial for this problem from the information provided. The prompt contains only the title, while the actual problem statement, input/output specification, constraints, and samples are missing.

codeforcescompetitive-programming
CF 105254V - Three Kinds of Dice

I can't write a correct editorial for this problem from the information in your prompt because the actual problem statement is missing.

codeforcescompetitive-programming
CF 105254T - Carl's Vacation

I can write the full editorial in the exact style you requested, but I’m missing the actual problem content. “Codeforces 105254T - Carl's Vacation” isn’t a standard indexed problem I can reliably reconstruct from the title alone, and guessing would risk producing a…

codeforcescompetitive-programming
CF 105254S - Bridging the Gap

I can absolutely write that editorial, but I don't have the actual problem statement or enough information to reconstruct the algorithm.

codeforcescompetitive-programming
CF 105254R - Zoo Management

I can’t write a correct Codeforces-style editorial for this yet because the actual problem statement is missing. Right now I only see the title “Zoo Management”, but no description of what operations are performed, what the input format is, or what needs to be computed.

codeforcescompetitive-programming
CF 105254Q - Doing the Container Shuffle

I can’t write a correct editorial yet because the actual problem statement for Codeforces 105254Q - Doing the Container Shuffle is missing from your prompt (the section is empty).

codeforcescompetitive-programming
CF 105254P - Turning Red

The editorial can’t be written yet because the actual problem content is missing. Right now the statement, input, and output sections are empty, so there’s nothing to reconstruct the task from.

codeforcescompetitive-programming
CF 105299L - The Tree-Mendous Game of Stones

The problem statement is missing from your prompt, so I don’t have the actual rules of the game, input format, or required output. Without that, I can’t produce a correct editorial, and I’d be forced to guess the problem structure, which would make the solution unreliable.

codeforcescompetitive-programming
CF 105299K - The Great Treasure Dilemma

Codeforces 105299K: The Great Treasure Dilemma

codeforcescompetitive-programming
CF 105299J - Students

The editorial request can’t be completed as written because the actual problem statement for “Codeforces 105299J - Students” is missing from your message.

codeforcescompetitive-programming
CF 105299I - Starry Night

I can’t write a correct Codeforces-style editorial for “105299I - Starry Night” because the actual problem statement is missing from your prompt. Right now there’s no information about what the input represents, what needs to be computed, or even the constraints.

codeforcescompetitive-programming
CF 105299H - Quantum Realms

I can write the full editorial in the exact style you want, but I’m missing the actual problem content. Right now I don’t have the statement for “Codeforces 105299H - Quantum Realms”, so I don’t know what the input represents, what needs to be computed, or what the…

codeforcescompetitive-programming
CF 105299G - Origami

The problem statement section is empty, so there is no information about what “Origami” (Codeforces 105299G) is actually asking. Without the actual rules of the problem, any editorial would be guesswork, and that would defeat the goal of a correct, re-derivable solution.

codeforcescompetitive-programming
CF 105299F - Magic Path

The problem statement for Codeforces 105299F “Magic Path” is missing from your prompt, so I don’t have the actual rules of the movement, grid/graph structure, or what needs to be computed.

codeforcescompetitive-programming
CF 105299D - Golf

We do not actually have the statement for Codeforces 105299D “Golf” available in the prompt, and it is not retrievable from standard CF archives in a way that guarantees correctness from guessing alone.

codeforcescompetitive-programming
CF 105299E - K Segments

The problem statement section is empty, so I don’t have the actual definition of what “K Segments” is asking. For Codeforces editorials, the solution depends entirely on the precise rules about segments, constraints, and what needs to be optimized or counted.

codeforcescompetitive-programming
CF 105299A - Autocomplete

We are given a list of visited webpage addresses and a short prefix string that the user has already typed. The task is to simulate an autocomplete feature: among all stored page addresses that start with this prefix, we must return the one that is smallest in lexicographic…

codeforcescompetitive-programming
CF 105299C - Dark Matter

I can’t write a correct editorial for this yet because the actual problem content is missing. Right now you only provided the title (“Codeforces 105299C - Dark Matter”), but the statement, input/output format, and constraints are required to reconstruct the solution.

codeforcescompetitive-programming
CF 105299B - Bob

I’m going to be direct about a mismatch first: the statement for “Codeforces 105299B - Bob” is not a standard public Codeforces problem in the main archive, and it does not appear in a stable, retrievable form from the usual problemset indices.

codeforcescompetitive-programming
CF 105300L - Spin To Win

I can’t write a correct editorial yet because the problem statement is missing. Right now I only know the title “Spin To Win”, but there are no rules about what the “spin”, the input format, or the required output actually are.

codeforcescompetitive-programming
CF 105300I - Pollen

The system models a garden of flowers where each flower contains an integer amount of pollen. Over time, a sequence of bees arrives, and each bee always chooses one flower that currently has the maximum pollen.

codeforcescompetitive-programming
CF 105300J - Shepherd

The problem statement for “Codeforces 105300J - Shepherd” is missing from your message, so there isn’t enough information to reconstruct the task, constraints, or required output.

codeforcescompetitive-programming
CF 105300K - Sorting Network

I don’t have the actual problem statement for Codeforces 105300K - Sorting Network, and without it I can’t reliably derive the algorithm, constraints, or even the expected I/O format.

codeforcescompetitive-programming
CF 105300H - Payday Quest

I can’t write a correct editorial for this yet because the actual problem statement for Codeforces 105300H - Payday Quest is missing from your prompt.

codeforcescompetitive-programming
CF 105300G - Pants

I can’t write a correct editorial yet because the problem statement is missing. “Codeforces 105300G - Pants” is not enough to reconstruct the task reliably, and guessing would risk inventing an entirely different problem.

codeforcescompetitive-programming