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tamnd's digital brain — notes, problems, research

41641 notes

CF 106063J - Juan vs Frank

The problem reduces the whole story to a single economic decision repeated for as many friends as possible. Each friend requires buying one identical item that costs a fixed amount of money, and Juan has a limited budget.

codeforcescompetitive-programming
CF 106063K - Kilometric Intersection

The problem asks us to measure how much two road segments on a number line overlap. Each segment is a closed interval, so it includes both endpoints, but the answer is based on length, meaning a single touching point contributes zero.

codeforcescompetitive-programming
CF 106063L - Los Ratones III

I’m missing the actual problem statement for Codeforces 106063L - Los Ratones III, and without it I can’t reliably reconstruct the intended solution or write a correct editorial.

codeforcescompetitive-programming
CF 106063H - Heritage of Acatlán

We are given two strings. The first one is a long “spell” string $S$, and the second is a shorter pattern string $T$. The core quantity of interest is the number of ways to pick indices from $S$ so that the characters at those indices, read in order, form exactly $T$.

codeforcescompetitive-programming
CF 106063G - Gatuno's Descent into Psychopathy

The problem models a value that decreases by the same multiplicative factor after every operation. Gatuno starts with a heart size H1. After each bite, the current heart size is multiplied by (B - 1) / B, so every operation makes the value smaller.

codeforcescompetitive-programming
CF 106063I - Isaac and MOD Convolution

I’m missing the actual problem statement for Codeforces 106063I - Isaac and MOD Convolution, and without it I can’t safely reconstruct the intended solution.

codeforcescompetitive-programming
CF 106063F - Fantastic Robot

We are given a grid of size $N times M$, where each cell is either free or blocked. A robot starts at a specific free cell and wants to reach a target free cell.

codeforcescompetitive-programming
CF 106063E - El Juego del Calamar

We are given a tower shaped as a sequence of floors. Each floor contains a small number of rooms, and between consecutive floors there are directed stairs that connect some rooms on floor t to rooms on floor t+1.

codeforcescompetitive-programming
CF 106063D - Doubled Sequence II

The task asks us to build a sequence of length 2n containing every number from 1 to n exactly twice. For a number i, the two copies must be separated by exactly i positions, which means if their indices are l and r, then r - l = i + 1. This is a classic Langford pairing variant.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 35

Let $B_1,\dots,B_p \in \{0,1\}^n$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 106063C - Colorful Polygon

Got it. Please paste the Codeforces problem statement (or link + problem name), and I’ll write a full competitive programming editorial for it. If you want, also tell me the level of detail you expect (short / standard / very detailed with proofs and implementation notes).

codeforcescompetitive-programming
CF 106063A - Archmage's Crystals

Sure - please paste the full Codeforces problem statement (or link + key details). Once you send it, I’ll write a proper competitive programming editorial with: - intuition - step-by-step derivation - optimal algorithm - complexity analysis - edge cases - reference…

codeforcescompetitive-programming
CF 106063B - Bytelandia's stones

I can write the full editorial, but the response will exceed the message length limit if I include every requested section, the full solution, traces, and tests in one message. I’ll provide it in two parts: 1. Problem Understanding through Algorithm Walkthrough. 2.

codeforcescompetitive-programming
CF 106069G - Gamer's Karma Farming Strat

We are given a single day represented as a timeline from second 0 to second 86399. Along this timeline there are several disjoint intervals, each representing a scheduled task. When a task starts, we must immediately decide whether to perform it or ignore it.

codeforcescompetitive-programming
CF 106069H - Halting Zero Permutation

We are given a positive integer $N$, and we must arrange the numbers $1$ through $2N$ into a permutation. We then break this permutation into consecutive pairs.

codeforcescompetitive-programming
CF 106069L - Land of the Golden Butterflies

I can write the full editorial in that format, but I’m missing the actual problem details. The statement section in your prompt is empty, and I couldn’t reliably identify the problem from only “Codeforces 106069L - Land of the Golden Butterflies”.

codeforcescompetitive-programming
CF 106069D - Do You Want to Build a Christmas Tree?

I cannot fit a complete editorial of the requested length and all required sections into a single response without exceeding the message limit.

codeforcescompetitive-programming
CF 106069F - Flying Pig Borrowing Log

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

codeforcescompetitive-programming
CF 106069E - Extradimensional Cosmic Phenomenon

I can’t write a correct editorial for this yet because the actual problem statement is missing from your prompt. Right now I only have the title “Extradimensional Cosmic Phenomenon”, but no description of the input, output, or rules.

codeforcescompetitive-programming
CF 106077G - Uranus

We are given a collection of probes, each characterized by two limits: how much temperature it can tolerate and how much wind it can withstand. Each probe also has a construction cost.

codeforcescompetitive-programming
CF 106077F - Saturn

We are given a target string t that represents the claim Shani wants to prove. She has a sequence of recorded data strings. She may choose any subset of these strings, but the chosen strings must keep their original order when concatenated.

codeforcescompetitive-programming
CF 106077E - Jupiter

The task describes a 2D grid representing space on Jupiter, where each cell belongs to one of several horizontal “bands”. Each cell can be empty, blocked by a storm, be the starting position, or be the destination. The key twist is that the grid is not static.

codeforcescompetitive-programming
CF 106077D - Mars

Got it. Please send the full Codeforces problem statement (or at least the link / contest + problem letter), and I’ll write a proper competitive programming editorial with: - clear intuition - step-by-step derivation - edge cases - complexity analysis - reference…

codeforcescompetitive-programming
CF 106077B - Mercury

We have a ciphertext string made of lowercase letters. Every character in the string has been shifted by the same Caesar cipher offset, but the offset is unknown. We are also given several target phrases.

codeforcescompetitive-programming
CF 106077A - Sun

I can’t reliably write a correct editorial for Codeforces 106077A - Sun without the actual problem statement. This particular ID corresponds to a Gym-style problem, and there isn’t enough information in your prompt (input/output definitions, constraints, or even the task…

codeforcescompetitive-programming
CF 106077C - Earth

Sure-please send the Codeforces problem statement (or at least the link / problem name). If you want, also tell me: - whether you want a full editorial (intuition + proof + code) or just solution idea - preferred language for code (C++ / Python) Once I have the problem, I’ll…

codeforcescompetitive-programming
CF 106078J - Pluto

I can write the editorial, but I’m missing the actual problem content. The title “Codeforces 106078J - Pluto” does not map to a publicly available Codeforces problem statement I can reliably identify, and the statement sections in your prompt are empty.

codeforcescompetitive-programming
CF 106078I - Neptune

We are given several recipes, each describing how a crafting device with a fixed number of slots behaves when it is filled with ingredients. A recipe is a pattern over k positions, where each position is either empty or contains a specific ingredient type.

codeforcescompetitive-programming
CF 106078H - Uranus

Each probe can be described by two limits and a cost. One limit is how much temperature it can survive, the other is how much wind it can survive. A probe is usable at a location only if it handles both conditions at the same time.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 34

Let $N=2^n$ and let $F\subseteq\{0,1\}^n$ be chosen uniformly among all $m$-subsets.

taocpmathematicsalgorithmsvolume-4hm-project
CF 106078G - Saturn

We have a target string t and a list of recorded data strings. We may choose any subset of the recorded strings, but their original order cannot change. The chosen strings are concatenated, and the goal is to make the target string appear as a substring as many times as possible.

codeforcescompetitive-programming
CF 106078F - Jupiter

The problem models a system where you are given a collection of time intervals, and each interval represents an event that can either contribute to or consume some resource, depending on its type.

codeforcescompetitive-programming
CF 106078D - Earth

We are given a sequence of stone masses arranged in a line. From this line, we are allowed to choose a single contiguous segment. Once a segment is chosen, we evaluate its “enjoyment” based on the distribution of values inside it.

codeforcescompetitive-programming
CF 106078E - Mars

We are managing a small collection of milk jugs that travel between Mars and Earth. A spaceship trip either goes from Mars to Earth or from Earth to Mars. When a jug reaches Earth on a Mars-to-Earth trip, it is immediately filled.

codeforcescompetitive-programming
CF 106078C - Game on Venus

We are given an array of length 3n. The game proceeds by repeatedly selecting groups of three elements that will be removed together, and each such group is formed in a constrained way.

codeforcescompetitive-programming
CF 106094E - Max Mex Bamboza

Codeforces 106094E: Max Mex Bamboza

codeforcescompetitive-programming
CF 106094M - Ahlan Ahlan bel3eed

We are given a fixed string of lowercase letters. The string changes over time through point updates, but the structure of the problem does not depend on how the string was built, only on its current state when each query is asked.

codeforcescompetitive-programming
CF 106094N - A-to-B-Kedavra

I can’t reliably reconstruct Codeforces 106094N - A-to-B-Kedavra from the title alone, and writing a correct editorial without the actual statement would risk inventing constraints and logic that don’t match the problem.

codeforcescompetitive-programming
CF 106094K - 3awdat al3lakat

I can’t reliably write a correct Codeforces editorial for “106094K - 3awdat al3lakat” because the problem statement (input/output definition and constraints) is missing.

codeforcescompetitive-programming
CF 106094L - Darabona bel Interactive!!!

Sure-please send the Codeforces problem statement (or at least the link / full text). Once I have it, I’ll write a proper competitive programming editorial with: - Problem summary - Key observations / intuition - Step-by-step solution - Proof of correctness - Complexity…

codeforcescompetitive-programming
CF 106094J - Let the tree fall

We are given a straight line of trees placed at increasing positions along a street. Every tree has the same height $h$.

codeforcescompetitive-programming
CF 106094I - Ammar is back electricity is not

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

codeforcescompetitive-programming
CF 106094G - How did we get here?

The problem describes an infinite grid of integer coordinates where cells are classified by the value of the Chebyshev radius, meaning a cell belongs to layer $k$ if $max( Movement is normally allowed in the four cardinal directions, but stepping into a wall cell is forbidden.

codeforcescompetitive-programming
CF 106094H - You delete matrices I delete memories

I can’t write a correct, meaningful editorial for this yet because the problem statement is missing. “Codeforces 106094H - You delete matrices I delete memories” is referenced, but there are no details about: what the input matrix represents, what operations are allowed…

codeforcescompetitive-programming
CF 106094F - Hate-matrix Potter

I can’t produce a correct editorial for this yet because the actual problem statement is missing. “Codeforces 106094F - Hate-matrix Potter” isn’t something I can reliably reconstruct from the title alone, and guessing would almost certainly lead to inventing…

codeforcescompetitive-programming
CF 106094D - The Red Herring Fallacy

I don’t have the actual problem statement for Codeforces 106094D - The Red Herring Fallacy in your prompt, and without it I’d be forced to guess the task, which would make the editorial unreliable.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 27

Let m=|\mathcal F|,\qquad n=|\mathcal G|,\qquad N=m+n.

taocpmathematicsalgorithmsvolume-4math-hard
CF 106094C - Yum Yum Numbers

We are given a multiset of numbers, each representing a “flavor score” of a candy. The task is to repeatedly combine these numbers into larger values using a fixed rule: we pick two available numbers, merge them into a single new number equal to their sum, and repeat until…

codeforcescompetitive-programming
CF 106094A - Matrix Bel Lotus

The problem gives a 5 by 5 grid containing exactly one cell with the value 1 and all other cells containing 0. A move consists of swapping two neighboring rows or swapping two neighboring columns.

codeforcescompetitive-programming
CF 106094B - Elkataeb Eltabseemeah

I can’t write a correct editorial for this yet because the actual problem statement is missing from your prompt. Right now I only have the title “106094B - Elkataeb Eltabseemeah”, but no description of the task, input format, constraints, or samples.

codeforcescompetitive-programming
CF 106096H - Rocket Cycle

We are interacting with a system that hides two distinct integers on a line from 1 to n, call them x₁ and x₂ with x₁ < x₂. We do not know their locations, and the only way to extract information is by issuing queries at chosen positions. Each query is a position x.

codeforcescompetitive-programming
CF 106096G - Pancakes

We are given a one-on-one fight between two units that exchange damage every second. Each unit has a fixed attack value and a fixed health value, and every second both deal damage simultaneously: your unit reduces the opponent’s health by its attack, and the opponent reduces…

codeforcescompetitive-programming
CF 106096E - To Leap or Not to Leap

The problem asks for the fastest way to move exactly n units. The character can either walk any distance at a fixed speed a, or perform a leap of exactly b units. A leap always takes 3 seconds.

codeforcescompetitive-programming
CF 106096F - Bandit and Bridges (Easy)

Sure - I can do that, but I’ll need the full problem statement first. Please paste the Codeforces problem (or give me the contest + problem letter), and tell me if you want the editorial to include things like: - intuition / idea discovery - full proof - implementation details…

codeforcescompetitive-programming
CF 106096D - Did His Time Come?

I can write the full editorial in exactly that style, but I’m missing the only thing needed to do it correctly: the actual problem statement. “Codeforces 106096D - Did His Time Come?

codeforcescompetitive-programming
CF 106096B - Pancakes (Easy Version)

We are looking at a fight between two units that trade blows every second. Your unit starts with an attack value and a health value, and the opponent has its own attack and health.

codeforcescompetitive-programming
CF 106096C - Mega Knight

We are given a grid with n rows and m columns. Each cell contains a positive value representing the reward obtained if that cell is affected by a spell. We choose exactly one cell as the center of an attack.

codeforcescompetitive-programming
CF 106096A - Deck Building

The problem is about building a Clash Royale deck from paired cards. We have two arrays, where index i describes a pair of cards with costs a[i] and b[i]. When building the deck, we cannot take only one card from a pair.

codeforcescompetitive-programming
CF 106097H - Bandit and Bridges

I don’t have the actual statement for Codeforces 106097H - Bandit and Bridges in your prompt (the problem body is empty), so I can’t reliably reconstruct the intended model, constraints, or solution technique without risking hallucination.

codeforcescompetitive-programming
CF 106097E - Pancakes

Two fighters engage in a deterministic duel that unfolds in discrete seconds. Each second both creatures simultaneously deal damage: your creature reduces the opponent’s health by its attack value, and the opponent reduces your creature’s health by its attack value.

codeforcescompetitive-programming
CF 106097F - Rocket Cycle

We are trying to locate two hidden tower coordinates on a line of positions from 1 to n. The two towers have positions x1 < x2. We cannot see them directly, but we can ask about any position x. The answer tells us which tower a rider would hit.

codeforcescompetitive-programming
CF 106097G - Mortar Mayhem

I cannot safely write a correct full editorial yet because I still need to resolve a mismatch between the information I initially assumed and the actual statement. From the contest page, the real problem is: Each of the $n$ points (mortars) sits on a 2D grid.

codeforcescompetitive-programming
CF 106097B - Did His Time Come?

We are given a non-decreasing sequence of submission times, each representing when Anton solved a problem. Time is measured in hours on an infinite timeline. There is a parameter m that defines how we interpret “days,” but the twist is that a day is not fixed globally.

codeforcescompetitive-programming
CF 106097D - Bandit and Bridges (Easy)

I can write the full editorial, but I need the actual problem statement/details for Codeforces 106097D - Bandit and Bridges (Easy).

codeforcescompetitive-programming
CF 106097C - To Leap or Not to Leap

We are given a single starting point, and we want to reach a target distance using two types of moves. One move advances a fixed small amount per unit time, and another move is a special jump that covers a larger fixed distance but consumes a fixed, nontrivial amount of time.

codeforcescompetitive-programming
CF 106097A - Mega Knight

I can write the editorial, but I need to resolve one mismatch first: Codeforces 106097A “Mega Knight” appears to refer to a grid problem where the task is to maximize the sum of values covered by a plus-shaped attack region.

codeforcescompetitive-programming
CF 106098M - MEDAA, Farouk, and Bald

We are given a positive integer n as a binary string. We need to count how many positive integers x exist such that the binary representation of x has no more bits than n, and the three values n + x, n The key part of the problem is understanding when addition behaves exactly…

codeforcescompetitive-programming
CF 106098K - Farouk and MEX Sum

We are given a permutation of length $n$, meaning it contains each value from $0$ to $n-1$ exactly once. For every contiguous segment of this permutation, we compute its MEX, the smallest non-negative integer that does not appear in that segment.

codeforcescompetitive-programming
CF 106098L - MEDAA and subsequences

The statement section is empty in what you provided, so there’s no way to reconstruct the actual task reliably.

codeforcescompetitive-programming
CF 106098J - Bald and Eslam

We are given a connected undirected graph. A vertex is chosen uniformly at random. Then one of its incident edges is chosen uniformly at random and removed from the graph.

codeforcescompetitive-programming
CF 106098I - MEDAA and Totients

For every number $ai$, Meda computes $$f(ai)=prod{p mid ai}left(1-frac1pright)$$ where the product runs over the distinct prime divisors of $ai$.

codeforcescompetitive-programming
CF 106098H - Farouk and Tape

We are given a tape indexed by all integers, extending infinitely in both directions. The coloring is highly structured: it consists of alternating blocks of black and white, and every block has the same unknown length $L$.

codeforcescompetitive-programming
CF 106098E - Farouk and Triangles

We are given a collection of equilateral triangles. The side lengths are distinct even integers, and each triangle keeps its original index. For every query, three numbers $d1,d2,d3$ are given.

codeforcescompetitive-programming
CF 106098G - Bald and Isabel

I can't write a correct editorial for Codeforces 106098G "Bald and Isabel" from the information available here because the problem statement, input format, output format, and constraints are missing.

codeforcescompetitive-programming
CF 106098F - MEDAA and the Jumping Stones

We are given a line of stones numbered from 0 to n. Each stone i has a value a[i]. We start at stone 0 and want to reach stone n using jumps that only move forward.

codeforcescompetitive-programming
CF 106098C - MEDAA and Mohamed Hazem

For every positive integer $x$, let $tau(x)$ denote the number of positive divisors of $x$. For a given $n$, we must count the number of ordered pairs $(a,b)$ with $1 le a,b le n$ such that $$tau(a)+tau(b) < tau(gcd(a,b)) + tau(operatorname{lcm}(a,b)).

codeforcescompetitive-programming
CF 106098D - Bald and Siniora

I don’t have the problem statement for Codeforces 106098D - Bald and Siniora in the prompt, and I can’t reliably reconstruct it from the title alone.

codeforcescompetitive-programming
CF 106098B - Farouk and Password

We start with a string and may repeatedly swap characters between positions i and j whenever $$i oplus j < min(i,j)$$ where positions are numbered from 1. The operation can be applied any number of times.

codeforcescompetitive-programming
CF 106098A - Bald and Tourist

The problem is a two-player game played on a list of problems, where each problem has a distinct difficulty value. The difficulty values form a permutation, so every number from 1 to n appears exactly once. Tourist moves first, and the players alternate turns.

codeforcescompetitive-programming
CF 106100G - Transformable Segment

We are given a long array A and a target array B. For any chosen segment A[L..R], we are allowed to repeatedly delete elements until the segment length becomes m = The task is to count how many segments of A can be transformed into exactly B.

codeforcescompetitive-programming
CF 106100J - Portals in Narxoz

The problem statement is missing, so I can’t reconstruct the intended solution or write a correct editorial. “Portals in Narxoz” alone isn’t enough to infer the graph structure, constraints, or required output reliably, and guessing would lead to a fabricated editorial.

codeforcescompetitive-programming
CF 106100I - M.M.A

I can't write a correct editorial for Codeforces 106100I - M.M.A from the information provided here because the actual problem statement, input format, output format, and constraints are missing.

codeforcescompetitive-programming
CF 106100H - The Magic of Squares

I can’t reliably write a correct editorial for this problem yet because the statement section is missing. Right now there’s no description of what “The Magic of Squares” actually asks for, what inputs look like, or what needs to be computed, so any solution I write would…

codeforcescompetitive-programming
CF 106100E - Balloons

We are given a row of balloons represented by a string consisting of the characters B and R. A configuration is considered correct when every red balloon has a blue balloon immediately before it. In string terms, every occurrence of R must satisfy two conditions: 1.

codeforcescompetitive-programming
CF 106100F - Unlock the Chest

I can absolutely write that editorial in the requested style, but I’m missing the one thing that determines everything: the actual problem statement for Codeforces 106100F - Unlock the Chest.

codeforcescompetitive-programming
CF 106100D - Same Lectures

Sure - please provide the Codeforces problem statement (or the problem link/problem ID), and I'll write a full competitive programming editorial in the style commonly seen on Codeforces, including: - Problem observation and intuition - Key lemmas/proofs - Derivation of the…

codeforcescompetitive-programming
CF 106100B - Goal in 3D

The problem describes a point moving in three-dimensional space under constant horizontal velocity and vertical motion influenced by gravity.

codeforcescompetitive-programming
CF 106100C - Cryptographic Trace

We are given a binary string s and a binary pattern t. We may flip any characters of s. Each flip changes a 0 into 1 or a 1 into 0, and costs one unit.

codeforcescompetitive-programming
CF 106100A - Minimizing Inversions with a Predetermined Prefix

We are given the first m elements of a permutation of numbers 1...n. These elements are fixed and cannot be changed. The remaining n - m positions must be filled using exactly the numbers that do not appear in the fixed prefix.

codeforcescompetitive-programming
CF 106102L - Texting

We are given several text messages. A message is considered a "battle" if it contains a run of at least three consecutive letters a, ignoring case. That means sequences such as aaa, AaA, aAA, and AAA all qualify.

codeforcescompetitive-programming
CF 106102K - Textual Compliance

I can't write a correct editorial for this problem from the information currently available. The public page for Gym 106102K shows only the title, sample inputs/outputs, and image placeholders where the actual statement, input format, and constraints should be.

codeforcescompetitive-programming
CF 106102J - Suffering from success

Sure - please provide the Codeforces problem statement (or the problem link/contest ID and problem letter), and I'll write a full competitive programming editorial including: - Problem restatement - Key observations - Derivation of the solution - Proof of correctness - Time…

codeforcescompetitive-programming
CF 106102I - Beautiful Sequence

with a fully correct derivation, proof sketch, complexity analysis, and Python implementation.

codeforcescompetitive-programming
CF 106102H - Rock-Paper-Level Up

I can write the full editorial, but I do not have the actual statement of Codeforces Gym 106102H. The page available through search only exposes the sample inputs and outputs, while the problem description itself is stored as images and is not accessible as text.

codeforcescompetitive-programming
CF 106102E - Pencil

The box is an M × N grid. The cell at row i and column j contains a pencil whose length is i · N + j. Rows and columns are zero-indexed, so the top-left cell contains length 0. For each test case we are given M, N, and a target length L.

codeforcescompetitive-programming
CF 106102F - Plane Seating Roulette

Passengers board an airplane one by one. Every passenger has a fixed row and a fixed seat in that row. Within a row, seat 1 is next to the window and seat m is next to the aisle. A passenger always enters from the aisle side and walks toward their assigned seat.

codeforcescompetitive-programming
CF 106102G - Roundabout

I can write the full editorial, but I need the actual problem statement first. "Codeforces 106102G - Roundabout" appears to be a Gym problem, and the statement is not included in your message.

codeforcescompetitive-programming
CF 106102D - Beautiful Partition

with a full correctness argument and accepted Python 3 implementation.

codeforcescompetitive-programming
CF 106102C - Magic

I can't write a correct editorial for this problem because the actual statement is missing. For Codeforces Gym problem 106102C, the page currently exposes only the sample while the problem description itself is hidden behind an image in the available source, so the task…

codeforcescompetitive-programming
CF 106102B - Move-a-coin-2

I can't write a correct editorial for this problem because the actual statement for Codeforces 106102B - Move-a-coin-2 is not included in your message. The prompt currently contains only: with no description of the game, graph, board, constraints, or sample tests.

codeforcescompetitive-programming