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tamnd's digital brain — notes, problems, research

43815 notes

CF 106082G - Which Number

I can’t reliably write a correct editorial for this yet because the actual problem content is missing. What you provided only includes the title (“Which Number”) and a tag (“maxsat”), but none of the real statement, constraints, or input/output definition.

codeforcescompetitive-programming
CF 106082D - Pseudo Pseudo Random Numbers

I can’t reliably write a correct Codeforces editorial for “106082D - Pseudo Pseudo Random Numbers” from the information provided, because the actual problem statement (inputs, operations, and required output) is missing.

codeforcescompetitive-programming
CF 106082A - Number Maximization

I can’t write a correct editorial without the actual problem statement. Right now, the input/output section is empty, and “Number Maximization” alone isn’t enough to reliably reconstruct the task.

codeforcescompetitive-programming
CF 106084I - Reactor

We are managing a line of reactors, each one behaving like a small system with two internal values: a current pressure and a maximum pressure threshold. Initially every reactor has zero pressure, while each position starts with its own threshold value.

codeforcescompetitive-programming
CF 106084F - Fruitful Compression

We are given a 4 by 4 Latin square over four symbols representing fruits, except that some cells are already empty. The valid full configuration is always a Latin square: every row and every column contains each of the four fruits exactly once.

codeforcescompetitive-programming
CF 106084B - Twin Guardians

We are given several independent queries. Each query contains two integers, and we need to decide whether these two numbers form a pair of twin primes.

codeforcescompetitive-programming
CF 106503K - NTT

We are given a polynomial described by its coefficients in increasing order of degree. In other words, the input defines a function F(x) = f0 + f1 x + f2 x^2 + ...

codeforcescompetitive-programming
CF 106494E - Dark Labyrinth

We are working with a graph where the process starts from a single distinguished vertex, initially vertex 1, and we maintain a dynamically growing set of vertices, called $c$. Conceptually, $c$ is always treated as a single “compressed” component.

codeforcescompetitive-programming
CF 106486F - 送熏肉

We are given a long sequence of levels, each level carrying a difficulty value. The player can remove exactly one contiguous block of fixed length $k$, and everything outside that block remains and contributes to the total difficulty.

codeforcescompetitive-programming
CF 106484H - Teaching Building

We are given a rooted tree with vertices labeled from 1 to 2n, rooted at 1. Each vertex represents a “teaching area” that must appear as a connected region inside a grid of size (n+1) by (2n). Each cell of the grid either contains 0 or one of the labels 1 through 2n.

codeforcescompetitive-programming
CF 106467D - Left & Right

I can write the full Codeforces-style editorial, but I’m missing the actual problem content. Right now, “Codeforces 106467D - Left & Right” in your prompt does not include the statement, constraints, or samples, so I cannot reconstruct the intended solution or guarantee…

codeforcescompetitive-programming
CF 106461H - How to Validate Such a Program

We are given a tree, but we do not directly work with edges. Instead, we are given access to its distance matrix, where entry $D{i,j}$ stores the length of the unique path between vertices $i$ and $j$.

codeforcescompetitive-programming
CF 106456A - Your Shine Your Be!

We are given an array of non-negative integers. Each query asks about a subarray defined by a range, but the actual range is not given directly.

codeforcescompetitive-programming
CF 106444L - Ynoalgoget

The task revolves around counting contributions of certain structured binary strings that are implicitly generated by a process that walks along a fixed “main string” and records how far it can match prefixes while extending.

codeforcescompetitive-programming
CF 106444E - Jsteyki

The problem defines a notion of a “level” where movement between tiles follows chess bishop-like behavior, and each pair of tiles has an associated minimum time required to move between them.

codeforcescompetitive-programming
CF 106443K - K-Places

A group of N participants wants to visit tourist spots numbered from 1 to K. Each participant comes with a list of places they refuse to visit.

codeforcescompetitive-programming
CF 106443A - Amusing Enhancements

We are asked to count how many different ways we can build a sequence of participants whose individual contributions to a “fun score” add up exactly to a given target value $D$. Each participant contributes either 1 unit of fun in a normal state or 2 units if enhanced by AI.

codeforcescompetitive-programming
CF 106440K - 共享单车

We are simulating a commuter who travels over a sequence of days, where each day requires access to a bike from one or both of two providers.

codeforcescompetitive-programming
CF 106440E - 周长

We are given a weighted grid. Each cell has a positive value, and we want to select a simple closed shape drawn along grid edges. The shape must not self-intersect and must form a single closed loop. The region enclosed by this loop is a connected set of unit cells.

codeforcescompetitive-programming
CF 106435A - Странная фигура

We are given a construction that starts with a square and then repeatedly places additional squares inside it. Each new square is rotated by 45 degrees relative to the previous one, so the whole picture becomes a nested system of overlapping diagonals and edges rather than a…

codeforcescompetitive-programming
CF 106434D - Опять эта математика

We are given a list of positive integers. From this list, we conceptually form every unordered pair of distinct elements. For each pair, we compute the least common multiple of the two numbers, producing a very large multiset of values.

codeforcescompetitive-programming
CF 106430K - Bessie and Heist

We are given a circular structure with n positions, each carrying a value. A process is defined where we choose a “step size” d, and then repeatedly jump around the circle by adding d modulo n.

codeforcescompetitive-programming
CF 106430E - Bessie and Groups

We are given an array that is partitioned into consecutive groups of fixed size, and the task is to determine whether the structure can be rearranged into a globally sorted order under constraints that preserve group structure.

codeforcescompetitive-programming
CF 106429E - Snake

We are simulating a process where a snake moves through a fixed sequence of cells over time. At each time step $t$, the head of the snake occupies a known cell $c(t)$. Some cells may repeat over time, meaning the snake can revisit the same position later.

codeforcescompetitive-programming
CF 106420D - Anagrams

We are given a very small multiset of characters, and we are asked to consider every distinct string that can be formed by rearranging some or all of those characters.

codeforcescompetitive-programming
CF 106416J - Jaime's Palace

We are given a system that repeatedly manipulates a stack of plates. There are P distinct plates, initially arranged in a stack. Over D days, each day specifies a number Ki.

codeforcescompetitive-programming
CF 106416D - Dropshipping

We are given a sequence of purchase requests, each associated with a cost. Every request must be satisfied exactly once, and satisfying a request corresponds to making one purchase of that item at its full listed price.

codeforcescompetitive-programming
CF 106398J - Призрачная очередь

We are given a line of spirits standing in a queue, each with an initial height. Two observers look at this queue from opposite ends, but each of them has a very specific visibility rule.

codeforcescompetitive-programming
CF 106398B - Утренняя песня хомяков

We are given a long uppercase string that represents a recording of a choir performance. Each hamster in the choir has a unique “song”, and each song is exactly two characters long.

codeforcescompetitive-programming
CF 106396J - 湖中回眸

We are given two binary grids of the same size, each cell containing a value that can be interpreted as either 0 or 1. The task is to transform the first grid into the second grid using a specific type of operation: choosing a cell (or position) and flipping its value.

codeforcescompetitive-programming
CF 106396A - 狼

We are given a collection of items, each with an integer weight. There is also an initial offset value, which behaves like a starting balance in the system. The process begins from this offset, and each item can be chosen at most once.

codeforcescompetitive-programming
CF 106393A - Сильнейшая команда

We are asked to select exactly k characters from a pool of n, maximizing total strength, but the choice is restricted by two independent classification rules derived from each character’s attributes. Each character has a value ci which we want to maximize in sum.

codeforcescompetitive-programming
CF 106387E - Feed the Beast

We are given a system of multiple buildings, each associated with a production rate. Time progresses in discrete days, and as time increases, each building accumulates demand for “food boxes” according to its own rate.

codeforcescompetitive-programming
CF 106384A - 秘源机兵统御械 - 疾攻

The statement you provided is effectively empty. It only contains the problem title “秘源机兵统御械 - 疾攻” and no description of the input, output, constraints, or rules of the task. A Codeforces editorial depends entirely on those details.

codeforcescompetitive-programming
CF 106353K - KIT Finding

We are given a rectangular grid of size $h times w$. Every cell must be filled with one of three letters: ‘K’, ‘I’, or ‘T’. The counts of these letters are fixed in advance, so the grid is essentially a multiset of characters that must be arranged into a matrix.

codeforcescompetitive-programming
CF 106339E - Snowfake

We are given a set of points on a triangular lattice defined by two basis vectors, typically denoted $e1$ and $e2$. Every point in the input is expressed as an integer combination $u cdot e1 + v cdot e2$.

codeforcescompetitive-programming
CF 106328I - Operating System

We are given two parameters, a value limit m and a window size k. We must construct a sequence a, where each element is between 1 and m, such that a certain process produces different results when the window size is k versus when it is k+1.

codeforcescompetitive-programming
CF 106252M - The End?

We are given 8 teams, and we must arrange them into a fixed single-elimination bracket with 8 seed positions. The bracket structure is completely predetermined: seeds 1 vs 2, 3 vs 4, 5 vs 6, 7 vs 8 in the first round, then winners of (1-2) play winners of (3-4), and winners of…

codeforcescompetitive-programming
CF 106250H - Snacks Scheduling

We are given an array of length $N$, where each position $i$ is associated with a forbidden value $Ai$. The task is to construct a permutation $P$ of numbers $1$ to $N$ such that no position matches its forbidden value, meaning $Pi ne Ai$ for every index $i$.

codeforcescompetitive-programming
CF 106241O - Ya Masa2 El Geometry

We are given a set of points on a plane, and the task is to cover all of them using at most two circles. Each circle can be placed anywhere and can have any radius, including zero.

codeforcescompetitive-programming
CF 106239E - 质数变化

We are given multiple independent queries. Each query provides two prime numbers, both strictly less than 10000, and we treat them as four-digit numbers by padding with leading zeros when necessary.

codeforcescompetitive-programming
CF 106225L - LFS

We are given a long string representing a sequence of enemy types in a game level. Each query selects a contiguous segment of this string, and for that segment we must measure how repetitive its internal substrings can be.

codeforcescompetitive-programming
CF 106208J - Insert Force

We start with a sequence of non-negative integers. Each move picks two adjacent elements, adds their sum to a running score, and inserts that same sum back into the array between those two elements.

codeforcescompetitive-programming
CF 106202H - Головоломка отрезков

Each item in this problem is a key that has a rigid base length and a single protruding segment somewhere along that base. When a key is placed, its base contributes to a growing horizontal line, because all chosen keys are concatenated in some order without gaps.

codeforcescompetitive-programming
CF 106201D - Не доверяйте свиткам

We are dealing with three arrays of equal length, representing daily expenses split into food, equipment, and tavern spending. For the original data, every day has the same total spending across all three categories.

codeforcescompetitive-programming
CF 106200B - Математика для Зеркала

We are given a geometric progression defined by its first term and ratio. Concretely, the sequence is A: q, q·r, q·r², q·r³, and so on, continuing infinitely.

codeforcescompetitive-programming
CF 106199C - Полиция 2099

We are given a rooted tree of employees. Employee 1 is the root, and every other employee has exactly one direct manager with a smaller index, so the structure is a rooted tree. Each node carries a label, a single lowercase letter representing that employee’s specialty.

codeforcescompetitive-programming
CF 106194G - 猫猫虫困境III

We are working on an integer grid where each entity moves in discrete time under two competing forces: player-controlled movement and a deterministic attraction toward the origin.

codeforcescompetitive-programming
CF 106193I - Infection Investigation

We are given a permutation of numbers from 1 to n, which we can think of as a sequence placed along a line. For any query segment [l, r], we look only at the values inside that segment and ask for the length of the longest subsequence whose values strictly increase.

codeforcescompetitive-programming
CF 106192D - Подарок из Японии

The task is not a typical interactive or input-driven problem. Instead, the statement describes a solved Japanese crossword puzzle (a nonogram) that encodes a single hidden picture.

codeforcescompetitive-programming
CF 106185H - Parentheses

We are given a row of positions, each position holding a stamp labeled with either an opening or closing parenthesis. We do not take substrings in the usual sense. Instead, we build a sequence by walking along these positions.

codeforcescompetitive-programming
CF 106175H - SETI

We are given a prime number $p$ and a string that represents the output of a hidden numeric process applied to an unknown sequence of coefficients $a0, a1, dots, a{n-1}$, where each coefficient is an integer in the range $[0, p-1]$.

codeforcescompetitive-programming
CF 106384L - 笨蛋题

I can’t write a correct Codeforces editorial from this yet because the actual problem content is missing. What you provided only includes the title “笨蛋题” and no description, input format, output format, or constraints.

codeforcescompetitive-programming
CF 106384I - 古明地恋学生物

The problem content you provided only contains the title and no actual statement, input format, output format, or constraints.

codeforcescompetitive-programming
CF 106384H - 春日影 (MyGO!!!!! ver.)

The problem statement is effectively missing here. What you provided only contains the title, with no input/output description, constraints, or sample behavior to anchor a solution.

codeforcescompetitive-programming
CF 106384D - 繁星坠海

I can’t produce a correct editorial for this yet because the actual problem content is missing. Right now, “Codeforces 106384D - 繁星坠海” is provided without any statement, constraints, input/output description, or samples.

codeforcescompetitive-programming
CF 106353E - Erratic Lights

We are given a string of length $n$, where each position represents a light bulb colored red, green, or blue. The only operation available is to pick a bulb and “touch” it, which immediately resets its color to one of the three colors uniformly at random, independently of…

codeforcescompetitive-programming
CF 106289D - Cube

Codeforces 106289D: Cube

codeforcescompetitive-programming
CF 106270B - Boulevard of Broken Cars

Codeforces 106270B: Boulevard of Broken Cars

codeforcescompetitive-programming
CF 106252L - Leo

We are asked to build a fixed logic circuit over $n$ input nodes. Each input node carries one of four symbols: three colored signals $R, G, B$, and a special transparent signal $$ that behaves like an “empty” value.

codeforcescompetitive-programming
CF 106241G - Journey Around The World

We are given a nearly complete undirected graph on $n$ cities. Originally, every pair of cities had a road, so the graph was a clique. Then a small number of edges, at most 200, were removed.

codeforcescompetitive-programming
CF 106239K - 线段覆盖

We are given a sorted list of distinct points on a number line. The task is to cover all these points using at most $k$ segments, where a segment can be any interval $[a,b]$ and its cost is its geometric length $ A useful way to reframe the problem is to think of grouping points.

codeforcescompetitive-programming
CF 106208G - Awkward Nodes

We are working with a tree where every node is either normal or special. A walk is allowed to move along edges freely, but there is one asymmetry in how nodes behave during the walk: normal nodes can be revisited any number of times, while each special node can appear at most…

codeforcescompetitive-programming
CF 106202D - Скелеты, кости, кладбище, черепа

We are given a graph whose vertices are points on a plane, but the geometry only matters through the x-coordinates. Each edge connects two vertices, and an edge can be thought of as a straight segment, although crossings between segments do not allow traversal.

codeforcescompetitive-programming
CF 106194M - 如果是勇者辛美尔的话

We are given points placed on a circle, each point having an angle θ and an independent probability p of being “activated”. After activation, every triple of activated points forms a triangle, and all such triangles together act as a defensive region.

codeforcescompetitive-programming
CF 106194D - 寻找哈基米

The grid describes a city map where each cell is either free ground, an obstacle building, a street tile, or one of two special positions: the starting point and the target.

codeforcescompetitive-programming
CF 106193D - Defense Distance

We are asked to construct three non-empty strings over lowercase English letters such that the pairwise distances between them match three given integers.

codeforcescompetitive-programming
CF 106192G - Подарок на юбилей

We are given an array of integers. We are allowed to repeatedly apply a specific local operation on any adjacent pair. The operation takes two neighboring values, computes the bitwise AND of the pair, and then XORs that value into both elements.

codeforcescompetitive-programming
CF 106185D - Ancient Game Board

We are given a rectangular grid made of two colors, represented by . and . This grid is not arbitrary; it is assumed to be a fragment of a much larger infinite tiling. The hypothesized structure is a chessboard-like arrangement of identical square blocks.

codeforcescompetitive-programming
CF 106175G - Pipes

We are given a rectangular floor plan made of small square rooms arranged in an r by c grid. Between adjacent rooms there are walls, and each wall has a digit cost indicating how expensive it is to drill a pipe through that boundary.

codeforcescompetitive-programming
CF 106170A - Rainbow

We are given a tree with $n$ vertices. Each edge must be assigned a color from a palette $0$ to $K-1$, where $K$ is not fixed in advance and is part of what we are trying to maximize. Once edges are colored, we look at simple paths in the tree.

codeforcescompetitive-programming
CF 106167M - Monty's Hall

We are given a hall with $d$ doors. Exactly one door hides a prize, and all others are empty. The player is allowed to initially choose a group of $s$ doors instead of just one.

codeforcescompetitive-programming
CF 106167C - Card Trading

Each card type comes with a collection of buy and sell offers, each tied to a specific price level. A buy offer at price p means someone is willing to purchase at any market price up to p.

codeforcescompetitive-programming
CF 106164M - Merticulous Manipulation

We are simulating a very specific construction process that builds a permutation indirectly. Instead of being given the final arrangement of cards, we are told how the deck is built step by step, and we are asked to reverse engineer the decisions that would produce a desired…

codeforcescompetitive-programming
CF 106164A - Among Us

We are dealing with a hidden structure on a set of $N$ labeled crewmates. Each crewmate secretly points to exactly one other crewmate, and every crewmate is pointed to by exactly one person.

codeforcescompetitive-programming
CF 106161D - Deductive Snooker Scoring

We are given a target state of a simplified snooker-like scoring system. At any moment, there are two players, and one of them is currently at the table. We know the current scores of Player A and Player B, we know how many balls remain on the table, and we know whose turn it is.

codeforcescompetitive-programming
CF 106159N - Nautic Issue

We are given a motion process that starts from an unknown integer position $X$. From this starting point, a sequence of moves is executed.

codeforcescompetitive-programming
CF 106151G - windowmanager

We are given a collection of axis-aligned rectangles placed on a 2D plane, each representing a window. Every window also has a unique height value, which determines visibility: if two windows overlap, the one with higher height covers the other in the overlapping region.

codeforcescompetitive-programming
CF 106144H - Rigged Matchmaking

We are given two teams, each consisting of all athletes whose skill values form a contiguous integer segment. Monland has skills from $lM$ to $rM$, and Berland has skills from $lB$ to $rB$. One special athlete from Monland, the one with skill $lM$, is fixed as Monocarp.

codeforcescompetitive-programming
CF 106142H - Разделение на части

We are given a string composed of lowercase Latin letters. The task is to cut this string into several contiguous segments so that every character belongs to exactly one segment. Each segment must satisfy a strict structural constraint.

codeforcescompetitive-programming
CF 106141F - Arsen and Toy Soldiers

We are working with a lineup of n soldiers. Each soldier is associated with two assignments: one for the morning formation and one for the evening formation. Each assignment is a number between 1 and n representing a rifle type, except some entries are unknown and marked as −1.

codeforcescompetitive-programming
CF 106136H - Square the Circle

We are interacting with a hidden geometric shape centered at the origin. In each test case, the hidden object is either a circle or a square, both centered at $(0,0)$, and we can only probe it by asking whether specific integer lattice points lie inside it.

codeforcescompetitive-programming
CF 106130I - 运动世界校园

We are given a single probability value p, describing the success rate of one independent attempt to obtain a required result. A student has exactly three independent attempts. Each attempt either succeeds with probability p or fails with probability 1 - p.

codeforcescompetitive-programming
CF 106125G - Genealogy Gumbo

We are given a collection of parent-child relations written in the form “A, son of B”. Each statement says that person A has a single known father B.

codeforcescompetitive-programming
CF 106132G - Torque Transmission

We are given a directed network of gears connected by shafts. Each shaft transfers torque from one gear to another, but only a fraction of the incoming torque survives, determined by an efficiency percentage on that shaft.

codeforcescompetitive-programming
CF 106130K - 最不上升也不下降序列

We are asked to construct a permutation of the numbers from 1 to n. From this permutation we look at two classical subsequence measures: the length of the longest strictly increasing subsequence and the length of the longest strictly decreasing subsequence.

codeforcescompetitive-programming
CF 106130D - 序列重构(困难版)

We are interacting with a hidden permutation of length $n$, and our only way to learn about it is to submit test permutations of the same length. Each query gives a score equal to how many positions match the hidden permutation exactly.

codeforcescompetitive-programming
CF 106129H - Happy Hookup

We are given a directed graph where vertices represent train stations and edges represent one-way train connections. Two people start from two different stations, and each can travel along directed edges any number of times.

codeforcescompetitive-programming
CF 106129D - Demand for Cycling

We are given a simple orthogonal polygon, meaning its boundary is a closed cycle made only of horizontal and vertical segments, with no self-intersections. The vertices are listed in counterclockwise order, so walking through them traces the city boundary.

codeforcescompetitive-programming
CF 106129C - Congklak

We are given a row of $n$ holes, each containing some number of stones. The process we simulate is a repeated game played $t$ times. In each game, a single “hand” starts at hole 1 carrying exactly one stone and moves strictly from left to right.

codeforcescompetitive-programming
CF 106125A - Alto Adaptation

We are given a sequence of musical notes, each represented as an integer pitch. We are also given a fixed vocal range, defined by an inclusive interval from ℓ to h.

codeforcescompetitive-programming
CF 106125K - Koehandel

Two players are about to perform a single exchange based on sealed bids. One player, Old MacDonald, has already hidden a number of coins in a cup, and you know exactly how many coins that is, call it $c$. You also have $n$ coins available.

codeforcescompetitive-programming
CF 106124D - Dune Dash

We are given a set of points in the plane that represent checkpoints of a race route, but the order in which the runner visited them is lost.

codeforcescompetitive-programming
CF 106124K - km/h

We are simulating a driver moving through a sequence of road signs, where each sign either sets a specific speed limit or removes the current restriction and restores the original national speed limit.

codeforcescompetitive-programming
CF 106124H - Hidden Permutation

We are given a hidden permutation on positions $1 ldots N$. This permutation defines how a binary string of length $N$ is transformed: each step simply reorders the bits according to the permutation.

codeforcescompetitive-programming
CF 106124F - Follower Forensics

We are given a set of accounts. Each account already comes with two numbers: how many people it follows, and how many people follow it.

codeforcescompetitive-programming
CF 106124A - Arithmetic Adaptation

We are given a single integer s, and we need to split it into two integers a and b such that their sum equals s. Both a and b must be nonzero, and both must lie within the range of three-digit integers, meaning between −999 and 999 inclusive.

codeforcescompetitive-programming
CF 106118C - CK Chang's Shopping Spree

We are given a list of gadget prices and an initial amount of money. The buying rule is restrictive: before purchasing any gadget, the current amount of money must be at least ten times the price of that gadget. After buying it, the money is reduced by the gadget’s price.

codeforcescompetitive-programming
CF 106118N - Nobita's Homework! Help Me Doraemon

We are given three arrays of length n. The first two arrays define the boundary of an n by n grid. The first column is filled directly from the array a, the first row is filled from the array b, and the top-left cell is shared between them.

codeforcescompetitive-programming
CF 106118L - Label the Tree

We are given a rooted tree where vertex 1 is the root, and every other vertex has a fixed parent. On this tree we consider permutations of the vertices, meaning every vertex label from 1 to n appears exactly once in some order.

codeforcescompetitive-programming