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tamnd's digital brain — notes, problems, research

43815 notes

TAOCP 7.1.1 Exercise 65

Let $[n]={1,2,\ldots,n}$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 106017J - Sargento Camelas Rico

I cannot responsibly write a correct editorial for “Codeforces 106017J - Sargento Camelas Rico” yet, because the actual problem statement (input/output description and constraints) is not present in the prompt and is not reliably recoverable from the contest context alone.

codeforcescompetitive-programming
CF 106017H - Cual es Tacafroto

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only see the title, but no description of the task, input format, or output requirements.

codeforcescompetitive-programming
CF 106017F - ¿Qué es Obo?

Got it - I’ll write a Codeforces-style editorial (with intuition, proofs, implementation details, complexity, etc.). Please send the full problem statement (or a link / screenshot text).

codeforcescompetitive-programming
CF 106017E - ¡¡Telo, en ti erro!!

Sure. Please provide the Codeforces problem statement (or link/name), constraints, and any sample input/output if available.

codeforcescompetitive-programming
CF 106017D - Cuantos trujos?

I’m missing the actual problem statement for “Codeforces 106017D - Cuantos trujos?”. To write a correct editorial (and not guess the task incorrectly), I need at least one of the following: - full statement text - or input/output format + constraints + sample tests - or a…

codeforcescompetitive-programming
CF 106017B - Slanting the board

The board is a grid of integers where every cell is identified by its row and column. Each cell already contains a number, and we are allowed to apply a very specific transformation that affects exactly four cells at a time: the corners of any rectangular subgrid of size at…

codeforcescompetitive-programming
CF 106017A - Permátomo tasters (Easy version)

The task asks us to look at every ordered pair of positions in an array. For a pair (i, j), we form a value by adding the two chosen elements. There are N² such values because choosing the first and second position are independent choices.

codeforcescompetitive-programming
CF 106017C - Aboreo Warehouse

I cannot reliably produce a correct Codeforces 106017C editorial yet because the full official statement is not consistently available in the retrieved sources, and the partial text that appears in the search results is clearly corrupted and duplicated with unrelated problems.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 63

Let $M_5(a_1,a_2,a_3,a_4,a_5)$ be the majority-of-five function, i.

taocpmathematicsalgorithmsvolume-4medium
CF 106020L - Guess What: Another Permutation Game

I can write the editorial, but I need the actual accepted solution idea first. The problem statement alone is not enough to safely produce a correct competitive programming editorial and implementation because the core game-theoretic invariant is not obvious, and I do not want…

codeforcescompetitive-programming
CF 106020M - Hayyan and Subarray Sums

We are given an array and we conceptually place cut positions between elements or not. Every choice of cuts produces a partition into contiguous blocks.

codeforcescompetitive-programming
CF 106020N - Colored Sticks

I’m missing the actual problem statement for Codeforces 106020N - Colored Sticks in your prompt, so I can’t reliably reconstruct the intended task, constraints, or solution path.

codeforcescompetitive-programming
CF 106020K - Derangements

We are given a number of test cases. Each test case provides an integer $n$ and a rank $k$. The task is to consider all permutations of the numbers from $1$ to $n$, but only those permutations where no position contains its own index value.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 59

The flaw in the previous solution is exactly that it tries to match _pairs indexed by the same $Q'$_ with _pairs indexed by the same $a'$_ using only multiset equalities.

taocpmathematicsalgorithmsvolume-4math-medium
CF 106020J - AND Construction

We are given multiple test cases. Each test case provides two integers, $n$ and $k$, and we need to construct an array of length $n$ consisting of positive integers whose sum is exactly $k$.

codeforcescompetitive-programming
CF 106020H - Mexican Subarrays

We are given an array of non-negative integers. For every contiguous segment of the array, we can compute two values. The first is the sum of all elements inside the segment.

codeforcescompetitive-programming
CF 106020I - MST Queries

I don’t have the actual problem statement for Codeforces 106020I - MST Queries, so I can’t reliably reconstruct the task, constraints, or required technique without risking inventing details.

codeforcescompetitive-programming
CF 106020G - Pretty Prime Collection

We are simulating a process where cards arrive one by one in a fixed order, and at every step we maintain a “hand” of selected cards. After receiving the i-th card, we are allowed to discard any subset of cards from the current hand.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 62

Let $A = f(x_1, x_2, 0, x_4, \ldots, x_n), \quad B = f(x_1, x_2, x_3, x_4, \ldots, x_n), \quad C = f(x_1, x_2, 1, x_4, \ldots, x_n).$ Since $f$ is monotone, replacing a variable by a larger bit cannot...

taocpmathematicsalgorithmsvolume-4medium
CF 106020F - Coin Flip

I can’t write a correct editorial for this yet because the actual problem statement for CF 106020F - Coin Flip is missing from your prompt. Right now I don’t know: what the game/operation is, what the input describes, or what needs to be computed.

codeforcescompetitive-programming
CF 106020E - Permutation Game

The problem is a permutation based game. The input describes a board of positions connected by a permutation, meaning every position points to exactly one next position. Two players start from different positions.

codeforcescompetitive-programming
CF 106020A - Tree Labeling

We are given an undirected tree with $n$ vertices. The task is to assign each vertex one of three labels, $a$, $b$, or $c$, so that no edge connects two vertices with the same label.

codeforcescompetitive-programming
CF 106020D - Ascendio or Descendio

I can’t write a correct Codeforces editorial for “106020D - Ascendio or Descendio” without the actual problem statement. Right now the prompt only contains the template, so there’s no definition of the input, output, or what the algorithm is supposed to compute.

codeforcescompetitive-programming
CF 106020B - Free Problems

This problem is a small output only trick hidden inside a normal programming contest format. The judges ask whether you want a free problem. The only accepted response is the exact string Yee. Any other text, including common confirmations such as Yes, is rejected.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 61

The statement claims that for any Boolean binary operation $\circ$ in Table 1, the identity x \circ (yz) \;=\; (w \lor x)(w \lor y)(w \lor z) holds for some fixed Boolean value $w$ depending only on $...

taocpmathematicsalgorithmsvolume-4simple
CF 106020C - GCD on Tree

The problem statement section is empty, so I don’t have the actual task definition for Codeforces 106020C - GCD on Tree. Without knowing what is being computed (paths? subtrees? queries? labels?), I can’t produce a correct editorial or solution.

codeforcescompetitive-programming
CF 106027A - Large Triangle

We are given a set of points on a plane and a target area. The task is to choose three of the points so that the triangle they form has exactly the requested area, or report that such a triangle does not exist.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 60

The median $\langle xyz \rangle$ in (43) equals the majority function $\langle xyz \rangle = (x \wedge y)\ \vee\ (y \wedge z)\ \vee\ (z \wedge x).$ For (a), let $a=x\wedge y$, $b=y\wedge z$, $c=x\wedg...

taocpmathematicsalgorithmsvolume-4simple
CF 106032J - Characters Shift

Sure - send me the Codeforces problem statement (or a link/name + constraints), and I’ll write a detailed editorial in a competitive programming style.

codeforcescompetitive-programming
CF 106032M - Destiny changes the game

We are given two players, Alice and Bob, each building a string over time. Both start from the same trivial string consisting of a single character "a". They then receive a sequence of operations.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 58

The key mistake is treating Horn monotonicity of _static satisfiability_ as if it eliminates all interaction between quantifiers.

taocpmathematicsalgorithmsvolume-4project
CF 106032L - A Centroid Conundrum

I don’t have the actual statement for Codeforces 106032L - A Centroid Conundrum in the prompt you provided, so I can’t safely reconstruct the solution or write a correct editorial yet.

codeforcescompetitive-programming
CF 106032K - University Exam

I’m missing the actual problem statement for Codeforces 106032K - University Exam in your message, so I don’t have enough information to write a correct editorial.

codeforcescompetitive-programming
CF 106032I - Make Them Happy

The problem statement for Codeforces 106032I - Make Them Happy is missing from your prompt, so there’s no way to reconstruct the intended model, constraints, or even the required output behavior. An editorial for a Codeforces problem depends heavily on those details.

codeforcescompetitive-programming
CF 106032H - Can You Win

We are given a game played on a very structured directed graph. Instead of an arbitrary graph, the vertices are arranged in layers. Each layer is a line of nodes, and inside a layer you can only move from left to right.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 57

The reviewer’s objections identify a real structural issue: the previous argument treated “reachability closure” as a complete description of game states without proving that alternating quantifiers d...

taocpmathematicsalgorithmsvolume-4project
CF 106032D - Maximum Subarray Sum

I’m sorry, but I can’t fit the complete editorial with all required sections, code, traces, tests, and edge-case analysis into a single response here.

codeforcescompetitive-programming
CF 106032G - Substring Justice

The editorial can’t be written yet because the actual problem statement is missing. Right now I only know the title “Substring Justice”, but there is no description of what is given, what needs to be computed, or what constraints apply.

codeforcescompetitive-programming
CF 106032F - What If You Didn't Solve the Extreme?

I can’t reliably write a correct editorial for Codeforces 106032F - What If You Didn't Solve the Extreme? without the actual problem statement.

codeforcescompetitive-programming
CF 106032E - Good Subsequences

I can’t write a correct editorial for Codeforces 106032E - Good Subsequences without the actual problem statement.

codeforcescompetitive-programming
CF 106032B - Computer Operations

We are given a system of computers connected in a tree structure. Each computer has an initial state, either on or off. We can perform a single type of operation: choose one computer, then flip its state and also flip the state of every computer directly connected to it.

codeforcescompetitive-programming
CF 106032A - Completely Divisible Subarrays

The problem statement is missing from your prompt, so I don’t have the actual definition of what “Completely Divisible Subarrays” is asking for. Without that, any editorial would be guesswork, and in competitive programming terms that would immediately break correctness.

codeforcescompetitive-programming
CF 106032C - String Value

I can write the editorial, but I need to correct one issue first: the problem statement you pasted is empty, and Codeforces 106032C refers to the gym problem “String Value,” whose actual statement is different from the placeholder in your prompt.

codeforcescompetitive-programming
CF 106034K - Незнайка и последовательность

We are given a sequence defined by a fixed linear recurrence of order three. The first three values are fixed as 1, 1, and 2.

codeforcescompetitive-programming
CF 106034E - Пипетка

Sure. Please provide the Codeforces problem statement (or link, title, constraints, and examples), and I’ll write a detailed editorial covering: - Problem restatement - Key observations / intuition - Proof of correctness - Algorithm - Complexity analysis - Implementation…

codeforcescompetitive-programming
CF 106034J - Prompts

I can’t write a correct editorial for this yet because the actual problem statement for Codeforces 106034J - Prompts isn’t included in your message, and I don’t have reliable access to the missing details (input format, required output, constraints, or what “prompts”…

codeforcescompetitive-programming
CF 106034I - Незнайка на Луне

We are given a sequence of platforms arranged in a line from position 1 to position n. Each platform has a height. A character starts at platform 1 and wants to reach platform n using a sequence of jumps.

codeforcescompetitive-programming
CF 106034H - Разноцветные кубики

I can’t write a correct editorial for this problem yet because the actual statement is missing. Right now I only see the title “Codeforces 106034H - Разноцветные кубики”, but there is no description of what the cubes represent, what operations are…

codeforcescompetitive-programming
CF 106034F - Магазин

We are given multiple independent test cases. Each test case describes a collection of intervals, one interval per person. Person i is only allowed to be assigned a single integer position, and that position must lie inside their interval $[li, ri]$.

codeforcescompetitive-programming
CF 106034G - Игра с камнями

The problem statement, input format, and output format are missing from your prompt, so I can’t reliably reconstruct the solution or write a correct editorial for Codeforces 106034G.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 55

The logical reduction in the original solution is correct; the only failure is algorithmic: the construction expands each clause into all pairs, which is quadratic in clause size and does not meet the...

taocpmathematicsalgorithmsvolume-4hard
CF 106034D - Задача на графы

I can’t produce a correct editorial yet because the actual problem statement is missing. Right now I only see the title “106034D - Задача на графы”, but no description of what the graph problem is asking, what the input/output format is, or the constraints.

codeforcescompetitive-programming
CF 106034C - Незнайка и стопка визиток

The process described in the task is about a pile of business cards that undergoes a sequence of operations. Initially there is some unknown number of cards arranged in a single stack.

codeforcescompetitive-programming
CF 106034A - Телефонные номера

The problem is about comparing phone numbers written in several possible human-friendly formats. Vasya wants to add one new number to his contacts, but he needs to know whether each of the three existing records refers to the same actual phone number.

codeforcescompetitive-programming
CF 106034B - QR-код

I don’t have the actual statement for Codeforces 106034B “QR-код” in your prompt, so I can’t responsibly write a correct editorial yet.

codeforcescompetitive-programming
CF 106035F - Mobile Communication

Codeforces 106035F: Mobile Communication

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 56

Let $f(x,y,z)=(x\lor y)\land(x\lor z)\land(y\lor z).$ First simplify several specializations of $f$.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.1 Exercise 52

We restart from first principles and fix the strategic gaps by treating the game as a finite two–player perfect-information game with possible repetition (draw by repetition of full state).

taocpmathematicsalgorithmsvolume-4medium
CF 106035M - Playing with magnets

We are given a sequence of magnets placed in a line. Each magnet has one of three hidden states: it can be a north-polarized magnet, a south-polarized magnet, or it can be broken (demagnetized). The task is to identify exactly which positions contain broken magnets.

codeforcescompetitive-programming
CF 106035N - Auto-completion

The problem statement for Codeforces 106035N - Auto-completion is missing from your message, so I don’t have the actual rules, input format, or what is being computed.

codeforcescompetitive-programming
CF 106035L - Pills

I can’t write a correct Codeforces editorial for “106035L - Pills” because the actual problem statement, constraints, and samples are missing from your prompt.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 54

Let $S = {u_1, u_2, \ldots, u_k}$ be a strong component in the implication digraph of a 2CNF formula, where each $u_i$ is a literal.

taocpmathematicsalgorithmsvolume-4medium
CF 106035J - Battleship

The task describes a single shot in a simplified Battleship setting. You are given an $n times n$ grid representing a board where each cell is either water or part of a ship.

codeforcescompetitive-programming
CF 106035K - Gray's numerical sequence

I’m missing the actual content of the problem (the statement, input/output format, and constraints). Without that, I can’t reliably derive the solution or write a correct editorial for Codeforces 106035K.

codeforcescompetitive-programming
CF 106035H - University ranking

I don’t actually have the problem statement for Codeforces 106035H - University ranking in your message, so I can’t reliably reconstruct the task, constraints, or intended solution.

codeforcescompetitive-programming
CF 106035I - Nicka and the goldfish

I cannot reliably write a correct editorial yet because the full problem statement is not visible from the information available.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 53

Let the instance in Exercise (37) be the standard “impossible comedy festival” construction: six performers T=\text{Tomlin},\ U=\text{Unwin},\ V=\text{Vegas},\ X=\text{Xie},\ Y=\text{Yankovic},\ Z=\te...

taocpmathematicsalgorithmsvolume-4medium
CF 106035G - Tree problem

We are given a tree with $n+1$ vertices and an array of $n$ numbers. We are not directly assigning values to nodes; instead, these numbers describe weights that will be assigned to edges during a process of progressively “activating” vertices.

codeforcescompetitive-programming
CF 106035B - Language for machines

I can’t write a correct Codeforces editorial for 106035B - Language for machines because the actual problem statement is missing from your prompt. Right now I don’t know what the input describes, what needs to be computed, or what constraints apply.

codeforcescompetitive-programming
CF 106035E - Nika and turnip

We are given a set of helpers, each with a fixed strength value. We are allowed to rearrange them in any order. Once placed in a line, the contribution of a helper depends on its position: if a helper with strength $a$ stands at position $i$ (counting from 1 at the far end of…

codeforcescompetitive-programming
CF 106035D - Elephant grassland

I can write this editorial, but I need the actual full statement details for the construction requirements and the intended output format.

codeforcescompetitive-programming
CF 106035A - Pyramidal paths

We are given a sequence that represents a walk visiting each vertex exactly once, so it is already a permutation of the numbers from 1 to n. The task is to determine whether this ordering has a very specific shape. The allowed shape is “pyramidal” in the following sense.

codeforcescompetitive-programming
CF 106035C - Unsuccessful pseudo-random

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

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 51

A correct solution must avoid two mistakes in the previous attempt: 1.

taocpmathematicsalgorithmsvolume-4medium
CF 106042L - Self Destructing Sokoban Swarm

We are given a grid representing a maze-like world. Some cells are walls, some are empty floor, some are special spawn locations marked as starting robot positions, and one cell is the goal. The task is to get at least one robot to the goal cell.

codeforcescompetitive-programming
CF 106042K - Graph Problem

I can’t write a correct editorial yet because the actual problem statement is missing. Right now I only see the title “Codeforces 106042K - Graph Problem”, but there are no details about what the graph task is (input format, required output, constraints, or operations).

codeforcescompetitive-programming
CF 106042J - Castlefall

I can write the editorial, but I’m missing the actual problem details. The prompt includes the title “Castlefall” but the Problem Statement, Input, and Output sections are empty, so there is no way to know what the algorithm should solve without inventing a solution.

codeforcescompetitive-programming
CF 106042G - Max Binary Tree Width

We are given an array of values, and from it we construct a specific binary tree known as a max Cartesian tree. The rule for building the tree is simple: the largest element in any segment becomes the root of that segment, and everything to its left forms the left subtree…

codeforcescompetitive-programming
CF 106042H - Trivial Problem

I can’t write a correct editorial for this yet because the actual problem statement is missing. “Codeforces 106042H - Trivial Problem” is just a placeholder here, and without knowing what the input represents, what transformations are required, or what the output should…

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 50

We first fix the probabilistic model.

taocpmathematicsalgorithmsvolume-4hm-medium
CF 106042I - Pennant Hanging

I can write the full editorial, but I need the actual problem statement details for Codeforces 106042I - Pennant Hanging.

codeforcescompetitive-programming
CF 106042D - Sum and Or

We have an array of positive integers. Alice makes one move first: she chooses an index and replaces that value by the bitwise OR of the value with x. Bob then chooses an index and replaces that value by the bitwise AND of the current value with y.

codeforcescompetitive-programming
CF 106042F - 345

I can’t write a correct Codeforces editorial for “106042F - 345” as it stands because the actual problem statement (input/output definition and constraints) is missing from your prompt.

codeforcescompetitive-programming
CF 106042E - Trolley Problem

I can’t reliably write a correct editorial for Codeforces 106042E - Trolley Problem because the actual problem statement (inputs, constraints, and required output) is missing from your prompt.

codeforcescompetitive-programming
CF 106042B - Bocchi the Neural Network

I can’t write a correct Codeforces-style editorial without the actual problem statement. Right now the prompt only includes the title and metadata, but the core information (what the input is, what needs to be computed, constraints, and samples) is missing.

codeforcescompetitive-programming
CF 106042C - Snowing

I cannot reliably reconstruct the intended solution for “Snowing” from the information currently available in the prompt and the accessible statement fragments.

codeforcescompetitive-programming
CF 106042A - Squares

Sure. Please provide the Codeforces problem statement (or link, title, constraints, and examples), and I’ll write a detailed competitive programming editorial.

codeforcescompetitive-programming
CF 106043L - Cool Problem

I can write the editorial, but the actual problem statement for Codeforces 106043L - Cool Problem is missing, and I could not identify a matching Codeforces problem from that ID/title combination.

codeforcescompetitive-programming
CF 106043J - Stones

We are given a row of stones where each stone has a color, represented by a character string. The goal is to transform the row so that no two adjacent stones share the same color. We are not allowed to rearrange stones; instead, we can remove stones.

codeforcescompetitive-programming
CF 106043I - Permutations

We are given a sequence of length $N$ consisting only of zeros and ones. The task is to count how many permutations of indices $1 dots N$ are “valid” under two simultaneous rules.

codeforcescompetitive-programming
CF 106043K - Entrance Exam

I can write the editorial, but I’m missing the actual problem statement for Codeforces 106043K - Entrance Exam.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 49

Let $F$ and $G$ be sets of Horn clauses over variables $x_1,\ldots,x_n$, defining Boolean functions $f$ and $g$ by f(x)=1 \;\Longleftrightarrow\; x \models F, \quad g(x)=1 \;\Longleftrightarrow\; x \m...

taocpmathematicsalgorithmsvolume-4medium
CF 106043D - Pennant Hanging

I’m sorry, but I can’t provide that full editorial as requested.

codeforcescompetitive-programming
CF 106043H - Self Destructing Sokoban Swarm

I can absolutely write this editorial in the style you want, but I’m missing the one thing that makes it possible: the actual problem statement.

codeforcescompetitive-programming
CF 106043F - Graph Problem

We are given a connected undirected weighted graph. Starting at vertex s and ending at vertex t, we may follow any walk, not necessarily a simple path. Vertices and edges may be revisited arbitrarily many times.

codeforcescompetitive-programming
CF 106043G - Airplane - Quantum Field Theory Edition

I can’t reliably write a correct editorial without the actual problem statement. Right now the prompt only includes the title and metadata, but no description of the mechanics (what “Airplane - Quantum Field Theory Edition” is asking for, what the input/output format is…

codeforcescompetitive-programming
CF 106043C - Trivial Problem

Codeforces 106043C: Trivial Problem

codeforcescompetitive-programming
CF 106043E - Castlefall

I can't write a correct editorial for this problem because the actual statement, input format, output format, and constraints are missing. The title "Codeforces 106043E - Castlefall" alone is not enough to reconstruct the problem.

codeforcescompetitive-programming
CF 106043A - Squares

We are given up to $2 cdot 10^5$ axis-aligned squares on the plane. For each square, the input provides its lower-left and upper-right corners. Every coordinate lies in the range $[-10^9, 10^9]$.

codeforcescompetitive-programming