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43815 notes

CF 105822E - Anti-Sorting Game

I don’t have the statement for Codeforces 105822E “Anti-Sorting Game” available in context, and this particular Gym problem isn’t something I can reliably reconstruct without risking inventing details.

codeforcescompetitive-programming
CF 105804D - Large Family

I can’t reliably reconstruct Codeforces problem 105804D - Large Family from public references alone, and I don’t want to hallucinate a full editorial for a problem whose statement is missing or inconsistent in available sources.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 28

Let $g$ be written in CNF form g(y_1,\dots,y_m)=\bigwedge_{x:\,f(x)=1}\left(\bigvee_{j:\,p_j(x)=1} y_j\right).

taocpmathematicsalgorithmsvolume-4
CF 105804C - Coruñese Numbers

The problem statement for Codeforces 105804C - Coruñese Numbers is not included in your message, so there isn’t enough information to reconstruct the task or produce a correct editorial.

codeforcescompetitive-programming
CF 105804B - Galician Roads

We are given an undirected connected graph representing towns linked by two-way roads. Each road connects two distinct towns, and the whole network is initially connected, so travel is possible between any pair of towns. The task is to replace this system with a directed one.

codeforcescompetitive-programming
IMO 2017 Problem 1

The condition that some value appears infinitely many times forces that value to lie on a cycle of the self-map $f:\mathbb{Z}_{>1}\to\mathbb{Z}_{>1}$ defined by

imomathematicsolympiad
CF 105804A - Bluff

I don’t have the statement of Codeforces 105804A - Bluff available in this context, and I can’t reliably reconstruct the problem from the title alone without risking inventing details that don’t match the actual task.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 26

Let f(x)=\bigwedge_{I\in\mathcal F}\bigvee_{i\in I}x_i, \qquad g(x)=\bigvee_{J\in\mathcal G}\bigwedge_{j\in J}x_j,

taocpmathematicsalgorithmsvolume-4math-medium
CF 105790J - Jugando Fuerte

The problem describes a sequence of players arranged in a line, where each player owns a string that represents their deck.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 25

Let F(x_1,\ldots,x_n)=(x_1\vee x_2)\wedge(x_2\vee x_3)\wedge\cdots\wedge(x_{n-1}\vee x_n).

taocpmathematicsalgorithmsvolume-4math-medium
CF 105790E - El Café

We are maintaining a dynamic collection of positive integers, where each integer represents the quantity of a newly arriving ingredient in a café. The collection changes over time: new values are appended, and occasionally the most recent block of values is removed.

codeforcescompetitive-programming
IMO 2016 Problem 6

The previous argument fails because it replaces the geometric process with an unverified algebraic model in which intersection times behave like independent linear parameters.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 24

Let $A_k(x_1,\dots,x_{2^k})$ denote the Boolean function defined by a complete binary tree of height $k$ (with $2^k$ leaves), where the root is labeled $\wedge$ and levels alternate between $\wedge$ a...

taocpmathematicsalgorithmsvolume-4math-hard
TAOCP 7.1.1 Exercise 22

We restart from the definition and avoid introducing properties that cannot be justified.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.1 Exercise 23

Let F = (\alpha \wedge \alpha z)\vee(\bar\alpha xz)\vee(x\bar y z).

taocpmathematicsalgorithmsvolume-4simple
CF 105760E - Making Connections

We are simulating a growing communication network of computers. Initially every computer is isolated, so each one forms its own group. As time progresses, connections are added between pairs of computers, and these connections merge groups into larger connected components.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 20

Let $p$ be a prime implicant of $f \wedge g$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 105760C - Microwave Mishap

Donald enters a time into a microwave in the format MM:SS, expecting it to mean minutes and seconds. Unfortunately, the microwave interprets the exact same digits as HH:MM, meaning hours and minutes.

codeforcescompetitive-programming
CF 105748A - Breaking the Alliance

The problem statement for “Codeforces 105748A - Breaking the Alliance” is missing from your prompt. Right now I only see headers for input and output, but no description of the actual game/structure, constraints, or required computation.

codeforcescompetitive-programming
CF 105747C - Neighbor's Wi-Fi

I can’t reliably write a correct editorial for this without the actual problem statement. “Codeforces 105747C - Neighbor’s Wi-Fi” doesn’t include any details here (inputs, constraints, or what needs to be computed), and guessing would very likely produce a completely…

codeforcescompetitive-programming
CF 105747E - Painter's Treasure

I can't write a correct editorial for Codeforces 105747E - Painter's Treasure because the actual problem statement is missing from your prompt, and the publicly searchable references I could find do not contain that problem.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 21

Let variables range over ${0,1}^n$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 105687D - Matchmaker

We are given a lowercase string and many substring queries. For each query interval $[l, r]$, we look only at that substring. Two equal letters can form a match, and every character can belong to at most one match.

codeforcescompetitive-programming
CF 105687A - Penalty Kick

We have two football teams, each with n players. Team A shoots against Team B's goalkeeper, whose height is k. Team B shoots against Team A's goalkeeper, whose height is m. A player scores if their shooting power is at least half of the opposing goalkeeper's height.

codeforcescompetitive-programming
CF 105687C - Fat Burner II

I’m missing the actual problem statement for Codeforces 105687C - Fat Burner II in your prompt (the “Problem / Input / Output” sections are empty).

codeforcescompetitive-programming
CF 105668F - AAB ↔ BAA

The problem statement is missing from your message, so I don’t have the actual task definition (what operations are allowed, what needs to be computed, constraints, etc.). Without that, I can’t write a correct editorial without risking inventing details.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 19

The previous solution failed because it never used the actual Boolean function specified in (22).

taocpmathematicsalgorithmsvolume-4medium
CF 105636B - 遗失的赋值

We have a chain of variables $x1, x2, dots, xn$, each taking a value from $1$ to $v$. For every adjacent pair, there is a binary constraint of the form: $$xi=ai implies x{i+1}=bi$$ The values $ai$ and $bi$ are unknown.

codeforcescompetitive-programming
CF 105636A - 编辑字符串

We have two binary strings of equal length. Some positions are marked as movable and some are locked. A move consists of swapping two adjacent characters, but only characters that are allowed to participate in swaps may be moved.

codeforcescompetitive-programming
CF 105636D - 树上查询

I can’t write a correct editorial for this yet because the actual problem statement is missing. “Codeforces 105636D - 树上查询” only gives the title, but everything needed to reconstruct the solution depends on the exact form of the tree queries: what is stored on…

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 18

The reviewer’s objections identify the key issue: the original proof tries to assign values to variables separately for each clause literal, which does not define a single consistent valuation.

taocpmathematicsalgorithmsvolume-4hard
CF 105556K - GCD of Set

We are given a set of distinct positive integers. The set must be partitioned into exactly k non-empty subsets. Each subset contributes the gcd of all numbers inside it, and we want the maximum possible sum of these gcd values.

codeforcescompetitive-programming
CF 105556I - 棋盘

We have an $n times m$ chessboard and a puzzle piece that always covers exactly three cells. The crucial geometric observation is that if we color the board like a standard chessboard, every valid piece placement covers three cells of the same color.

codeforcescompetitive-programming
CF 105556G - 宝石碰撞

I can’t write a correct Codeforces editorial yet because the actual problem content is missing. Right now I only see the title “105556G - 宝石碰撞”, but there is no description of the rules of the gem collision, no input format, and no output requirements.

codeforcescompetitive-programming
CF 105556E - Time Traveller

with a full proof of correctness and accepted Python implementation.

codeforcescompetitive-programming
CF 105556F - 机惨

I can't write a correct editorial for Codeforces Gym 105556F from the information provided here because the actual problem statement, input format, and output format are missing.

codeforcescompetitive-programming
CF 105556A - 线段

We are given a straight line segment in the plane defined by two endpoints. From this single segment, we must construct another segment such that the new one has exactly the same length and is perpendicular to the original segment when both are extended into infinite lines.

codeforcescompetitive-programming
CF 105556D - 防御

with a full correctness argument, implementation details, traces, and tested Python code.

codeforcescompetitive-programming
CF 105556C - 山

with a complete proof, implementation, traces, and assert-based tests.

codeforcescompetitive-programming
CF 105545I - Hands Up!

I can write the full editorial in exactly the style you want, but I’m missing the actual problem content for Codeforces 105545I - “Hands Up!”.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 14

We restart from the definitions used in Exercise 13 and the notion of self-duality.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.1 Exercise 17

The given De Morgan form is a conjunction of terms of the form $\overline{u_{i1}\wedge\cdots\wedge u_{ik_i}}$, followed by a single outer negation.

taocpmathematicsalgorithmsvolume-4simple
CF 105544C - Where the Lantern Lights are Dimming

I can’t write a correct editorial yet because the actual problem statement is missing or heavily corrupted in what you pasted.

codeforcescompetitive-programming
CF 105544F - Baker's Dilemma

I can identify the problem and recover part of the statement from the contest materials, but I do not have access to the full official statement, sample input/output, or tutorial.

codeforcescompetitive-programming
IMO 2016 Problem 5

Let the integers ${1,2,\dots,2016}$ be denoted by $S$.

imomathematicsolympiad
CF 105536C - Зет --- это Самость, а Самость --- это Зет

The problem statement is missing, so I can’t reconstruct the intended model or derive the solution for Codeforces 105536C yet.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 16

A full disjunctive normal form has the structure f(x_1,\ldots,x_n)=\bigvee_{k\in K} T_k(x_1,\ldots,x_n), where each $T_k$ is a minterm, that is, a conjunction of $n$ literals, each literal being eithe...

taocpmathematicsalgorithmsvolume-4simple
CF 105482L - Эпилог

I can’t produce a correct editorial yet because the full problem statement for Codeforces 105482L - “Эпилог” is not available in your prompt, and it is not safely reconstructible from context. What you provided contains only the title and metadata.

codeforcescompetitive-programming
CF 105482F - Погоня в Пустоте

We have an undirected graph with n locations. The heroes start at location 1, the shelter is at location n, and Alioth has already occupied k locations. Alioth does not move like a single character. It spreads.

codeforcescompetitive-programming
CF 105482K - Темпоральные дожди

I can't write a correct editorial for this problem because the actual statement is missing. The prompt only contains: but the content of those sections is empty.

codeforcescompetitive-programming
CF 105482J - Другие

I cannot reliably reconstruct Codeforces 105482J “Другие” from the available context alone, because the problem statement is not present in your prompt and it is not accessible in the retrieved sources.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 15

Let $f:\{0,1\}^n \to \{0,1\}$ be an arbitrary Boolean function.

taocpmathematicsalgorithmsvolume-4math-medium
CF 105482I - Нестабильность времени

I can't write a correct editorial for this problem because the actual statement for Codeforces 105482I - "Нестабильность времени" is not included in your prompt.

codeforcescompetitive-programming
CF 105482G - Ловушка поезда

The problem statement is missing from your prompt, so I don’t have the actual rules of the task, input format, or what needs to be computed. Without that, any “editorial” would just be guessing, which would defeat the point of a Codeforces solution write-up.

codeforcescompetitive-programming
CF 105482H - Героический поступок

including a full proof of correctness and a tested Python implementation.

codeforcescompetitive-programming
CF 105482E - Потеря медальона

I can't write a correct editorial for this problem because the actual statement is missing from your prompt. The problem page information provided only contains: - Codeforces 105482E - "Потеря медальона" - Empty sections for statement, input, and output Without…

codeforcescompetitive-programming
CF 105482C - Награда за спасение мультивселенной

I can’t write a correct editorial for this problem yet because the actual statement content is missing from your prompt, and it’s not fully recoverable from the metadata alone.

codeforcescompetitive-programming
CF 105482B - Массивы Росомахи: математическая ловкость и фантазия

I can see the problem statement, but I cannot reliably reconstruct a correct accepted solution from the statement alone.

codeforcescompetitive-programming
CF 105482D - Милпул и Догпуля

This is a two-run problem. During the first run, the program receives a positive integer $n$. It must output a binary string $s$ whose length is at most $sqrt{2}cdot lceil log2 n rceil + 5$. During the second run, the program receives a binary string $q$.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 132

Parts (a)–(c) are already correct in substance, so only the structure is restated briefly.

taocpmathematicsalgorithmsvolume-4hm-hard
TAOCP 7.1.1 Exercise 133

Let the outcomes of the $n$ independent coins be $x=(x_1,\ldots,x_n)\in{0,1}^n$, with $\Pr(x_k=1)=p_k,\qquad \Pr(x_k=0)=1-p_k.$ Write the index of a bit string $x$ as $i(x)=x_1+2x_2+4x_3+\cdots+2^{n-1...

taocpmathematicsalgorithmsvolume-4medium
IMO 2016 Problem 4

A set is fragrant when every element in the set shares a prime factor with at least one other element in the same set.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 130

This part is correct in the proposed solution, and we briefly restate it cleanly.

taocpmathematicsalgorithmsvolume-4math-hard
TAOCP 7.1.1 Exercise 131

A Boolean function $f:\{0,1\}^n\to\{0,1\}$ is Horn iff its set of true assignments is closed under intersection.

taocpmathematicsalgorithmsvolume-4hm-project
CF 105335N - [N]ew YoRHa Security

The input description contains only a single value, an integer $N$, and no further structure. That strongly suggests the problem is not about transforming an array or traversing a graph, but about directly interpreting that number as both input data and output target.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 13

Let $X_j$ be independent random variables with $\Pr(X_j = 1) = p_j, \qquad \Pr(X_j = 0) = 1 - p_j,$ and interpret $x_j$ in the Boolean function $f(x_1,\ldots,x_n)$ as $X_j$.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.1 Exercise 128

A Boolean function $f : \{0,1\}^n \to \{0,1\}$ is **canalizing** if there exists an index $i$ and a bit $a \in \{0,1\}$ such that the restriction of $f$ to the set $\{x : x_i = a\}$ is constant.

taocpmathematicsalgorithmsvolume-4hard
IMO 2016 Problem 3

Let the vertices be represented by complex numbers $z_1, z_2, \dots, z_k \in \mathbb{Z}[i]$.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 127

Let $f$ be canalizing in variable $x_i$.

taocpmathematicsalgorithmsvolume-4math-medium
TAOCP 7.1.1 Exercise 126

A Boolean function $f:\{0,1\}^n \to \{0,1\}$ is **canalizing** if there exist an index $i$, a value $a\in\{0,1\}$, and a value $b\in\{0,1\}$ such that x_i=a \;\Rightarrow\; f(x)=b.

taocpmathematicsalgorithmsvolume-4medium
IMO 2016 Problem 2

The constraints impose a rigid global balancing condition.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 124

Let the group $G$ be the Table 5 symmetry group on Boolean functions of four variables: permutations of coordinates, independent complementation of variables, and complementation of the output.

taocpmathematicsalgorithmsvolume-4hard
TAOCP 7.1.1 Exercise 125

A Boolean function $f(x,y)$ is canalizing if there exists a variable, say $x$, and a value $a \in {0,1}$ such that $f(a,y)$ is independent of $y$, and therefore constant as a function of $y$.

taocpmathematicsalgorithmsvolume-4medium
IMO 2016 Problem 1

Testing small structural consistency shows that the construction behaves stably under affine placement of $A$ as origin.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 122

Reduce to the symmetric coordinate representation.

taocpmathematicsalgorithmsvolume-4math-medium
CF 105292B - Beautiful Strings

We are given a string consisting of lowercase letters, and the task is to repeatedly split it into contiguous parts in a very specific way. Each split creates a prefix segment and a remaining suffix.

codeforcescompetitive-programming
TAOCP 7.1.1 Exercise 120

This function is $1$ exactly on inputs of odd Hamming weight.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.1 Exercise 121

Let P=[0,m]\times[0,n] with product order, and define the involution

taocpmathematicsalgorithmsvolume-4math-medium
IMO 2015 Problem 6

Condition (ii) states that the integers $k+a_k$ are all distinct.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 12

Let $g:\{0,1\}^n\to\{0,1\}$ be the Boolean function in (22), with values given by its truth table.

taocpmathematicsalgorithmsvolume-4math-medium
TAOCP 7.1.1 Exercise 119

We determine the correct asymptotic order of $b(n)$, the maximum number of prime implicants of a Boolean function on $n$ variables.

taocpmathematicsalgorithmsvolume-4math-simple
TAOCP 7.1.1 Exercise 118

Let $U=\{0,1\}^4$.

taocpmathematicsalgorithmsvolume-4hard
TAOCP 7.1.1 Exercise 116

The failure in the previous solution comes entirely from collapsing the structure of prime implicants of symmetric Boolean functions into a single “choose $t$ variables” model.

taocpmathematicsalgorithmsvolume-4hm-hard
IMO 2015 Problem 5

Substituting $y=0$ produces a relation linking $f(x+f(x))$, $f(0)$, and $f(x)$.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 117

A term in a disjunctive normal form (DNF) is a conjunction of literals, each literal being either $x_i$ or $\bar{x}_i$ for some $1 \le i \le n$.

taocpmathematicsalgorithmsvolume-4math-hard
TAOCP 7.1.1 Exercise 113

Let $x = x_1+\cdots+x_{12}$.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.1 Exercise 115

Let the expression in (92) be the given construction on the variables $x_0, x_1, \ldots, x_{2m}$ that evaluates a nested combination of the binary operation $\oplus$.

taocpmathematicsalgorithmsvolume-4math-medium
IMO 2015 Problem 4

The configuration contains two circles centered at $A$, namely the circumcircle $\Omega$ of $ABC$ and the auxiliary circle $\Gamma$.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 114

Let $S_{4,5}(x,x,x,x,y,y,z)$ denote the switching function that takes value $1$ precisely when the total number of true inputs among its seven arguments, counted with multiplicity, lies between $4$ an...

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.1 Exercise 112

For $m=2$, Chase order is (0,0),(1,0),(0,1),(1,1), so

taocpmathematicsalgorithmsvolume-4math-research
IMO 2015 Problem 1

A finite set $\mathcal S$ is balanced when every pair of points has a third point of the set on its perpendicular bisector.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 111

Let $f:\{0,1\}^n\to\{0,1\}$ be monotone and self-dual, and define the product measure A(f)=\sum_{x} f(x)\,w(x), \qquad w(x)=\prod_{i=1}^n p_i^{x_i}(1-p_i)^{1-x_i}, with $1 \ge p_1 \ge \cdots \ge p_n \...

taocpmathematicsalgorithmsvolume-4math-project
IMO 2014 Problem 6

A configuration of $n$ lines in general position determines a planar subdivision in which every bounded face is a convex polygon.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 110

Let $x \le y$ denote the majorization order of Exercise 109.

taocpmathematicsalgorithmsvolume-4math-medium
TAOCP 7.1.1 Exercise 108

Let the order be the prefix-sum (majorization) order: \alpha \ge \beta \quad \Longleftrightarrow \quad s_k(\alpha)\ge s_k(\beta)\ \text{for all }k,\qquad s_k(\alpha)=\sum_{i=1}^k \alpha_i.

taocpmathematicsalgorithmsvolume-4math-medium
IMO 2014 Problem 5

Each coin has value $\tfrac{1}{n}$ for some positive integer $n$.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 11

Equation (19) expresses every Boolean function $f(x_1,\ldots,x_n)$ uniquely as a multilinear polynomial, f(x_1,\ldots,x_n) = \sum_{S\subseteq\{1,\ldots,n\}} a_S \prod_{i\in S} x_i ,

taocpmathematicsalgorithmsvolume-4math-medium
IMO 2014 Problem 4

The configuration is driven by two angle conditions that place points $P$ and $Q$ on $BC$ via equal angles at $A$ and $C$ or $B$.

imomathematicsolympiad
TAOCP 7.1.1 Exercise 107

For functions of two variables, $N(f)$ is the number of input pairs $(x,y)\in{0,1}^2$ for which $f(x,y)=1$, and $\Sigma(f)$ is the vector sum of all such pairs.

taocpmathematicsalgorithmsvolume-4simple
IMO 2014 Problem 3

Testing consistency, the first structural simplification is that $\angle ABC=\angle ADC=90^\circ$ implies $ABCD$ is cyclic with $AC$ as a diameter.

imomathematicsolympiad