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43815 notes

CF 290A - Mysterious strings

The entire task is a joke problem from the April Fools contest. The input is a single integer a between 1 and 40. Instead of computing anything, we must output a specific string associated with that position.

codeforcescompetitive-programming*specialimplementation
CF 290C - WTF?

The input is not a conventional mathematical specification. Instead, it is a small program written in LOLCODE. The task is to determine what that program computes and print the resulting real number. The first input value is read into a variable that controls a loop.

codeforcescompetitive-programming*specialgraph-matchingsimplementationtrees
Kvant Math Problem 1446

Let $P$ be a convex polyhedron in $\mathbb{R}^3$ with vertices $V(P)={A,V_1,\dots,V_8}$.

kvantmathematicsolympiad
Kvant Math Problem 1447

No mathematical exploration is possible because the statement of Kvant problem M1447 is not provided.

kvantmathematicsolympiad
Kvant Math Problem 1445

Let a natural number $N$ satisfy the condition that after deleting one digit that is not the first digit, the resulting number $M$ divides $N$ with an integer quotient.

kvantmathematicsolympiad
Kvant Math Problem 1444

Consider polynomials with a negative coefficient, such as $P(x) = -x + 2$ or $P(x) = x^2 - x + 1$.

kvantmathematicsolympiad
Kvant Math Problem 1443

The problem statement for Kvant M1443 is not included, and the graphical version is not available here.

kvantmathematicsolympiad
Kvant Math Problem 1442

Solution to Kvant math problem 1442.

kvantmathematicsolympiad
Kvant Math Problem 1441

The textual statement of Kvant problem M1441 is not included, and the graphical version is referenced but not provided here.

kvantmathematicsolympiad
Kvant Math Problem 1440

I can write the solution as requested, but I need the full text of Kvant problem M1440 in order to proceed.

kvantmathematicsolympiad
Kvant Math Problem 1439

Before I can begin the full solution in your requested six-section format, I need the precise text of Kvant problem M1439.

kvantmathematicsolympiad
Kvant Math Problem 1438

The textual statement of Kvant M1438 is not included, and the graphical version is not accessible here.

kvantmathematicsolympiad
Kvant Math Problem 1437

The problem statement is not provided in textual or graphical form.

kvantmathematicsolympiad
Kvant Math Problem 1436

The statement of Kvant problem M1436 is not included, and the note indicates only a graphical version exists in the issue.

kvantmathematicsolympiad
Kvant Math Problem 1435

Before writing the full solution, I need the exact textual statement of Kvant Problem M1435.

kvantmathematicsolympiad
Kvant Math Problem 1434

Consider a simple convex polyhedron, such as a cube or a tetrahedron, and imagine casting a shadow onto a plane with a point light source.

kvantmathematicsolympiad
Kvant Math Problem 1433

I can do this, but I need the **textual statement of Kvant problem M1433** to proceed.

kvantmathematicsolympiad
Kvant Math Problem 1432

Consider a sequence of positive numbers $a_1, a_2, \dots$.

kvantmathematicsolympiad
Kvant Math Problem 1431

Let the operation be $f(10k+d)=k+4d$ with $0\le d\le 9$.

kvantmathematicsolympiad
Kvant Math Problem 1430

The sequence ${a_n}$ is monotonic and integer-valued.

kvantmathematicsolympiad
Kvant Math Problem 1429

I see that you want a full Kvant-style solution in six sections, but the actual textual statement of problem M1429 is missing.

kvantmathematicsolympiad
Kvant Math Problem 1428

Before I start, I need the full text of Kvant problem M1428.

kvantmathematicsolympiad
Kvant Math Problem 1427

I notice that the textual statement of Kvant problem M1427 has not been provided.

kvantmathematicsolympiad
Kvant Math Problem 1426

Consider the function $f(n) = n + S(n)$, where $S(n)$ is the sum of the digits of $n$.

kvantmathematicsolympiad
Kvant Math Problem 1425

Consider a quadrilateral with three interior angles of $45^\circ$.

kvantmathematicsolympiad
Kvant Math Problem 1424

For a sequence $a_1,\dots,a_n$, the transformation replaces each entry by the number of strictly larger elements to its right.

kvantmathematicsolympiad
Kvant Math Problem 1423

Consider three players $A$, $B$, and $C$, each playing the same number of games against one another.

kvantmathematicsolympiad
Kvant Math Problem 1422

Before proceeding, I need the full textual statement of Kvant M1422.

kvantmathematicsolympiad
Kvant Math Problem 1421

I cannot write a solution to Kvant M1421 because the problem statement itself is not present in your message.

kvantmathematicsolympiad
Kvant Math Problem 1420

Before I begin writing the solution, I need the text of Kvant problem M1420.

kvantmathematicsolympiad
Kvant Math Problem 1419

I cannot write a solution to Kvant problem M1419 because the actual problem statement is not present in your message.

kvantmathematicsolympiad
Kvant Math Problem 1418

I cannot write a solution to Kvant problem M1418 because the problem statement itself is not present in the conversation.

kvantmathematicsolympiad
Kvant Math Problem 1417

I see that the problem statement for Kvant M1417 is not yet fully provided in text form.

kvantmathematicsolympiad
Kvant Math Problem 1416

Consider a small finite set of gangsters.

kvantmathematicsolympiad
Kvant Math Problem 1415

Consider two regular decagons, each with 10 vertices, and numbers $a_1,\dots,a_{10}$ on the first decagon and $b_1,\dots,b_{10}$ on the second, all natural numbers, summing to 99 on each decagon.

kvantmathematicsolympiad
Kvant Math Problem 1414

I do not yet have the full text of Kvant problem M1414.

kvantmathematicsolympiad
Kvant Math Problem 1413

Let $N$ be the number of inhabitants, $T$ the number of truth-tellers, and $L=N-T$ the number of liars.

kvantmathematicsolympiad
Kvant Math Problem 1412

I cannot write a rigorous solution to Kvant problem M1412 because the actual problem statement is missing.

kvantmathematicsolympiad
Kvant Math Problem 1411

I can follow your requested format, but I need the full textual statement of Kvant problem M1411 to produce the solution.

kvantmathematicsolympiad
Kvant Math Problem 1410

Consider first the two-dimensional question.

kvantmathematicsolympiad
Kvant Math Problem 1409

Consider the equilateral triangle of side $n$ subdivided into $n^2$ unit equilateral triangles.

kvantmathematicsolympiad
Kvant Math Problem 1408

Consider small circles of people and the statements they can make.

kvantmathematicsolympiad
Kvant Math Problem 1407

Consider a small example with two central men.

kvantmathematicsolympiad
Kvant Math Problem 1406

Consider small examples.

kvantmathematicsolympiad
Kvant Math Problem 1405

Consider a small example, such as a pyramid with a square base.

kvantmathematicsolympiad
Kvant Math Problem 1404

We are asked to maximize the expression

kvantmathematicsolympiad
Kvant Math Problem 1403

Consider a convex $n$-gon $A_1A_2\ldots A_n$ and construct points $B_k$ on each side $A_kA_{k+1}$ such that $A_{k+1}B_k = A_kA_{k+1}$.

kvantmathematicsolympiad
Kvant Math Problem 1402

Consider the inequality for small values of $n$ to understand its behavior.

kvantmathematicsolympiad
Kvant Math Problem 1401

Consider triangle $ABC$ with circumcircle $\Gamma$ and a point $K$ chosen on the arc $BC$ that does not contain $A$.

kvantmathematicsolympiad
Kvant Math Problem 1400

A shortest closed route that visits all four faces can be replaced by a polygonal route whose vertices lie on the faces.

kvantmathematicsolympiad
Kvant Math Problem 1399

I cannot write a rigorous solution to Kvant problem M1399 because the actual problem statement is not present in your message.

kvantmathematicsolympiad
CF 290F - Greedy Petya

We are given an undirected graph with up to 20 vertices and up to 400 edges, and we need to decide whether there exists a simple path that visits every vertex exactly once.

codeforcescompetitive-programming*specialdfs-and-similargraphsgreedy
CF 290E - HQ

We are given a single string made from a very small alphabet inspired by the HQ family of joke languages. The task is to decide whether this string is “valid” under the rules of the language HQ, and output either confirmation or rejection.

codeforcescompetitive-programming*specialconstructive-algorithms
CF 290D - Orange

We are given a string consisting of English letters, both uppercase and lowercase, and an integer representing a "capitalization budget" between 0 and 26.

codeforcescompetitive-programming*specialimplementation
CF 290B - QR code

The problem gives two small integers, each between 0 and 32 inclusive. You can think of them as describing how many unit squares are placed along two perpendicular directions of a grid-like construction.

codeforcescompetitive-programming*specialimplementation
CF 289B - Polo the Penguin and Matrix

We are given a rectangular grid of integers, and we are allowed to perform a very specific operation: pick a single cell and add or subtract a fixed value d to it. Each such operation costs one move.

codeforcescompetitive-programmingbrute-forcedpimplementationsortingsternary-search
Kvant Math Problem 1398

The statement of Kvant problem M1398 is not included in your message.

kvantmathematicsolympiad
CF 289A - Polo the Penguin and Segments

We are given several integer intervals on the number line. Each interval represents a continuous block of covered integers, and the segments do not overlap or touch in any way.

codeforcescompetitive-programmingbrute-forceimplementation
CF 288B - Polo the Penguin and Houses

We are asked to count how many ways we can assign integers to the plaques of n houses in Polo’s village such that three conditions hold. Each house i has a plaque value p₁…pₙ, and Polo can follow the plaques as a chain from one house to the next.

codeforcescompetitive-programmingcombinatorics
Kvant Math Problem 1397

Consider first a simple convex polyhedron, such as a tetrahedron.

kvantmathematicsolympiad
CF 288C - Polo the Penguin and XOR operation

We are asked to consider permutations of all integers from 0 to n, inclusive. Polo defines the beauty of a permutation as the sum of XORs of consecutive elements.

codeforcescompetitive-programmingimplementationmath
CF 288E - Polo the Penguin and Lucky Numbers

We are given two extremely large integers, both written using only the digits 4 and 7. They have the same number of digits, and we are guaranteed that the first is strictly smaller than the second.

codeforcescompetitive-programmingdpimplementationmath
Kvant Math Problem 1396

I do not have the full text of Kvant problem M1396, so I cannot write a complete, rigorous solution yet.

kvantmathematicsolympiad
CF 288D - Polo the Penguin and Trees

We are given a tree with n nodes, each node numbered from 1 to n, and n-1 edges connecting them. Polo wants to count pairs of node-to-node paths that do not share any nodes.

codeforcescompetitive-programmingcombinatoricsdfs-and-similartrees
Kvant Math Problem 1395

Consider a small social network where each person has a certain number of acquaintances.

kvantmathematicsolympiad
CF 288A - Polo the Penguin and Strings

We are asked to construct a string of length n that contains exactly k distinct lowercase letters, where no two consecutive letters are the same, and the string is lexicographically smallest among all possibilities.

codeforcescompetitive-programminggreedy
CF 286B - Shifting

We are asked to generate a permutation of numbers from 1 to n that becomes "beautiful" after a sequence of block-cyclic shifts. The transformation takes a permutation and an integer k and splits the permutation into consecutive blocks of length k.

codeforcescompetitive-programmingimplementation
CF 286C - Main Sequence

We are given an encrypted version of a “correct bracket sequence” using integers instead of traditional parentheses. Each integer represents a bracket type, and its sign indicates whether it is an opening or closing bracket.

codeforcescompetitive-programminggreedyimplementation
Kvant Math Problem 1394

I see that you have provided the full template and instructions for solving Kvant problem M1394, but the actual problem statement has not been included yet.

kvantmathematicsolympiad
CF 286E - Ladies' Shop

We are given a set of bags, each with a minimum weight capacity. We need to define a minimal set of item weights such that any total weight that a bag can hold can be formed using these items in unlimited quantities.

codeforcescompetitive-programmingconstructive-algorithmsfftmath
CF 286D - Tourists

We are given a sequence of moments when pairs of tourists start walking, and another sequence of “walls” that appear over time.

codeforcescompetitive-programmingdata-structuressortings
CF 286A - Lucky Permutation

We are asked to construct a permutation of numbers from 1 to n such that applying the permutation twice maps an element at position i to the mirrored position n - i + 1. Formally, if p is the permutation, then for every i between 1 and n, we must have p[p[i]] = n - i + 1.

codeforcescompetitive-programmingconstructive-algorithmsmath
Kvant Math Problem 1393

I cannot write a solution to Kvant problem M1393 because the actual problem statement is not present in your message.

kvantmathematicsolympiad
CF 285C - Building Permutation

We are given an array of integers and we are allowed to modify it using unit increments or decrements. Each such operation costs one move. The goal is to transform the array into a permutation of size n, meaning we must end up with exactly the numbers from 1 to n, each used once.

codeforcescompetitive-programminggreedyimplementationsortings
CF 285B - Find Marble

We have a row of n glasses, each uniquely indexed from 1 to n. A marble starts under the glass at position s. Petya defines a permutation of the positions that determines how glasses are moved simultaneously during a shuffle.

codeforcescompetitive-programmingimplementation
Kvant Math Problem 1392

The quadrilateral $ABCD$ has three consecutive sides equal, $AB = BC = CD = 1$, and points $B$ and $C$ are fixed.

kvantmathematicsolympiad
CF 285E - Positions in Permutations

We are asked to count permutations of length n that have exactly k positions where the absolute difference between the value and its index is exactly 1. A permutation of length n is a sequence containing all integers from 1 to n in some order without repetition.

codeforcescompetitive-programmingcombinatoricsdpmath
CF 285D - Permutation Sum

We are asked to count pairs of permutations (a, b) of length n such that their modular sum produces another valid permutation c. For each index i, c[i] = ((a[i]-1 + b[i]-1) mod n) + 1. This is a bijective operation, meaning every element of c must be unique and within 1 to n.

codeforcescompetitive-programmingbitmaskscombinatoricsdpimplementationmeet-in-the-middle
CF 285A - Slightly Decreasing Permutations

We are asked to construct a permutation of numbers from 1 to n that has exactly k positions where a number is greater than the number immediately after it. In other words, we need a sequence of length n where precisely k "descents" occur.

codeforcescompetitive-programminggreedyimplementation
CF 283B - Cow Program

We are given a sequence of positive integers of length n where the first element is initially unknown and the remaining n - 1 elements are provided. The "cow program" defines two integer variables, x and y, starting with x = 1 and y = 0.

codeforcescompetitive-programmingdfs-and-similardpgraphs
Kvant Math Problem 1391

Solution to Kvant math problem 1391.

kvantmathematicsolympiad
CF 283A - Cows and Sequence

We start with a sequence containing a single element, 0, and perform a sequence of n operations. Operations can modify the sequence in three ways: increasing the first a elements by some value x, appending a new number to the end, or removing the last element.

codeforcescompetitive-programmingconstructive-algorithmsdata-structuresimplementation
CF 283E - Cow Tennis Tournament

Codeforces 283E: Cow Tennis Tournament

codeforcescompetitive-programmingcombinatoricsdata-structuresmath
Kvant Math Problem 1390

I can follow your requested format rigorously, but I need the **text of Kvant problem M1390** to proceed.

kvantmathematicsolympiad
Kvant Math Problem 1389

I cannot write a rigorous solution to Kvant problem M1389 because the actual problem statement is not present in your message.

kvantmathematicsolympiad
CF 283D - Cows and Cool Sequences

Codeforces 283D: Cows and Cool Sequences

codeforcescompetitive-programmingdpmathnumber-theory
CF 283C - Coin Troubles

We have n coin types. Coin type i has value a[i], and we may take any nonnegative number of coins of that type. The total value of all chosen coins must be exactly t. In addition, we are given inequality constraints of the form: count[b] count[c] The constraints are special.

codeforcescompetitive-programmingdp
CF 282A - Bit++

The problem presents a toy programming language with only one variable, x, initially set to zero. Each line of the program is a statement that either increments or decrements this variable.

codeforcescompetitive-programmingimplementation
Kvant Math Problem 1388

Let $f(x)=x^2+bx+c$ and $g(x)=x^2+px+q$, since both quadratics have leading coefficient $1$.

kvantmathematicsolympiad
CF 282B - Painting Eggs

We are asked to distribute a sequence of eggs between two children, A and G, where each egg has an individual cost for each child. The key constraints are that the total paid to A and the total paid to G must not differ by more than 500.

codeforcescompetitive-programminggreedymath
CF 282E - Sausage Maximization

We are given a single array of integers, which represents a sausage in Bitland. The goal is to cut this sausage into two non-overlapping segments: a prefix for BitHaval and a suffix for BitAryo. Either segment can be empty.

codeforcescompetitive-programmingbitmasksdata-structurestrees
CF 282D - Yet Another Number Game

We are asked to determine the winner in a turn-based game with a very small sequence of integers, where two players alternate moves. On each turn, a player can either reduce a single element by any positive amount or reduce all elements by the same positive amount.

codeforcescompetitive-programmingdpgames
Kvant Math Problem 1387

I cannot write a solution to Kvant M1387 because the problem statement itself is not included in your message.

kvantmathematicsolympiad
CF 282C - XOR and OR

We are given two binary strings. An operation chooses any adjacent pair of bits. If the pair is (x, y), we compute: - p = x xor y - q = x or y We then write p into one position and q into the other position, in either order. The length of the string never changes.

codeforcescompetitive-programmingconstructive-algorithmsimplementationmath
CF 281A - Word Capitalization

The task is to take a single word consisting of English letters and make sure its first character is uppercase. The rest of the letters must remain exactly as they are in the input. For example, given the input "apple", the output should be "Apple".

codeforcescompetitive-programmingimplementationstrings
Kvant Math Problem 1386

I do not have access to the graphical version of Kvant problem M1386, and the text of the problem is not included in your message.

kvantmathematicsolympiad
CF 281B - Nearest Fraction

We are asked to approximate a given fraction $x/y$ with another fraction $a/b$ where $b$ is at most $n$. The goal is to make $ Conceptually, we are trying to find the "closest" fraction with a bounded denominator to a given fraction.

codeforcescompetitive-programmingbrute-forceimplementationtwo-pointers
Kvant Math Problem 1385

I can do that.

kvantmathematicsolympiad
CF 280B - Maximum Xor Secondary

We are given an array of distinct positive integers, and our task is to find the largest possible "lucky number" obtainable from any contiguous subarray of length at least two. A "lucky number" is defined as the bitwise XOR of the largest and second largest element in a subarray.

codeforcescompetitive-programmingdata-structuresimplementationtwo-pointers
Kvant Math Problem 1384

I can follow your requested format precisely, but I need the full text of Kvant problem M1384 to produce the complete solution.

kvantmathematicsolympiad