*special | brain

Practice › Codeforces Solutions › April Fools Day Contest ›

CF 171A - Mysterious numbers - 1

CF 171A - Mysterious numbers - 1 Rating: 1200 Tags: *special, constructive algorithms Solve time: 1m 43s Verified: yes Solution Problem Understanding This problem comes from an April Fools contest where the statement intentionally hides the real task. We are given two non-negative integers. The required operation is: Reverse the decimal representation of the second number. Add the result to the first number. Output the sum. For example, if the...

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April Fools Day Contest

April Fools Day Contest Type: April Fools | Problems: 8 | Verified: 8/8 | Rating range: 1200-2000 | Time: 13m 15s Problem Name Rating Tags Solve Time Verified A Mysterious numbers - 1 1200 *special, constructive-algorithms 1m 43s ✓ B Star 1300 *special, combinatorics 2m 57s ✓ C A Piece of Cake 2000 *special, implementation 1m 30s ✓ D Broken checker 1300 *special, brute-force 1m 14s ✓ E MYSTERIOUS LANGUAGE...

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CF 171H - A polyline

CF 171H - A polyline Rating: 1700 Tags: *special, implementation Solve time: 1m 39s Verified: yes Solution Problem Understanding The input contains two numbers. The first number, a , determines the order of a recursively constructed polyline. The second number, b , is an index along that polyline. The picture in the statement is the key. It is the classical Hilbert curve, a space-filling curve that visits every cell of...

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CF 171G - Mysterious numbers - 2

CF 171G - Mysterious numbers - 2 Rating: 1600 Tags: *special Solve time: 2m Verified: yes Solution Problem Understanding We are given three small positive integers, a1, a2, and a3, each ranging from 1 to 20. The problem asks us to compute a single integer as output based on these three numbers. While the problem’s description is minimal, the underlying task is to enumerate all possible “mysterious numbers” that can...

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CF 171F - ucyhf

CF 171F - ucyhf Rating: 1600 Tags: *special, brute force, implementation, number theory Solve time: 1m 11s Verified: yes Solution Problem Understanding We are asked to find a special number associated with a single integer input d , where d represents a divisor or parameter in a number-theoretic sequence. The output is another integer computed from d according to a hidden mathematical rule, likely involving divisibility, modular arithmetic, or a...

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CF 171E - MYSTERIOUS LANGUAGE

CF 171E - MYSTERIOUS LANGUAGE Rating: 2000 Tags: *special Solve time: 1m 1s Verified: yes Solution Problem Understanding This is one of Codeforces' classic "special" problems. Unlike ordinary algorithmic tasks, there is no meaningful input to process and no data structure or optimization challenge to solve. The contest provides access to a language called Secret through the custom test environment. The actual challenge is to determine what programming language "Secret"...

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CF 171D - Broken checker

CF 171D - Broken checker Rating: 1300 Tags: *special, brute force Solve time: 1m 14s Verified: yes Solution Problem Understanding This is one of the most unusual problems on Codeforces. The input is supposed to contain a single integer between 1 and 5. There are only five official test cases. The output must be a single integer between 1 and 3. The crucial detail is that there is no actual...

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CF 1952I - Dark Matter

CF 1952I - Dark Matter Rating: - Tags: *special, bitmasks, geometry Solve time: 48s Verified: yes Solution Problem Understanding The input describes a single arithmetic-style expression consisting of integers combined with the + operator. The key difference from standard arithmetic is that + does not mean numeric addition. Instead, each operation combines two numbers by treating them as binary strings and stitching them together. Concretely, when we see an expression...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 10 ›

CF 1958I - Equal Trees

CF 1958I - Equal Trees Rating: 3100 Tags: *special, graphs, meet-in-the-middle Solve time: 1m 8s Verified: no Solution Problem Understanding We are given two rooted trees on the same labeled vertex set from 1 to n, both rooted at 1. Each tree is described by its parent array, so every node knows its immediate parent except the root. We are allowed to perform a single kind of structural operation: pick...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 10 ›

CF 1958A - 1-3-5

CF 1958A - 1-3-5 Rating: 1100 Tags: *special, dp Solve time: 47s Verified: yes Solution Problem Understanding We are asked to construct an exact sum using coins of values 1, 3, and 5. For each target amount n, we want to pay exactly n using any number of 3 and 5 coins, and we are only forced to use 1-coins when it becomes unavoidable. The task is to minimize how...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 10 ›

CF 1958J - Necromancer

CF 1958J - Necromancer Rating: 3200 Tags: *special Solve time: 1m 12s Verified: yes Solution Problem Understanding We are simulating a very specific combat process on a fixed line of monsters, and answering many independent queries on subsegments of that line. Each query picks a segment $[l, r]$ and then runs a deterministic procedure that always attacks the leftmost remaining monster, repeatedly until it dies, and then permanently converts it...

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CF 1952B - Is it stated?

CF 1952B - Is it stated? Rating: - Tags: *special, strings Solve time: 41s Verified: yes Solution Problem Understanding We are given a list of strings, each consisting of lowercase English letters, and for each string, we are asked to answer either "YES" or "NO" based on a hidden pattern. Observing the sample inputs and outputs, the strings "it", "submit", and "timelimitexceeded" yield "YES", while others like "is", "stated", or...

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Kotlin Heroes: Episode 10

Kotlin Heroes: Episode 10 Type: Kotlin | Problems: 10 | Verified: 7/10 | Rating range: 1100-3200 | Time: 11m 13s Problem Name Rating Tags Solve Time Verified A 1-3-5 1100 *special, dp 47s ✓ B Clock in the Pool 1400 *special, math 44s ✓ C Firewood 1500 *special 1m ✓ D Staircase 1600 *special 1m 14s ✗ E Yet Another Permutation Constructive 1900 *special, constructive-algorithms 1m 4s ✗ F Narrow...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 10 ›

CF 1958H - Composite Spells

CF 1958H - Composite Spells Rating: 2600 Tags: *special, dp Solve time: 1m 34s Verified: yes Solution Problem Understanding We are given a spell system that behaves like a program written in a very restricted language. The first part of the system is a list of basic operations, each of which either increases or decreases a monster’s health by a fixed integer. After that comes a sequence of composite operations,...

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CF 1952F - Grid

CF 1952F - Grid Rating: - Tags: *special, brute force Solve time: 1m 12s Verified: no Solution Problem Understanding We are given a fixed-size grid of 21 rows and 21 columns. Each cell contains either 0 or 1 . The grid should be viewed as a map where each cell is a square tile, and tiles with the same value may form connected regions through shared edges. The task is...

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CF 1952A - Are You a Robot, Again?

CF 1952A - Are You a Robot, Again? Rating: - Tags: *special, strings Solve time: 32s Verified: yes Solution Problem Understanding In this problem, we are given a string of digits that a robot has produced. The robot operates under a simple but peculiar rule: for each digit in the string, if the digit is even, it will remain in the output string as-is. If the digit is odd, the...

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CF 1958F - Narrow Paths

CF 1958F - Narrow Paths Rating: 2000 Tags: *special, combinatorics Solve time: 1m 12s Verified: yes Solution Problem Understanding We are working on a very constrained grid: only two rows and a large number of columns. The start is the top-left cell, and the goal is the bottom-right cell. Movement is restricted to only right or down, which means any valid path must either stay on the top row for...

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2023 Post World Finals Online ICPC Challenge powered by Huawei

2023 Post World Finals Online ICPC Challenge powered by Huawei Type: ICPC/IOI | Problems: 1 | Verified: 1/1 | Rating range: - | Time: 52s Problem Name Rating Tags Solve Time Verified A Accuracy-Preserving Summation Algorithm - *special 52s ✓

Practice › Codeforces Solutions › April Fools Day Contest 2024 ›

CF 1952H - Palindrome

CF 1952H - Palindrome Rating: - Tags: *special, implementation, strings Solve time: 1m 12s Verified: no Solution Problem Understanding The task is to determine, for each given string, whether it reads the same forwards and backwards. A palindrome is such a string, like "radar" or "racecar", while a string like "ac" is not. The input consists of multiple test cases, each providing a string of up to 100 lowercase English...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 10 ›

CF 1958B - Clock in the Pool

CF 1958B - Clock in the Pool Rating: 1400 Tags: *special, math Solve time: 44s Verified: yes Solution Problem Understanding The clock is not a normal continuous display, it behaves like a repeating cycle of three states. Every cycle has length $3k$ seconds. At the beginning of each cycle, the clock shows water temperature, then after $k$ seconds it switches to air temperature, and after another $k$ seconds it switches...

Practice › Codeforces Solutions › 2023 Post World Finals Online ICPC Challenge powered by Huawei ›

CF 1953A - Accuracy-Preserving Summation Algorithm

CF 1953A - Accuracy-Preserving Summation Algorithm Rating: - Tags: *special Solve time: 52s Verified: yes Solution Problem Understanding We are given a long sequence of floating-point numbers, and we are asked to output a description of how to compute their total sum. The twist is that we are not directly computing the sum as a normal program output; instead, we are describing a computation plan that will later be executed...

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April Fools Day Contest 2024

April Fools Day Contest 2024 Type: April Fools | Problems: 8 | Verified: 5/8 | Rating range: - | Time: 7m 9s Problem Name Rating Tags Solve Time Verified A Are You a Robot, Again? - *special, strings 32s ✓ B Is it stated? - *special, strings 41s ✓ C They Have Fooled - *special, brute-force, schedules 52s ✓ F Grid - *special, brute-force 1m 12s ✗ G Mathematician Takeover...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 10 ›

CF 1958C - Firewood

CF 1958C - Firewood Rating: 1500 Tags: *special Solve time: 1m Verified: yes Solution Problem Understanding Monocarp has a single log of wood that weighs exactly $2^n$ grams. He needs to split this log into pieces such that he can assemble exactly $k$ grams of wood for today's fireplace, leaving the remaining $2^n-k$ grams for tomorrow. Each minute, Monocarp can split a log of weight $x > 1$ into two...

Practice › Codeforces Solutions › April Fools Day Contest 2024 ›

CF 1952C - They Have Fooled

CF 1952C - They Have Fooled Rating: - Tags: *special, brute force, schedules Solve time: 52s Verified: yes Solution Problem Understanding The input to this problem is a single integer $n$, with $0 \le n \le 12$. Despite how small this looks, the task is not about iterating or simulating anything directly from this number in a naive arithmetic sense. Instead, the problem asks for a fixed value that depends...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 10 ›

CF 1958E - Yet Another Permutation Constructive

CF 1958E - Yet Another Permutation Constructive Rating: 1900 Tags: *special, constructive algorithms Solve time: 1m 4s Verified: no Solution Problem Understanding We are given a permutation, which is just an ordering of the numbers from 1 to n. We repeatedly apply a transformation that removes elements which are strictly smaller than at least one of their immediate neighbors. After each round, the remaining elements form a shorter sequence, and...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 10 ›

CF 1958G - Observation Towers

CF 1958G - Observation Towers Rating: 2400 Tags: *special Solve time: 1m 18s Verified: yes Solution Problem Understanding Each observation tower sits at a fixed position on a number line from 1 to n and has a current viewing radius given by its height. A tower can “see” every integer point whose distance from its position does not exceed its height. Increasing the height expands this symmetric visibility interval, and...

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CF 1952G - Mathematician Takeover

CF 1952G - Mathematician Takeover Rating: - Tags: *special, binary search, dfs and similar, math Solve time: 1m 8s Verified: no Solution Problem Understanding We are given a single real number $x$ between 1 and 100, expressed to exactly three decimal places. The task is to compute a real number result from $x$, with the requirement that the answer's absolute or relative error does not exceed $10^{-4}$. The problem does...

Practice › Codeforces Solutions › Kotlin Heroes: Episode 10 ›

CF 1958D - Staircase

CF 1958D - Staircase Rating: 1600 Tags: *special Solve time: 1m 14s Verified: no Solution Problem Understanding We are given a line of staircase steps, each step either needing repair or already fine. If a step is fine, it behaves like a zero in the input. If it is broken, it carries a positive cost value that represents its repair difficulty. The repair process is constrained by days. Each day...

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Surprise Language Round 7

Surprise Language Round 7 Type: Special | Problems: 8 | Verified: 8/8 | Rating range: 1400-2300 | Time: 10m 9s Problem Name Rating Tags Solve Time Verified A Crystal Ball Sequence 1400 *special, implementation 1m 36s ✓ B Hexakosioihexekontahexaphobia 1800 *special 1m 6s ✓ C Eval 1900 *special 1m 2s ✓ D Caesar Cipher 1900 *special 1m 24s ✓ E Chessboard 1900 *special 1m 29s ✓ F Pairwise Sums 2300...

Practice › Codeforces Solutions › Surprise Language Round 7 ›

CF 470F - Pairwise Sums

CF 470F - Pairwise Sums Rating: 2300 Tags: *special Solve time: 1m 17s Verified: yes Solution Problem Understanding The problem asks us to take a list of integers and, for each element, produce the sum of that element with the element immediately preceding it. The twist is that the first element of the output pairs with the last element of the array, creating a circular relationship. Conceptually, you can think...

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CF 470G - Hamming Distance

CF 470G - Hamming Distance Rating: 2300 Tags: *special Solve time: 57s Verified: yes Solution Problem Understanding The task is to compute the Hamming distance between two strings of equal length. In practical terms, you are comparing two sequences of letters and counting how many positions contain different characters. Each mismatch contributes exactly one to the distance. For example, comparing CODECHEF and TOPCODER , every position where the letters differ...

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CF 470C - Eval

CF 470C - Eval Rating: 1900 Tags: *special Solve time: 1m 2s Verified: yes Solution Problem Understanding The task is to evaluate a simple arithmetic expression of the form a?b where a and b are integers between 1 and 999, and ? is a single operator from the set + , - , * , / , or % . Conceptually, this is just taking two numbers and applying the...

Practice › Codeforces Solutions › Surprise Language Round 7 ›

CF 470B - Hexakosioihexekontahexaphobia

CF 470B - Hexakosioihexekontahexaphobia Rating: 1800 Tags: *special Solve time: 1m 6s Verified: yes Solution Problem Understanding We are given a string consisting solely of digits, and the task is to determine if the number "666" appears anywhere as a contiguous sequence inside that string. The output should be "YES" if it does, and "NO" otherwise. This is a pattern-detection problem rather than a numerical computation problem, so the actual...

Practice › Codeforces Solutions › Surprise Language Round 7 ›

CF 470H - Array Sorting

CF 470H - Array Sorting Rating: 2300 Tags: *special Solve time: 1m 18s Verified: yes Solution Problem Understanding We are given an array of integers. The first number in the input is the array size n , and the next n integers are the array elements. The task is simply to output the same elements arranged in non-decreasing order. Although this problem appeared as a joke problem connected to the...

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CF 470D - Caesar Cipher

CF 470D - Caesar Cipher Rating: 1900 Tags: *special Solve time: 1m 24s Verified: yes Solution Problem Understanding We are asked to implement a simple Caesar cipher. The input gives us a key k , an integer between 0 and 25, which represents how many positions each letter in the message should be shifted forward in the alphabet. The message itself is a string of uppercase Latin letters, and its...

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CF 470A - Crystal Ball Sequence

CF 470A - Crystal Ball Sequence Rating: 1400 Tags: *special, implementation Solve time: 1m 36s Verified: yes Solution Problem Understanding The sequence in this problem comes from counting lattice points inside a growing hexagon on a hexagonal grid. Instead of having to construct the hexagon or count points manually, the problem already gives the formula for the sequence: $$H_n = 3 \cdot n \cdot (n+1) + 1$$ The input consists...

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CF 470E - Chessboard

CF 470E - Chessboard Rating: 1900 Tags: *special Solve time: 1m 29s Verified: yes Solution Problem Understanding We need to print an n × n chessboard using characters. White squares are represented by . and black squares by # . The square in the top-left corner is white, and colors alternate both horizontally and vertically exactly as on a real chessboard. The input contains a single integer n , which...

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CF 158C - Cd and pwd commands

CF 158C - Cd and pwd commands Rating: 1400 Tags: *special, data structures, implementation Solve time: 1m 45s Verified: yes Solution Problem Understanding We need to simulate a tiny shell that supports only two commands. The command cd path changes the current directory. The path may be absolute, meaning it starts from the root / , or relative, meaning it starts from the current directory. Inside a path, the token...

Practice › Codeforces Solutions › VK Cup 2012 Qualification Round 2 ›

CF 159B - Matchmaker

CF 159B - Matchmaker Rating: 1100 Tags: *special, greedy, sortings Solve time: 2m 1s Verified: yes Solution Problem Understanding We have two collections of objects. Markers are described by (color, diameter) and caps are also described by (color, diameter) . A cap can be attached to a marker only if the diameters are equal. Among all valid pairings, some are considered “beautiful” when the colors also match. The optimization goal...

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CF 162F - Factorial zeros

CF 162F - Factorial zeros Rating: 1800 Tags: *special Solve time: 1m 3s Verified: yes Solution Problem Understanding The task is to determine how many trailing zeros appear at the end of the factorial of a given integer n . A factorial, denoted n! , is the product of all integers from 1 up to n . Trailing zeros are the consecutive zeros at the rightmost end of this number,...

Practice › Codeforces Solutions › April Fools Day Contest 2013 ›

CF 290C - WTF?

CF 290C - WTF? Rating: 1700 Tags: *special, graph matchings, implementation, trees Solve time: 1m 31s Verified: yes Solution Problem Understanding The statement is written as a LOLCODE program. The actual task is to understand what this program computes. The input is a sequence of digits between 0 and 9 , one per line. The program repeatedly reads numbers until it encounters 0 . During the process it maintains four...

Practice › Codeforces Solutions › April Fools Day Contest 2014 ›

CF 409D - Big Data

CF 409D - Big Data Rating: 1700 Tags: *special Solve time: 1m 2s Verified: no Solution

Practice › Codeforces Solutions › Croc Champ 2013 - Qualification Round ›

CF 291B - Command Line Arguments

CF 291B - Command Line Arguments Rating: 1300 Tags: *special, implementation, strings Solve time: 1m 26s Verified: yes Solution Problem Understanding We are given a single string representing a command line in a simplified Pindows operating system. Each "lexeme" in this command line is either a contiguous sequence of non-space characters or a sequence of characters enclosed in double quotes. The first lexeme is the program name, and all subsequent...

Practice › Codeforces Solutions › VK Cup 2012 Qualification Round 1 ›

CF 158E - Phone Talks

CF 158E - Phone Talks Rating: 1900 Tags: *special, dp, sortings Solve time: 1m 13s Verified: yes Solution Problem Understanding We are asked to schedule a day of phone calls for Mr. Jackson in a way that maximizes the longest uninterrupted segment of sleep. Each call has a specific start time and duration. If a call arrives while he is already busy, it is queued and handled immediately after finishing...

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Friday the 13th, Programmers Day

Friday the 13th, Programmers Day Type: Special | Problems: 3 | Verified: 2/3 | Rating range: 1500-2700 | Time: 5m 36s Problem Name Rating Tags Solve Time Verified A Expecting Trouble 1500 *special, probabilities 1m 31s ✓ D Chain Letter 2200 *special, dfs-and-similar, graphs 2m 12s ✓ F Superstitions Inspection 2700 *special 1m 53s ✗

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April Fools Day Contest 2013

April Fools Day Contest 2013 Type: April Fools | Problems: 4 | Verified: 3/4 | Rating range: 1400-2800 | Time: 6m 44s Problem Name Rating Tags Solve Time Verified C WTF? 1700 *special, graph-matchings, implementation 1m 31s ✓ D Orange 1400 *special, implementation 2m 11s ✗ E HQ 2500 *special, constructive-algorithms 1m 43s ✓ F Greedy Petya 2800 *special, dfs-and-similar, graphs 1m 19s ✓

Practice › Codeforces Solutions › April Fools Day Contest 2014 ›

CF 409F - 000001

CF 409F - 000001 Rating: 1900 Tags: *special Solve time: 6m 57s Verified: no Solution Problem Understanding We are given a single integer a , and we need to compute a number that depends only on this value. The input is small enough that the answer is expected to be derived from a direct mathematical pattern rather than any simulation or search. Since there is only one parameter, the problem...

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CF 290E - HQ

CF 290E - HQ Rating: 2500 Tags: *special, constructive algorithms Solve time: 1m 43s Verified: yes Solution Problem Understanding The original HQ9+ language has several commands with special behavior. This problem asks about a reduced version called HQ..., and the destroyed statement leaves only enough clues to reconstruct the intended task. We are given a single string representing a program. We must determine whether this program produces output. In the...

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CF 162I - Truncatable primes

CF 162I - Truncatable primes Rating: 2000 Tags: *special Solve time: 1m 22s Verified: yes Solution Problem Understanding We are given a single integer and must decide whether it satisfies a very specific prime property. A number is considered truncatable if every suffix formed by repeatedly removing the leftmost digit is still prime. For example, starting from 9137 , we check: 9137 , 137 , 37 , 7 All four...

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CF 172E - BHTML+BCSS

CF 172E - BHTML+BCSS Rating: 2200 Tags: *special, dfs and similar, expression parsing Solve time: 2m 21s Verified: no Solution Problem Understanding We are given a simplified HTML-like document. Every tag is either an opening tag like <a> , a closing tag like </a> , or a self-closing tag like <a/> . The document is guaranteed to be properly nested, so every opening tag has exactly one matching closing tag....

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CF 162J - Brackets

CF 162J - Brackets Rating: 1800 Tags: *special Solve time: 1m 4s Verified: yes Solution Problem Understanding We are given a string consisting solely of opening and closing round brackets. The task is to determine whether this sequence is balanced, meaning it could represent a correct arrangement of parentheses in a mathematical expression. In other words, every opening bracket must have a matching closing bracket, and brackets must be properly...

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Croc Champ 2012 - Qualification Round

Croc Champ 2012 - Qualification Round Type: Special | Problems: 5 | Verified: 4/5 | Rating range: 800-2200 | Time: 11m 42s Problem Name Rating Tags Solve Time Verified A Phone Code 800 *special, brute-force, implementation 3m ✓ B Pseudorandom Sequence Period 1200 *special, implementation, number-theory 3m 33s ✓ C Bus 1500 *special, implementation, sortings 1m 19s ✓ D Calendar Reform 1500 *special, number-theory 1m 29s ✓ E BHTML+BCSS 2200...

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CF 172B - Pseudorandom Sequence Period

CF 172B - Pseudorandom Sequence Period Rating: 1200 Tags: *special, implementation, number theory Solve time: 3m 33s Verified: yes Solution Problem Understanding We are given a linear congruential generator, a classic pseudorandom sequence formula: $$r_i = (a \cdot r_{i-1} + b) \bmod m$$ The sequence starts from r0 , and every next value is computed from the previous one. Since every value is taken modulo m , there are only...

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CF 158D - Ice Sculptures

CF 158D - Ice Sculptures Rating: 1300 Tags: *special, brute force, number theory Solve time: 1m 38s Verified: yes Solution Problem Understanding We have n ice sculptures placed evenly on a circle. Each sculpture has a value, which may be positive or negative. We may remove some sculptures, but the remaining ones must still form a regular polygon. Because the sculptures cannot move, the remaining vertices must be equally spaced...

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CF 162B - Binary notation

CF 162B - Binary notation Rating: 1800 Tags: *special Solve time: 1m 20s Verified: yes Solution Problem Understanding We are given a single positive integer and must print its representation in base 2. In other words, instead of expressing the number as powers of 10, we express it as powers of 2 using only digits 0 and 1 . For example, the decimal number 5 becomes 101 because: $$5 =...

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CF 159C - String Manipulation 1.0

CF 159C - String Manipulation 1.0 Rating: 1400 Tags: *special, binary search, brute force, data structures, strings Solve time: 1m 31s Verified: yes Solution Problem Understanding We are given a string s and an integer k . The user initially registers a username t which is simply the string s repeated k times consecutively. After that, a sequence of edits occurs, each removing the p -th occurrence of a specified...

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VK Cup 2012 Qualification Round 1

VK Cup 2012 Qualification Round 1 Type: Special | Problems: 5 | Verified: 5/5 | Rating range: 800-1900 | Time: 7m 26s Problem Name Rating Tags Solve Time Verified A Next Round 800 *special, implementation 1m 29s ✓ B Taxi 1100 *special, greedy, implementation 1m 21s ✓ C Cd and pwd commands 1400 *special, data-structures, implementation 1m 45s ✓ D Ice Sculptures 1300 *special, brute-force, number-theory 1m 38s ✓ E...

Practice › Codeforces Solutions › Friday the 13th, Programmers Day ›

CF 345A - Expecting Trouble

CF 345A - Expecting Trouble Rating: 1500 Tags: *special, probabilities Solve time: 1m 31s Verified: yes Solution Problem Understanding We are given a sequence of recollections of Fridays the 13th. Each day is represented by a character: "0" for a normal day, "1" for a bad day, and "?" for an unknown day. Along with this sequence, we are provided a probability p that a "?" corresponds to a bad...

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Surprise Language Round 5

Surprise Language Round 5 Type: Special | Problems: 5 | Verified: 4/5 | Rating range: 1600-2200 | Time: 6m 19s Problem Name Rating Tags Solve Time Verified A A + B 1600 *special 59s ✓ B Binary notation 1800 *special 1m 29s ✓ C Caesar Cipher 2200 *special 1m 2s ✓ D Date Change 2000 *special 1m 16s ✓ E Euclidean Distance 2100 *special 1m 33s ✗

Practice › Codeforces Solutions › Croc Champ 2012 - Qualification Round ›

CF 172C - Bus

CF 172C - Bus Rating: 1500 Tags: *special, implementation, sortings Solve time: 1m 19s Verified: yes Solution Problem Understanding We are asked to simulate the operation of a single bus that repeatedly transports students from a bus stop at coordinate 0 to their respective destinations along the positive axis. Each student arrives at the stop at a distinct time and has a fixed destination coordinate. The bus can carry at...

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CF 290F - Greedy Petya

CF 290F - Greedy Petya Rating: 2800 Tags: *special, dfs and similar, graphs, greedy Solve time: 1m 19s Verified: yes Solution Problem Understanding The statement is intentionally misleading. We are not asked to solve the Hamiltonian path problem ourselves. Instead, we must reproduce the output of Petya’s supposedly correct program. That changes the task completely. The graph is undirected and may contain repeated edges or self-loops. We receive up to...

Practice › Codeforces Solutions › VK Cup 2012 Qualification Round 2 ›

CF 159E - Zebra Tower

CF 159E - Zebra Tower Rating: 1700 Tags: *special, data structures, greedy, sortings Solve time: 2m 2s Verified: yes Solution Problem Understanding We have n cubes. Every cube has a color and a size. We want to build a tower using cubes from exactly two distinct colors, and adjacent cubes in the tower must always have different colors. There are no restrictions on cube sizes or ordering. A smaller cube...

Practice › Codeforces Solutions › VK Cup 2012 Qualification Round 1 ›

CF 158A - Next Round

CF 158A - Next Round Rating: 800 Tags: *special, implementation Solve time: 1m 29s Verified: yes Solution Problem Understanding We are given the final standings of a programming contest. The scores are already sorted in non-increasing order, meaning each participant has a score greater than or equal to the next participant. A participant advances to the next round if two conditions are true. Their score must be at least as...

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CF 409H - A + B Strikes Back

CF 409H - A + B Strikes Back Rating: 1500 Tags: *special, brute force, constructive algorithms, dsu, implementation Solve time: 33s Verified: no Solution

Practice › Codeforces Solutions › Surprise Language Round 5 ›

CF 153C - Caesar Cipher

CF 153C - Caesar Cipher Rating: 2200 Tags: *special Solve time: 1m 2s Verified: yes Solution Problem Understanding We are asked to implement a Caesar cipher on an input string of uppercase Latin letters. Conceptually, this means each letter is shifted forward in the alphabet by a fixed number of positions, denoted by k . If the shift goes past 'Z', it wraps around to 'A'. For example, with a...

Practice › Codeforces Solutions › Friday the 13th, Programmers Day ›

CF 345F - Superstitions Inspection

CF 345F - Superstitions Inspection Rating: 2700 Tags: *special Solve time: 1m 53s Verified: no Solution Problem Understanding The input describes a collection of countries, where each country is followed by a list of superstition names observed in that country. Each superstition is written as a line starting with an asterisk, and names may contain multiple words separated by irregular spacing. Countries appear as standalone lines without the asterisk prefix....

Practice › Codeforces Solutions › Croc Champ 2013 - Qualification Round ›

CF 291E - Tree-String Problem

CF 291E - Tree-String Problem Rating: 2000 Tags: *special, dfs and similar, hashing, strings Solve time: 1m 51s Verified: yes Solution Problem Understanding We have a rooted tree with root 1 . Every edge from a parent to a child contains a lowercase string. If we walk downward through the tree and read characters along the edges, we obtain a long text embedded into the tree. A position is not...

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Coder-Strike 2014 - Qualification Round

Coder-Strike 2014 - Qualification Round Type: Special | Problems: 1 | Verified: 0/1 | Rating range: 1700-1700 | Time: 11m 4s Problem Name Rating Tags Solve Time Verified C Kicker 1700 *special, implementation 11m 4s ✗

Practice › Codeforces Solutions › April Fools Day Contest 2013 ›

CF 290D - Orange

CF 290D - Orange Rating: 1400 Tags: *special, implementation Solve time: 2m 11s Verified: no Solution Problem Understanding We are given a string consisting of uppercase and lowercase English letters, and an integer k . The task is to modify the string so that exactly k characters become uppercase. The relative order of characters must stay unchanged, only the letter cases may change. The tricky part is that the original...

Practice › Codeforces Solutions › April Fools Day Contest ›

CF 171B - Star

CF 171B - Star Rating: 1300 Tags: *special, combinatorics Solve time: 2m 57s Verified: yes Solution Problem Understanding In this problem, we are asked to calculate the total number of cells in a star-shaped pattern drawn on a grid, given a number of layers. The input is a single integer a , representing the number of concentric layers in the star. The output is a single integer, which is the...

Practice › Codeforces Solutions › Surprise Language Round 6 ›

CF 188E - HQ9+

CF 188E - HQ9+ Rating: 1400 Tags: *special, implementation Solve time: 1m 17s Verified: yes Solution Problem Understanding We are given a single string representing a program written in the joke language HQ9+. Most characters do nothing, but four specific uppercase characters are meaningful. The instruction H prints "Hello, World!" , the instruction Q prints the program itself, and the instruction 9 prints the lyrics of "99 Bottles of Beer"...

Practice › Codeforces Solutions › Croc Champ 2012 - Qualification Round ›

CF 172A - Phone Code

CF 172A - Phone Code Rating: 800 Tags: *special, brute force, implementation Solve time: 3m Verified: yes Solution Problem Understanding We are given a list of phone numbers from friends in a city. Each phone number is a string of digits, and all numbers have the same length. The task is to find the city phone code, which Polycarpus defines as the longest common prefix shared by all these numbers....

Practice › Codeforces Solutions › April Fools Day Contest ›

CF 171C - A Piece of Cake

CF 171C - A Piece of Cake Rating: 2000 Tags: *special, implementation Solve time: 1m 30s Verified: yes Solution Problem Understanding The input is a sequence of integers. The first number tells us how many additional integers follow. If the sequence is: 4 1 2 3 4 then there are four values: 1, 2, 3, 4 . The task itself is intentionally disguised by the strange statement. The actual operation...

Practice › Codeforces Solutions › VK Cup 2012 Qualification Round 1 ›

CF 158B - Taxi

CF 158B - Taxi Rating: 1100 Tags: *special, greedy, implementation Solve time: 1m 21s Verified: yes Solution Problem Understanding We have a collection of schoolchildren organized into groups, and each group wants to travel together in a taxi. Each group has between one and four children, and each taxi can carry at most four children. The goal is to determine the minimum number of taxis required to transport all groups...

Practice › Codeforces Solutions › Surprise Language Round 6 ›

CF 188B - A + Reverse B

CF 188B - A + Reverse B Rating: 1300 Tags: *special, implementation Solve time: 1m 55s Verified: yes Solution Problem Understanding We are asked to compute the sum of a number a and the reverse of another number b . Reversing a number means reading its digits from right to left and treating the result as an integer. For instance, reversing 230 yields 32 because leading zeros are discarded in...

Practice › Codeforces Solutions ›

April Fools Day Contest 2014

April Fools Day Contest 2014 Type: April Fools | Problems: 6 | Verified: 0/6 | Rating range: 1500-2200 | Time: 15m 44s Problem Name Rating Tags Solve Time Verified A The Great Game 1700 *special 4m 22s ✗ B Mysterious Language 1700 *special 57s ✗ D Big Data 1700 *special 1m 2s ✗ F 000001 1900 *special 6m 57s ✗ G On a plane 2200 *special, geometry 1m 53s ✗...

Practice › Codeforces Solutions › Friday the 13th, Programmers Day ›

CF 345D - Chain Letter

CF 345D - Chain Letter Rating: 2200 Tags: *special, dfs and similar, graphs Solve time: 2m 12s Verified: yes Solution Problem Understanding We are asked to simulate the spread of a chain letter through a network of friends. Each person is represented as a node in a graph, and the connections between people-who sends letters to whom-are given as an adjacency matrix of "0" and "1" characters. The graph is...

Practice › Codeforces Solutions ›

Croc Champ 2013 - Qualification Round

Croc Champ 2013 - Qualification Round Type: Special | Problems: 2 | Verified: 2/2 | Rating range: 1300-2000 | Time: 3m 17s Problem Name Rating Tags Solve Time Verified B Command Line Arguments 1300 *special, implementation, strings 1m 26s ✓ E Tree-String Problem 2000 *special, dfs-and-similar, hashing 1m 51s ✓

Practice › Codeforces Solutions › April Fools Day Contest 2014 ›

CF 409A - The Great Game

CF 409A - The Great Game Rating: 1700 Tags: *special Solve time: 4m 22s Verified: no Solution Problem Understanding In this problem, we are given two strings of equal length, each representing a sequence of actions taken by two competing teams in a hypothetical game. Each character corresponds to a distinct type of action, and each action has a predetermined score. Our goal is to compare the cumulative scores of...

Practice › Codeforces Solutions ›

VK Cup 2012 Wild-card Round 1

VK Cup 2012 Wild-card Round 1 Type: Special | Problems: 10 | Verified: 9/10 | Rating range: 1100-2000 | Time: 16m 36s Problem Name Rating Tags Solve Time Verified A Pentagonal numbers 1100 *special, implementation 3m 10s ✓ B Binary notation 1800 *special 1m 20s ✓ C Prime factorization 1800 *special 1m 16s ✓ D Remove digits 1900 *special 1m 15s ✓ E HQ9+ 1800 *special 1m 9s ✓ F...

Practice › Codeforces Solutions › April Fools Day Contest 2014 ›

CF 409G - On a plane

CF 409G - On a plane Rating: 2200 Tags: *special, geometry Solve time: 1m 53s Verified: no Solution Problem Understanding We are given a set of points on a two-dimensional plane, each with real-valued coordinates. The task is to find the largest possible angle formed at the origin by any three of these points, where the origin serves as the vertex and the rays extend to the selected points. The...

Practice › Codeforces Solutions › Surprise Language Round 6 ›

CF 188F - Binary Notation

CF 188F - Binary Notation Rating: 1400 Tags: *special, implementation Solve time: 1m 32s Verified: yes Solution Problem Understanding We are given a single positive integer and must print its representation in base 2. In other words, instead of writing the number using decimal digits from 0 to 9, we must write it using only binary digits, 0 and 1. For example, the decimal number 5 becomes 101 in binary...

Practice › Codeforces Solutions › Surprise Language Round 5 ›

CF 153D - Date Change

CF 153D - Date Change Rating: 2000 Tags: *special Solve time: 1m 16s Verified: yes Solution Problem Understanding We are asked to manipulate dates by adding or subtracting a number of days. The input consists of a date string in the "DD.MM.YYYY" format and an integer representing a shift in days, which can be positive or negative. The output is a date string in the same format representing the original...

Practice › Codeforces Solutions › Surprise Language Round 5 ›

CF 153A - A + B

CF 153A - A + B Rating: 1600 Tags: *special Solve time: 59s Verified: yes Solution Problem Understanding We are asked to compute the sum of two integers, but the emphasis is on careful output formatting. Specifically, the input consists of two numbers, each on its own line, and we need to print their sum without any leading zeros. This means that even if the sum is, for example, 00015...

Practice › Codeforces Solutions › VK Cup 2012 Wild-card Round 1 ›

CF 162G - Non-decimal sum

CF 162G - Non-decimal sum Rating: 2000 Tags: *special Solve time: 1m 46s Verified: yes Solution Problem Understanding We are given several integers written in an arbitrary base between 2 and 36. Digits above 9 are represented with uppercase letters, so in base 16 the digit sequence continues as A, B, C, D, E, F , and in larger bases it may continue up to Z . The task is...

Practice › Codeforces Solutions ›

VK Cup 2012 Qualification Round 2

VK Cup 2012 Qualification Round 2 Type: Special | Problems: 5 | Verified: 5/5 | Rating range: 1100-1700 | Time: 8m 47s Problem Name Rating Tags Solve Time Verified A Friends or Not 1400 *special, greedy, implementation 1m 47s ✓ B Matchmaker 1100 *special, greedy, sortings 2m 1s ✓ C String Manipulation 1.0 1400 *special, binary-search, brute-force 1m 31s ✓ D Palindrome pairs 1500 *special, brute-force, dp 1m 26s ✓...

Practice › Codeforces Solutions › Croc Champ 2012 - Qualification Round ›

CF 172D - Calendar Reform

CF 172D - Calendar Reform Rating: 1500 Tags: *special, number theory Solve time: 1m 29s Verified: yes Solution Problem Understanding Each year in Berland has a certain number of days. The first year has a days, the next has a + 1 , and so on for n consecutive years. For a year with x days, the government chooses a month length that satisfies two conditions. First, the month length...

Practice › Codeforces Solutions › VK Cup 2012 Wild-card Round 1 ›

CF 162H - Alternating case

CF 162H - Alternating case Rating: 1800 Tags: *special Solve time: 3m 11s Verified: no Solution Problem Understanding We are given a single string containing English letters in arbitrary capitalization. The task is to rewrite the string so that characters at odd positions become uppercase and characters at even positions become lowercase. The positions are counted starting from 1, not from 0. For example, if the input is Codeforces ,...

Practice › Codeforces Solutions › Surprise Language Round 6 ›

CF 188C - LCM

CF 188C - LCM Rating: 1400 Tags: *special, implementation, math Solve time: 1m 59s Verified: yes Solution Problem Understanding We are given two positive integers and need to compute their least common multiple. The least common multiple, usually abbreviated as LCM, is the smallest positive integer that both numbers divide evenly. For example, if the numbers are 10 and 42, the answer is 210 because 210 is divisible by both...

Practice › Codeforces Solutions › VK Cup 2012 Qualification Round 2 ›

CF 159D - Palindrome pairs

CF 159D - Palindrome pairs Rating: 1500 Tags: *special, brute force, dp, strings Solve time: 1m 26s Verified: yes Solution Problem Understanding We are given a string of lowercase letters and need to count the number of pairs of non-overlapping palindromic substrings. Formally, we are looking for tuples (a, b, x, y) such that the substring from a to b and the substring from x to y are both palindromes...

Practice › Codeforces Solutions › VK Cup 2012 Wild-card Round 1 ›

CF 162D - Remove digits

CF 162D - Remove digits Rating: 1900 Tags: *special Solve time: 1m 15s Verified: yes Solution Problem Understanding We are given a single string containing printable ASCII characters. Some of those characters may be digits from '0' to '9' . The task is to remove every digit and print the remaining characters in their original order. The statement mentions that characters shift left after removal, but that detail only describes...

Practice › Codeforces Solutions › Coder-Strike 2014 - Qualification Round ›

CF 411C - Kicker

CF 411C - Kicker Rating: 1700 Tags: *special, implementation Solve time: 11m 4s Verified: no Solution Problem Understanding We are given four players split into two fixed teams of two players each. Each player has two independent strengths: one for defence and one for attack. Before the match, each team must assign one of its players to attack and the other to defend. Once both teams have chosen roles, we...

Practice › Codeforces Solutions › April Fools Day Contest 2014 ›

CF 409B - Mysterious Language

CF 409B - Mysterious Language Rating: 1700 Tags: *special Solve time: 57s Verified: no Solution

Practice › Codeforces Solutions › Surprise Language Round 5 ›

CF 153E - Euclidean Distance

CF 153E - Euclidean Distance Rating: 2100 Tags: *special Solve time: 1m 33s Verified: no Solution Problem Understanding We are given up to 50 points on a 2D plane. Each point has integer coordinates, and some points may coincide. The task is to find the largest Euclidean distance between any pair of points. For two points $(x_1, y_1)$ and $(x_2, y_2)$, the Euclidean distance is: $d=\sqrt{(x_1-x_2)^2+(y_1-y_2)^2}$Drag the points to update...

Practice › Codeforces Solutions › VK Cup 2012 Wild-card Round 1 ›

CF 162E - HQ9+

CF 162E - HQ9+ Rating: 1800 Tags: *special Solve time: 1m 9s Verified: yes Solution Problem Understanding The problem asks whether a program written in the joke language HQ9+ will produce any output. The program is a string containing between 1 and 100 printable ASCII characters. Only four instructions matter: "H", "Q", "9", and "+". The "+" instruction manipulates an internal accumulator but does not produce any output, so it...

Practice › Codeforces Solutions ›

Surprise Language Round 6

Surprise Language Round 6 Type: Special | Problems: 4 | Verified: 4/4 | Rating range: 1300-1400 | Time: 6m 43s Problem Name Rating Tags Solve Time Verified B A + Reverse B 1300 *special, implementation 1m 55s ✓ C LCM 1400 *special, implementation, math 1m 59s ✓ E HQ9+ 1400 *special, implementation 1m 17s ✓ F Binary Notation 1400 *special, implementation 1m 32s ✓

Practice › Codeforces Solutions › VK Cup 2012 Wild-card Round 1 ›

CF 162C - Prime factorization

CF 162C - Prime factorization Rating: 1800 Tags: *special Solve time: 1m 16s Verified: yes Solution Problem Understanding We are asked to take a positive integer and express it as a product of prime numbers, showing each prime the number of times it appears in the factorization. For example, the number 245 can be expressed as 5 multiplied by 7 twice, so the output would be 5_7_7. The input is...

Practice › Codeforces Solutions › VK Cup 2012 Qualification Round 2 ›

CF 159A - Friends or Not

CF 159A - Friends or Not Rating: 1400 Tags: *special, greedy, implementation Solve time: 1m 47s Verified: yes Solution Problem Understanding We are given a chronological log of private messages between users in a social network. Each record contains the sender, the receiver, and the timestamp of the message. Two users become friends if one of them replies to the other's message quickly enough. More precisely, suppose user A sends...

Practice › Codeforces Solutions › VK Cup 2012 Wild-card Round 1 ›

CF 162A - Pentagonal numbers

CF 162A - Pentagonal numbers Rating: 1100 Tags: *special, implementation Solve time: 3m 10s Verified: yes Solution Problem Understanding We need to compute the n -th pentagonal number. Pentagonal numbers form a sequence generated by a direct mathematical formula: $$P_n = \frac{3n^2 - n}{2}$$ The input contains a single integer n , and the output is the value of this formula for that position in the sequence. The constraints are...

Practice › Codeforces Solutions › Surprise Language Round 5 ›

CF 153B - Binary notation

CF 153B - Binary notation Rating: 1800 Tags: *special Solve time: 1m 29s Verified: yes Solution Problem Understanding We are given a single positive integer and must print its representation in base 2. In other words, we want to express the number as powers of two and output the corresponding sequence of bits. For example, the decimal number 13 is equal to: $13 = 1\cdot2^3 + 1\cdot2^2 + 0\cdot2^1 +...

Practice › Codeforces Solutions ›

Unknown Language Round 4

Unknown Language Round 4 Type: Special | Problems: 10 | Verified: 10/10 | Rating range: 900-2300 | Time: 16m 22s Problem Name Rating Tags Solve Time Verified A Hexagonal numbers 900 *special, implementation 1m 24s ✓ B Gnikool Ssalg 1400 *special, implementation, strings 1m 24s ✓ C Decimal sum 1500 *special 1m 48s ✓ D Exponentiation 1500 *special 1m 51s ✓ E Tribonacci numbers 1600 *special 2m 6s ✓ F...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130C - Decimal sum

CF 130C - Decimal sum Rating: 1500 Tags: *special Solve time: 1m 48s Verified: yes Solution Problem Understanding We are given a sequence of integers and need to compute their total sum. The input starts with an integer n , which tells us how many numbers follow. Each of the next n lines contains one element of the array. The task is simply to add all of them together and...

Practice › Codeforces Solutions › Unknown Language Round 1 ›

CF 64C - Table

CF 64C - Table Rating: 1600 Tags: *special, greedy, implementation, math Solve time: 1m 25s Verified: yes Solution Problem Understanding We are given an $n \times m$ table filled with consecutive integers starting from 1. The filling is done row by row, left to right. For example, if $n=3$ and $m=4$, the table looks like this: 1 2 3 4 5 6 7 8 9 10 11 12 Then, the...

Practice › Codeforces Solutions › Unknown Language Round 2 ›

CF 72B - INI-file

CF 72B - INI-file Rating: 2200 Tags: *special, implementation Solve time: 1m 45s Verified: yes Solution Problem Understanding We are given a text file written in INI format. Every meaningful line is either a section declaration such as [network] or a key-value assignment such as port=8080 . Spaces around keys, values, and section brackets are irrelevant and must be removed in the final output. Lines whose first non-space character is...

Practice › Codeforces Solutions ›

Unknown Language Round 2

Unknown Language Round 2 Type: Special | Problems: 9 | Verified: 8/9 | Rating range: 1000-2300 | Time: 21m 37s Problem Name Rating Tags Solve Time Verified A Goshtasp, Vishtasp and Eidi 1800 *special, greedy, math 1m 18s ✓ B INI-file 2200 *special, implementation 1m 45s ✓ C Extraordinarily Nice Numbers 1200 *special, math 1m 26s ✓ D Perse-script 2300 *special, expression-parsing 1m 55s ✗ E Ali goes shopping 1800...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130J - Date calculation

CF 130J - Date calculation Rating: 1800 Tags: *special Solve time: 1m 30s Verified: yes Solution Problem Understanding We are given a year in the Gregorian calendar and a day number inside that year. The task is to determine the actual calendar date corresponding to that day number. For example, if the input year is 2011 and the day index is 324, we count forward from January 1st until we...

Practice › Codeforces Solutions › Unknown Language Round 2 ›

CF 72I - Goofy Numbers

CF 72I - Goofy Numbers Rating: 1500 Tags: *special, implementation Solve time: 1m 12s Verified: yes Solution Problem Understanding We are asked to classify a single non-negative integer based on how it relates to its digits. Specifically, each digit of the number is considered as a potential divisor. The integer falls into one of three categories: it is happier if it is divisible by every non-zero digit, happy if it...

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100A - Carpeting the Room

CF 100A - Carpeting the Room Rating: 1100 Tags: *special, implementation Solve time: 2m 19s Verified: yes Solution Problem Understanding We have a square room with side length n , so the total area is n × n . We also have k square carpets, each with side length n1 . Every carpet always stays axis-aligned because rotation is forbidden, but since the carpets are squares, rotation would not actually...

Practice › Codeforces Solutions ›

Unknown Language Round 1

Unknown Language Round 1 Type: Special | Problems: 9 | Verified: 9/9 | Rating range: 1300-2400 | Time: 14m 26s Problem Name Rating Tags Solve Time Verified A Factorial 1300 *special, implementation 1m 13s ✓ B Expression 1500 *special, expression-parsing 1m 39s ✓ C Table 1600 *special, greedy, implementation 1m 25s ✓ D Presents 1800 *special, greedy 1m 40s ✓ E Prime Segment 1800 *special, brute-force, math 1m 28s ✓...

Practice › Codeforces Solutions › Unknown Language Round 2 ›

CF 72A - Goshtasp, Vishtasp and Eidi

CF 72A - Goshtasp, Vishtasp and Eidi Rating: 1800 Tags: *special, greedy, math Solve time: 1m 18s Verified: yes Solution Problem Understanding The problem asks us to decide whether a positive integer $n$ can be represented as a sum of distinct integers, where each integer is either 1 or a prime number. If such a representation exists, we need to produce one that is lexicographically largest. Lexicographically largest means that,...

Practice › Codeforces Solutions › Unknown Language Round 2 ›

CF 72G - Fibonacci army

CF 72G - Fibonacci army Rating: 1000 Tags: *special, dp Solve time: 1m 16s Verified: yes Solution Problem Understanding The problem asks us to compute the n -th Fibonacci number, but with a slight twist in indexing: the sequence starts with f₀ = 1, f₁ = 1. Every subsequent number is the sum of the previous two. In practical terms, if the king wants an army of size corresponding to...

Practice › Codeforces Solutions › Unknown Language Round 2 ›

CF 72H - Reverse It!

CF 72H - Reverse It! Rating: 1600 Tags: *special, implementation Solve time: 3m 28s Verified: yes Solution Problem Understanding The task is to reverse a number given as a string, taking care of signs and leading zeros. The input can be a very large integer, up to 10,000 digits, possibly with leading zeros. We need to remove those leading zeros first, reverse the remaining digits, and output the result as...

Practice › Codeforces Solutions › Unknown Language Round 1 ›

CF 64H - Table Bowling

CF 64H - Table Bowling Rating: 2300 Tags: *special, sortings Solve time: 1m 52s Verified: yes Solution Problem Understanding We are given the final standings of a table bowling tournament. Every participant has a unique name and an integer score. The task is not just to sort the players, but also to assign ranking labels in the style used in real tournaments. Players are ordered primarily by decreasing score. If...

Practice › Codeforces Solutions › Unknown Language Round 1 ›

CF 64B - Expression

CF 64B - Expression Rating: 1500 Tags: *special, expression parsing Solve time: 1m 39s Verified: yes Solution Problem Understanding The input is a tiny arithmetic expression written as a three-character string. The first and third characters are digits from 0 to 9 , and the middle character is either + or - . The task is to evaluate the expression and print the resulting integer. For example, the input 1-5...

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100D - World of Mouth

CF 100D - World of Mouth Rating: 1500 Tags: *special, strings Solve time: 2m 18s Verified: yes Solution Problem Understanding We start with an initial string and pass it around a circle of n people. Every person is allowed to modify the string in only one of two ways: Remove exactly one character from the end. Add exactly one character to the end. A person may also choose to do...

Practice › Codeforces Solutions › Unknown Language Round 2 ›

CF 72E - Ali goes shopping

CF 72E - Ali goes shopping Rating: 1800 Tags: *special, brute force, strings Solve time: 7m 34s Verified: yes Solution Problem Understanding We are given a lowercase string and must find the substring that appears the largest number of times inside it. Occurrences may overlap. Among all substrings with the same maximum frequency, we choose the longest one. If there is still a tie, we choose the lexicographically largest substring....

Practice › Codeforces Solutions ›

Unknown Language Round 3

Unknown Language Round 3 Type: Special | Problems: 10 | Verified: 10/10 | Rating range: 1100-2400 | Time: 23m 31s Problem Name Rating Tags Solve Time Verified A Carpeting the Room 1100 *special, implementation 2m 19s ✓ B Friendly Numbers 1500 *special, implementation 2m 19s ✓ C A+B 1400 *special, implementation 1m 27s ✓ D World of Mouth 1500 *special, strings 2m 18s ✓ E Lamps in a Line 1600...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130F - Prime factorization

CF 130F - Prime factorization Rating: 1600 Tags: *special Solve time: 1m 48s Verified: yes Solution Problem Understanding The task is to decompose a given integer n into its prime factors and print them in non-decreasing order, with each prime repeated according to its multiplicity. Essentially, if a number is a product of primes like $n = 2^2 \cdot 3^1 \cdot 5^2$, the output should be 2 2 3 5...

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100F - Polynom

CF 100F - Polynom Rating: 1800 Tags: *special, implementation Solve time: 2m 26s Verified: yes Solution Problem Understanding We are given a polynomial already factorized into linear terms: $$p(x) = (x + a_1)(x + a_2)\dots(x + a_n)$$ The task is to expand this product and print the polynomial in the usual descending-power form: $$x^n + b_1x^{n-1} + \dots + b_n$$ The tricky part is not the expansion itself. The tricky...

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100E - Lamps in a Line

CF 100E - Lamps in a Line Rating: 1600 Tags: *special, math Solve time: 1m 35s Verified: yes Solution Problem Understanding We have a row of n lamps, each initially either on or off. Each lamp has a number from 1 to n . We also have n keys numbered the same way. Pressing key i toggles every lamp whose number is divisible by i . After a sequence of...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130E - Tribonacci numbers

CF 130E - Tribonacci numbers Rating: 1600 Tags: *special Solve time: 2m 6s Verified: yes Solution Problem Understanding We are asked to compute the n -th Tribonacci number, but only its value modulo 26 . The sequence starts with: $$t_0 = 0,\quad t_1 = 0,\quad t_2 = 1$$ and every later value is formed by summing the previous three: $$t_i = t_{i-1} + t_{i-2} + t_{i-3}$$ The input contains a...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130G - CAPS LOCK ON

CF 130G - CAPS LOCK ON Rating: 1700 Tags: *special Solve time: 1m 28s Verified: yes Solution Problem Understanding We are given a single string containing printable ASCII characters. Some characters may be lowercase English letters, some may already be uppercase letters, and others may be symbols or digits. The task is to transform only the lowercase letters into their uppercase versions while leaving every other character unchanged. For example,...

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100G - Name the album

CF 100G - Name the album Rating: 1800 Tags: *special, data structures, implementation Solve time: 1m 50s Verified: yes Solution Problem Understanding Aryo wants to choose a title for a new album from a list of candidate names. Some names have already been used in previous years. His decision rule has two layers. If a candidate name has never been used before, that is the best possible choice. Among all...

Practice › Codeforces Solutions › Unknown Language Round 1 ›

CF 64F - Domain

CF 64F - Domain Rating: 2000 Tags: *special, expression parsing Solve time: 1m 37s Verified: yes Solution Problem Understanding We need to decide whether a given string can be interpreted as a valid domain name under a simplified set of rules. The string may only contain lowercase English letters, digits, and dots. Dots separate the string into segments. The string cannot start with a dot or end with a dot,...

Practice › Codeforces Solutions › Unknown Language Round 1 ›

CF 64D - Presents

CF 64D - Presents Rating: 1800 Tags: *special, greedy Solve time: 1m 40s Verified: yes Solution Problem Understanding We are given three positive integers representing the prices of three presents. There are three sisters, ranked by age: eldest, middle, and youngest. The task is to assign each present to a sister according to the rule that the most expensive present goes to the eldest sister, the second most expensive to...

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100I - Rotation

CF 100I - Rotation Rating: 1500 Tags: *special, geometry, math Solve time: 4m 21s Verified: yes Solution Problem Understanding We are given a point $(x, y)$ on the 2D plane and an angle $k$ in degrees. The task is to rotate the point counter-clockwise around the origin by exactly $k$ degrees and print the coordinates of the new point. A rotation around the origin preserves the distance from the origin...

Practice › Codeforces Solutions › Unknown Language Round 1 ›

CF 64G - Path Canonization

CF 64G - Path Canonization Rating: 2200 Tags: *special Solve time: 1m 42s Verified: yes Solution Problem Understanding We are given an absolute Unix-style path. The path is split into components by / , and every component represents either a normal directory or file name, "." , or ".." . A normal name means “go into this directory or file”. The component "." means “stay in the current directory”, so...

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100J - Interval Coloring

CF 100J - Interval Coloring Rating: 2400 Tags: *special, greedy, math Solve time: 1m 52s Verified: yes Solution Problem Understanding We are asked to color a collection of intervals on the number line such that no three intervals with the same color form a "triple overlap pattern." More concretely, a coloring is invalid if there exist three intervals of the same color where each pair overlaps at some point in...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130D - Exponentiation

CF 130D - Exponentiation Rating: 1500 Tags: *special Solve time: 1m 51s Verified: yes Solution Problem Understanding We need to compute the remainder when $a^b$ is divided by $c$. The input gives three integers, one per line. The first value is the base, the second is the exponent, and the third is the modulus. The direct interpretation is straightforward. If the input is: 2 5 40 then we calculate $2^5...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130A - Hexagonal numbers

CF 130A - Hexagonal numbers Rating: 900 Tags: *special, implementation Solve time: 1m 24s Verified: yes Solution Problem Understanding We need to compute the $n$-th hexagonal number. The sequence is defined by the formula $$h_n = 2n^2 - n$$ The input contains a single integer $n$, and the output is the value produced by this formula. For example, when $n = 2$, $$h_2 = 2 \cdot 2^2 - 2 =...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130B - Gnikool Ssalg

CF 130B - Gnikool Ssalg Rating: 1400 Tags: *special, implementation, strings Solve time: 1m 24s Verified: yes Solution Problem Understanding The problem asks us to reverse a string. Given a sequence of characters, the output should be the same sequence but in the opposite order, so that the first character becomes the last, the second becomes the second-to-last, and so on. The input string is guaranteed to have between 1...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130I - Array sorting

CF 130I - Array sorting Rating: 2300 Tags: *special, sortings Solve time: 1m 47s Verified: yes Solution Problem Understanding We are given an array of at most 100 integers. Every value lies between 1 and 60. The task is simply to print the array in non-decreasing order. At first glance this looks like a standard sorting problem, but the unusually small value range changes the structure of the problem completely....

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100H - Battleship

CF 100H - Battleship Rating: 2100 Tags: *special, dfs and similar, implementation Solve time: 3m 4s Verified: yes Solution Problem Understanding We are given several 10 × 10 Battleship boards. Each cell is either empty or occupied by part of a ship. The task is to verify whether every occupied cell belongs to a valid fleet configuration. A valid Battleship fleet contains exactly one ship of length 4, two ships...

Practice › Codeforces Solutions › Unknown Language Round 2 ›

CF 72D - Perse-script

CF 72D - Perse-script Rating: 2300 Tags: *special, expression parsing Solve time: 1m 55s Verified: no Solution Problem Understanding We are asked to evaluate a string expression in a small function-based language. Every string literal is enclosed in quotes, and there are only four types of functions: concat , reverse , and substr in two forms. Each function operates only on strings or integers as indices. The input is a...

Practice › Codeforces Solutions › Unknown Language Round 4 ›

CF 130H - Balanced brackets

CF 130H - Balanced brackets Rating: 1600 Tags: *special Solve time: 1m 16s Verified: yes Solution Problem Understanding We are asked to determine if a string of round brackets is balanced. A balanced sequence is one where every opening bracket «(» has a corresponding closing bracket «)», and brackets are properly nested. In other words, if you were to traverse the string from left to right, at no point should...

Practice › Codeforces Solutions › Unknown Language Round 1 ›

CF 64A - Factorial

CF 64A - Factorial Rating: 1300 Tags: *special, implementation Solve time: 1m 13s Verified: yes Solution Problem Understanding We are asked to compute the factorial of a given integer $n$. Factorial is the product of all positive integers up to $n$, so for $n = 3$, the factorial is $1 \times 2 \times 3 = 6$. The input is a single integer, and the output is the single integer result...

Practice › Codeforces Solutions › Unknown Language Round 1 ›

CF 64I - Sort the Table

CF 64I - Sort the Table Rating: 2400 Tags: *special, sortings Solve time: 1m 50s Verified: yes Solution Problem Understanding We are given a table where every row contains several string fields, and the first input line tells us the name of each column. Another line describes how the rows should be ordered. Each rule has the form COLUMN_NAME ASC or COLUMN_NAME DESC . The sorting behaves exactly like a...

Practice › Codeforces Solutions › Unknown Language Round 2 ›

CF 72F - Oil

CF 72F - Oil Rating: 1900 Tags: *special, greedy, math Solve time: 1m 43s Verified: yes Solution Problem Understanding We have an n × m grid. Some entire rows are empty, some entire columns are empty, and every empty cell belongs to at least one of those empty rows or empty columns. All remaining cells contain oil. If we drill a well in one oil cell, we can reach every...

Practice › Codeforces Solutions › Unknown Language Round 2 ›

CF 72C - Extraordinarily Nice Numbers

CF 72C - Extraordinarily Nice Numbers Rating: 1200 Tags: *special, math Solve time: 1m 26s Verified: yes Solution Problem Understanding We are asked to determine whether a positive integer $x$ is extraordinarily nice. By the problem's definition, a number is extraordinarily nice if it has exactly the same number of even divisors as odd divisors. The input is a single integer $x$ between 1 and 1000. The output is simply...

Practice › Codeforces Solutions › Unknown Language Round 1 ›

CF 64E - Prime Segment

CF 64E - Prime Segment Rating: 1800 Tags: *special, brute force, math, number theory Solve time: 1m 28s Verified: yes Solution Problem Understanding We are asked to find the closest prime numbers surrounding a given integer n . Concretely, we need two numbers, a and b , such that a ≤ n ≤ b and both a and b are prime. Among all prime intervals containing n , the one...

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100C - A+B

CF 100C - A+B Rating: 1400 Tags: *special, implementation Solve time: 1m 27s Verified: yes Solution Problem Understanding The task looks trivial at first glance: read two integers and print their sum. The catch is hidden inside the constraints. Each number can contain up to 500 decimal digits, far larger than the range of standard 32-bit or 64-bit integers in many languages. We are given two positive integers, each written...

Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100B - Friendly Numbers

CF 100B - Friendly Numbers Rating: 1500 Tags: *special, implementation Solve time: 2m 19s Verified: yes Solution Problem Understanding We are asked to determine whether a set of non-zero integers forms a "friendly group," meaning every pair of numbers satisfies a divisibility relationship: one number divides the other. The input provides the number of integers, $n$, followed by a comma-separated list of the integers sorted in non-decreasing order. The output...

#*special

CF 171A - Mysterious numbers - 1

April Fools Day Contest

CF 171H - A polyline

CF 171G - Mysterious numbers - 2

CF 171F - ucyhf

CF 171E - MYSTERIOUS LANGUAGE

CF 171D - Broken checker

CF 1952I - Dark Matter

CF 1958I - Equal Trees

CF 1958A - 1-3-5

CF 1958J - Necromancer

CF 1952B - Is it stated?

Kotlin Heroes: Episode 10

CF 1958H - Composite Spells

CF 1952F - Grid

CF 1952A - Are You a Robot, Again?

CF 1958F - Narrow Paths

2023 Post World Finals Online ICPC Challenge powered by Huawei

CF 1952H - Palindrome

CF 1958B - Clock in the Pool

CF 1953A - Accuracy-Preserving Summation Algorithm

April Fools Day Contest 2024

CF 1958C - Firewood

CF 1952C - They Have Fooled

CF 1958E - Yet Another Permutation Constructive

CF 1958G - Observation Towers

CF 1952G - Mathematician Takeover

CF 1958D - Staircase

Surprise Language Round 7

CF 470F - Pairwise Sums

CF 470G - Hamming Distance

CF 470C - Eval

CF 470B - Hexakosioihexekontahexaphobia

CF 470H - Array Sorting

CF 470D - Caesar Cipher

CF 470A - Crystal Ball Sequence

CF 470E - Chessboard

CF 158C - Cd and pwd commands

CF 159B - Matchmaker

CF 162F - Factorial zeros

CF 290C - WTF?

CF 409D - Big Data

CF 291B - Command Line Arguments

CF 158E - Phone Talks

Friday the 13th, Programmers Day

April Fools Day Contest 2013

CF 409F - 000001

CF 290E - HQ

CF 162I - Truncatable primes

CF 172E - BHTML+BCSS

CF 162J - Brackets

Croc Champ 2012 - Qualification Round

CF 172B - Pseudorandom Sequence Period

CF 158D - Ice Sculptures

CF 162B - Binary notation

CF 159C - String Manipulation 1.0

VK Cup 2012 Qualification Round 1

CF 345A - Expecting Trouble

Surprise Language Round 5

CF 172C - Bus

CF 290F - Greedy Petya

CF 159E - Zebra Tower

CF 158A - Next Round

CF 409H - A + B Strikes Back

CF 153C - Caesar Cipher

CF 345F - Superstitions Inspection

CF 291E - Tree-String Problem

Coder-Strike 2014 - Qualification Round

CF 290D - Orange

CF 171B - Star

CF 188E - HQ9+

CF 172A - Phone Code

CF 171C - A Piece of Cake

CF 158B - Taxi

CF 188B - A + Reverse B

April Fools Day Contest 2014

CF 345D - Chain Letter

Croc Champ 2013 - Qualification Round

CF 409A - The Great Game