Codeforces Round 861 (Div. 2)

Solutions for Codeforces Round 861 (Div. 2) (contest 1808). 3/6 problems verified against sample I/O. Difficulty range: 900-2800.

6 items

Codeforces Round 861 (Div. 2)

Type: Div. 2 | Problems: 6 | Verified: 3/6 | Rating range: 900-2800 | Time: 13m 55s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Lucky Numbers	900	brute-force, implementation	1m 57s	✗
B	Playing in a Casino	1200	math, sortings	1m 24s	✓
C	Unlucky Numbers	1900	brute-force, dp, greedy	4m 5s	✗
D	Petya, Petya, Petr, and Palindromes	2100	binary-search, brute-force, data-structures	2m 17s	✓
E1	Minibuses on Venus (easy version)	2200	combinatorics, divide-and-conquer, dp	1m 39s	✗
E3	Minibuses on Venus (hard version)	2800	brute-force, combinatorics, dp	2m 33s	✓

Practice › Codeforces Solutions › Codeforces Round 861 (Div. 2) ›

CF 1808E3 - Minibuses on Venus (hard version)

A ticket is a sequence of n digits in base k, so every position contains a value from 0 to k - 1. Let the total digit sum modulo k be $$S = a1 + a2 + dots + an pmod k.$$ A ticket is lucky if there exists some position whose digit equals the sum of all remaining digits modulo k.

Practice › Codeforces Solutions › Codeforces Round 861 (Div. 2) ›

CF 1808C - Unlucky Numbers

You’re hitting a classic off-by-one / misunderstanding of what “sample input” means in these later prompts.

Practice › Codeforces Solutions › Codeforces Round 861 (Div. 2) ›

CF 1808D - Petya, Petya, Petr, and Palindromes

For every subarray of odd length k, we want to know how many element replacements are needed to turn that subarray into a palindrome. The answer is the sum of those values over all length-k subarrays.

Practice › Codeforces Solutions › Codeforces Round 861 (Div. 2) ›

CF 1808E1 - Minibuses on Venus (easy version)

We are asked to count tickets with a specific property in a non-decimal numeral system. Each ticket is an array of length n with elements from 0 to k-1. A ticket is "lucky" if one of its digits equals the sum of all other digits modulo k.

Practice › Codeforces Solutions › Codeforces Round 861 (Div. 2) ›

CF 1808A - Lucky Numbers

We are asked to find the "luckiest" number within a given range of integers. Luckiness of a number is defined as the difference between its largest and smallest digit. For example, the number 142857 has digits ranging from 1 to 8, so its luckiness is 8 - 1 = 7.

Practice › Codeforces Solutions › Codeforces Round 861 (Div. 2) ›

CF 1808B - Playing in a Casino

Each player receives a card containing m integers. For every pair of players, the amount won in their game is the sum of absolute differences between the corresponding positions on their cards. If player i has card values c[i][1...m] and player j has card values c[j][1...