Codeforces Round 223 (Div. 1) C. Sereja and Brackets

2264. Largest 3-Same-Digit Number in String

You are given a string num representing a large integer. An integer is good if it meets the following conditions:

• It is a substring of num with length 3.
• It consists of only one unique digit.

Return the maximum good integer as a string or an empty string "" if no such integer exists.

Note:

• A substring is a contiguous sequence of characters within a string.
• There may be leading zeroes in num or a good integer.

Codeforces Round 224 (Div. 2) B. Number Busters

2954. Count the Number of Infection Sequences

You are given an integer n and a 0-indexed integer array sick which is sorted in increasing order.

There are n children standing in a queue with positions 0 to n - 1 assigned to them. The array sick contains the positions of the children who are infected with an infectious disease. An infected child at position i can spread the disease to either of its immediate neighboring children at positions i - 1 and i + 1 if they exist and are currently not infected. At most one child who was previously not infected can get infected with the disease in one second.

It can be shown that after a finite number of seconds, all the children in the queue will get infected with the disease. An infection sequence is the sequential order of positions in which all of the non-infected children get infected with the disease. Return the total number of possible infection sequences.

Since the answer may be large, return it modulo 109 + 7.

Note that an infection sequence does not contain positions of children who were already infected with the disease in the beginning.

2953. Count Complete Substrings

You are given a string word and an integer k.

A substring s of word is complete if:

• Each character in s occurs exactly k times.
• The difference between two adjacent characters is at most 2. That is, for any two adjacent characters c1 and c2 in s, the absolute difference in their positions in the alphabet is at most 2.

Return the number of complete substrings of word.

A substring is a non-empty contiguous sequence of characters in a string.

2952. Minimum Number of Coins to be Added

You are given a 0-indexed integer array coins, representing the values of the coins available, and an integer target.

An integer x is obtainable if there exists a subsequence of coins that sums to x.

Return the minimum number of coins of any value that need to be added to the array so that every integer in the range [1, target] is obtainable.

A subsequence of an array is a new non-empty array that is formed from the original array by deleting some (possibly none) of the elements without disturbing the relative positions of the remaining elements.

2951. Find the Peaks

You are given a 0-indexed array mountain. Your task is to find all the peaks in the mountain array.

Return an array that consists of indices of peaks in the given array in any order.

Notes:

• A peak is defined as an element that is strictly greater than its neighboring elements.
• The first and last elements of the array are not a peak.

Codeforces Round 225 (Div. 1) C. Propagating tree

Testing Round 9 C. Diverse Substrings

Codeforces Round 228 (Div. 1) C. Fox and Card Game