Educational Codeforces Round 75 (Rated for Div. 2) D. Salary Changing

Educational Codeforces Round 77 (Rated for Div. 2) D. A Game with Traps

2791. Count Paths That Can Form a Palindrome in a Tree

You are given a tree (i.e. a connected, undirected graph that has no cycles) rooted at node 0 consisting of n nodes numbered from 0 to n - 1. The tree is represented by a 0-indexed array parent of size n, where parent[i] is the parent of node i. Since node 0 is the root, parent[0] == -1.

You are also given a string s of length n, where s[i] is the character assigned to the edge between i and parent[i]. s[0] can be ignored.

Return the number of pairs of nodes (u, v) such that u < v and the characters assigned to edges on the path from u to v can be rearranged to form a palindrome.

A string is a palindrome when it reads the same backwards as forwards.

2790. Maximum Number of Groups With Increasing Length

You are given a 0-indexed array usageLimits of length n.

Your task is to create groups using numbers from 0 to n - 1, ensuring that each number, i, is used no more than usageLimits[i] times in total across all groups. You must also satisfy the following conditions:

• Each group must consist of distinct numbers, meaning that no duplicate numbers are allowed within a single group.
• Each group (except the first one) must have a length strictly greater than the previous group.

Return an integer denoting the maximum number of groups you can create while satisfying these conditions.

2789. Largest Element in an Array after Merge Operations

You are given a 0-indexed array nums consisting of positive integers.

You can do the following operation on the array any number of times:

• Choose an integer i such that 0 <= i < nums.length - 1 and nums[i] <= nums[i + 1]. Replace the element nums[i + 1] with nums[i] + nums[i + 1] and delete the element nums[i] from the array.

Return the value of the largest element that you can possibly obtain in the final array.

2788. Split Strings by Separator

Given an array of strings words and a character separator, split each string in words by separator.

Return an array of strings containing the new strings formed after the splits, excluding empty strings.

Notes

• separator is used to determine where the split should occur, but it is not included as part of the resulting strings.
• A split may result in more than two strings.
• The resulting strings must maintain the same order as they were initially given.

Codeforces Round 604 (Div. 1) B. Beautiful Sequence

Good Bye 2019 D. Strange Device

Codeforces Round 605 (Div. 3) E. Nearest Opposite Parity

2787. Ways to Express an Integer as Sum of Powers

Given two positive integers n and x.

Return the number of ways n can be expressed as the sum of the xth power of unique positive integers, in other words, the number of sets of unique integers [n1, n2, ..., nk] where n = n1x + n2x + ... + nkx.

Since the result can be very large, return it modulo 109 + 7.

For example, if n = 160 and x = 3, one way to express n is n = 23 + 33 + 53.