Educational Codeforces Round 18 D. Paths in a Complete Binary Tree

Codeforces Round 408 (Div. 2) C. Bank Hacking

Educational Codeforces Round 20 C. Maximal GCD

Educational Codeforces Round 20 D. Magazine Ad

Educational Codeforces Round 21 D. Array Division

Educational Codeforces Round 24 E. Card Game Again

Codeforces Round 416 (Div. 2) C. Vladik and Memorable Trip

2818. Apply Operations to Maximize Score

You are given an array nums of n positive integers and an integer k.

Initially, you start with a score of 1. You have to maximize your score by applying the following operation at most k times:

• Choose any non-empty subarray nums[l, ..., r] that you haven’t chosen previously.
• Choose an element x of nums[l, ..., r] with the highest prime score. If multiple such elements exist, choose the one with the smallest index.
• Multiply your score by x.

Here, nums[l, ..., r] denotes the subarray of nums starting at index l and ending at the index r, both ends being inclusive.

The prime score of an integer x is equal to the number of distinct prime factors of x. For example, the prime score of 300 is 3 since 300 = 2 * 2 * 3 * 5 * 5.

Return the maximum possible score after applying at most k operations.

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

2817. Minimum Absolute Difference Between Elements With Constraint

You are given a 0-indexed integer array nums and an integer x.

Find the minimum absolute difference between two elements in the array that are at least x indices apart.

In other words, find two indices i and j such that abs(i - j) >= x and abs(nums[i] - nums[j]) is minimized.

Return an integer denoting the minimum absolute difference between two elements that are at least x indices apart.

2816. Double a Number Represented as a Linked List

You are given the head of a non-empty linked list representing a non-negative integer without leading zeroes.

Return the head of the linked list after doubling it.