2842. Count K-Subsequences of a String With Maximum Beauty

You are given a string s and an integer k. A k-subsequence is a subsequence of s, having length k, and all its characters are unique, i.e., every character occurs once. Let f(c) denote the number of times the character c occurs in s. The beauty of a k-subsequence is the sum of f(c) for every character c in the k-subsequence. For example, consider s = "abbbdd" and k = 2: - f('a') = 1, f('b') =