source: https://leetcode.com/problems/count-sorted-vowel-strings/description/ Count Sorted Vowel Strings Given an integer n, return the number of strings of length n that consist only of vowels (a, e, i, o, u) and are lexicographically sorted. A string s is lexicographically sorted if for all valid i, s[i] is the same as or comes before s[i+1] in the alphabet. ...