{leetcode}/problems/count-sorted-vowel-strings/[LeetCode - 1641. 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.
Example 1:
Input: n = 1
Output: 5
Explanation: The 5 sorted strings that consist of vowels only are ["a","e","i","o","u"].
Example 2:
Input: n = 2 Output: 15 Explanation: The 15 sorted strings that consist of vowels only are ["aa","ae","ai","ao","au","ee","ei","eo","eu","ii","io","iu","oo","ou","uu"]. Note that "ea" is not a valid string since 'e' comes after 'a' in the alphabet.
Example 3:
Input: n = 33 Output: 66045
Constraints:
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1 ⇐ n ⇐ 50