1641. Count Sorted Vowel Strings

https://leetcode.com/problems/count-sorted-vowel-strings

Description

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:

• 1 <= n <= 50

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