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:

• 1 <= n <= 50

Solution:

class Solution {
    public int countVowelStrings(int n) {
        int a=1,e=1,i=1,o=1,u=1;
        while(--n>0)
        {
            u=u;
            o+=u;
            i+=o;
            e+=i;
            a+=e;
        }
        
        return a+e+i+o+u;
    }
}