1641. Count Sorted Vowel Strings | LeetCode Solution

 1641. Count Sorted Vowel Strings | LeetCode Solution

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 

class Solution {

public:

    int countVowelStrings(int n) {

        vector<int>dp(5,1);

        int ans=0;

        while(--n){

            for(int i=3; i>=0; i--){

                dp[i]+=dp[i+1];

            }

        }

        for(auto x:dp)ans+=x;

        return ans;

    }

};