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[] arr = new int[5];
for (int i = 0; i < 5; i ++) {
arr[i] = 1;
}
for (int i = 2; i <= n; i ++) {
for (int j = 0; j < 5; j ++) {
for (int k = j + 1; k < 5; k ++) {
arr[j] += arr[k];
}
}
}
int res = 0;
for (int i = 0; i < 5; i ++) {
res += arr[i];
}
return res;
}
}