1220. Count Vowels Permutation.md

Code for ' 1220. Count Vowels Permutation ' (Java)

class Solution {
    public int countVowelPermutation(int n) {
        if (n == 0)
            return 0;

        // dp initialization
        // f[i][j], string length == i, ending with vowel[j]
        long[][] f = new long[n][5];

        for (int j = 0; j < 5; j++)
            f[0][j] = 1;

        int a = 0, e = 1, i = 2, o = 3, u = 4;
        int mod = (int) Math.pow(10, 9) + 7;

        for (int r = 1; r < n; r++) {
            f[r][a] = (f[r - 1][e] + f[r - 1][i] + f[r - 1][u]) % mod;
            f[r][e] = (f[r - 1][a] + f[r - 1][i]) % mod;
            f[r][i] = (f[r - 1][e] + f[r - 1][o]) % mod;
            f[r][o] = (f[r - 1][i]) % mod;
            f[r][u] = (f[r - 1][i] + f[r - 1][o]) % mod;
        }

        long res = 0;
        for (int j = 0; j < 5; j++)
            res = (res + f[n - 1][j]) % mod;

        return (int) res;
    }
}