Method dfs

java/1220-count-vowels-permutation.java:113–140

(char c, int n, int l)

    }

    private int dfs(char c, int n, int l){
        if(l == n)
            return 1;
        
        String key = c + "_" + l;
        if (memo.containsKey(key)) return memo.get(key);

        long res = 0;
        if (c == 'a') {
            res = dfs('e', n, l + 1);
        } else if (c == 'e') {
            res = (res + dfs('a', n, l + 1)) % MOD;
            res = (res + dfs('i', n, l + 1)) % MOD;
        } else if (c == 'i') {
            res = (res + dfs('a', n, l + 1)) % MOD;
            res = (res + dfs('e', n, l + 1)) % MOD;
            res = (res + dfs('o', n, l + 1)) % MOD;
            res = (res + dfs('u', n, l + 1)) % MOD;
        } else if (c == 'o') {
            res = (res + dfs('i', n, l + 1)) % MOD;
            res = (res + dfs('u', n, l + 1)) % MOD;
        } else {
            res = dfs('a', n, l + 1);
        }

        memo.put(key, (int)(res % MOD));
        return (int)(res % MOD);    
    }
}