Factorial

/**
    * @param n - max is 20
    * @return The factorial of the number
*/
public static long stackFactorial(int n) {
    if (n == 1 || n == 0)
        return 1;
    else
        return stackFactorial(n - 1) * n;
}

/**
    * @param n - max is 20
    * @return The factorial of the number
*/
public static long loopFactorial(int n) {
    long r = 1;
    for (long i = 1; i <= n; i++) {
        r *= i;
    }
    return r;
}