factorial

f.java

public class Factorial {
    public static BigInteger factorial(int n) {
        BigInteger t = new BigInteger("1");
        
        if (n == 0 || n == 1) return t;
        
        for (int i = 2; i <= n; i++)
            t = t.multiply(new BigInteger(Integer.toString(i)));
        
        return t;
    }