Project Euler - Problem 20

euler.java

package euler;

import java.math.BigInteger;

public class BigFact {
	
	public static void main(String[] args) {
		System.out.println(sum(f(BigInteger.valueOf(100)).toString()));
	}
	
	public static BigInteger f(BigInteger n) {
		if (n.equals(BigInteger.ZERO)) return BigInteger.ONE;
		else return n.multiply(f(n.subtract(BigInteger.ONE)));
	}
	public static int sum(String s) {
		int sum = 0;
		for (int i = 0; i < s.length(); i++) {
			sum += s.charAt(i) - 48;
		}
		return sum;
	}
}