Euler P20.java

public void p20() {
	String v = fact(100);
	int r = 0;

	for (int i = 0; i < v.length(); i++) {
		r += (int)Character.digit(v.charAt(i), 10);
	}

	System.out.println(r);
}

public String fact(long n) {
	if (n  0) {
		for (int i = 0; i < dif; i++) {
			b = "0" + b;
		}
	} else if (dif < 0) {
		for (int i = 0; i > dif; i--) {
			a = "0" + a;
		}
	}

	int carry = 0;
	String result = "";

	for (int i = len - 1; i >= 0; i--) {
		int digit = (int)Character.digit(a.charAt(i), 10) 
                          + (int)Character.digit(b.charAt(i), 10) 
                          + carry;

		if (digit > 9) {
			carry = 1;
			digit -= 10;
		} else {
			carry = 0;
		}

		result = digit + result;
	}

	if (carry == 1) {
		result = carry + result;
	}

	return result;
}