Project Euler NO20

算出100！的各位之和。

import java.math.BigInteger;


public class Problem20
{
	public static void main(String[] args)
	{
		long start = System.currentTimeMillis();
		System.out.print("answer:  ");
		
		bigint();
		
		long end = System.currentTimeMillis();
		System.out.print("time:  ");
		System.out.println(end - start);
	}
	
	static void bigint()
	{
		BigInteger a = BigInteger.valueOf(1);
		for (int i = 2; i <= 100; i++)
		{
			a = a.multiply(BigInteger.valueOf(i));
		}
		
		int sum = 0;
		for (int i = 0; i < (a+"").length(); i++)
		{
			sum += Integer.parseInt((a+"").substring(i,i+1));
		}
		
		System.out.println(sum);
	}
}

answer:  648
time:  98