阶乘运算，随便写一个1000!，结论大家自己去总结吧！

================Python版================
print reduce(lambda x,y:x*y, range(1, 1001))

================Java版================
import java.io.*;
import java.math.*;
public class Main
{
    public static BigDecimal fact(int num)
    {
        BigDecimal sum = new BigDecimal(1.0);
        int i;
        BigDecimal a;
        for(i = 1; i <= num; i++)
        {
            a = new BigDecimal(i);
            sum =sum.multiply(a);
        }
        return sum;
    }
    public static void main(String args[])
    {
       System.out.println(fact(1000));
    }
}