hdu 1261(组合数+java大数)

设多重集的个数n = n1 + n2 + ... + nk;
则该多重集的排列个数为：n!/(n1!n2!...nk!).

//组合数+java大数
import java.util.Scanner;
import java.math.BigInteger;

public class hdu1261
{
	public static void main(String args[]) 
	{
		Scanner cin = new Scanner(System.in);
		BigInteger f1, f2;
		int []s = new int[26];
		int n, sum;
		n = cin.nextInt();
		while (n != 0)
		{
			sum = 0;
			for (int i=0; i<n; ++i)
			{
				s[i] = cin.nextInt();
				sum += s[i];
			}
			f1 = new BigInteger("1");
			for (int i=1; i<=sum; ++i)
			{
				f1 = f1.multiply(BigInteger.valueOf(i));
			}
			f2 = new BigInteger("1");
			for (int i=0; i<n; ++i)
			{
				for (int j=1; j<=s[i]; ++j)
				{
					f2 = f2.multiply(BigInteger.valueOf(j));
				}
			}
			System.out.println(""+f1.divide(f2));
			n = cin.nextInt();
		}
	}
}