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();

		}

	}

}