hdu 1261 字串数

指数型母函数应用！！！

import java.math.*; import java.util.*;

public class Main {
    public static int []a;
    public static void main(String arg[]){ BigInteger [] p =new BigInteger[313];
        p[1]=BigInteger.ONE;
        int i;
        for(i=2;i<=312;i++){
            p[i] = p[i-1].multiply(BigInteger.valueOf(i));
        }
        Scanner cin = new Scanner(System.in);
        a =new int[27];
        int t,sum;
        while (true){
            t = cin.nextInt();
            if(t==0) break;
            sum=0;
            for(i=0;i<t;i++){
                a[i]=cin.nextInt(); sum+=a[i];
            }
            BigInteger ans = p[sum];
            for(i=0;i<t;i++){ ans=ans.divide(p[a[i]]);
            }
            System.out.println(ans.toString());
        }
    }
}