字串数 排练组合(阶乘) java秒

 1 import java.math.*;
 2 import java.util.*;
 3 import java.io.*;
 4 import java.text.*;
 5 
 6 public class Main
 7 {
 8     
 9     public static void main(String[] args)
10     {
11         Scanner cin=new Scanner(new BufferedInputStream(System.in));
12         while(cin.hasNext())
13         {
14             int n=cin.nextInt();
15             if(n==0)
16                 break;
17             int[]  a=new int[n];
18             int sum=0;
19             for(int i=0;i<n;i++)
20             {
21                 a[i]=cin.nextInt();
22                 sum+=a[i];
23             }
24             BigInteger ans=fact(sum);
25             for(int i=0;i<n;i++)
26                 ans=ans.divide(fact(a[i]) );
27             System.out.println(ans);
28         }
29         cin.close();
30     }
31     public static BigInteger fact(int n)
32     {
33         BigInteger res=BigInteger.ONE;
34         for(int i=2;i<=n;i++)
35             res=res.multiply(BigInteger.valueOf(i));
36         return res;
37     }
38 }