Series 1 java秒组合数

 1 import java.math.*;
 2 import java.util.*;
 3 import java.io.*;
 4 import java.text.*;
 5 
 6 public class Main
 7 {
 8     static int MS=3005;
 9     public static void main(String[] args)
10     {
11         Scanner cin=new Scanner(new BufferedInputStream(System.in));
12         int[] a=new int[MS];
13         int T,n;
14         T=cin.nextInt();
15         while(T-->0)
16         {
17             n=cin.nextInt();
18             for(int i=0;i<n;i++)
19                 a[i]=cin.nextInt();
20             BigInteger ans=BigInteger.valueOf(a[n-1]);
21             BigInteger res=BigInteger.ONE;
22             BigInteger flag=BigInteger.valueOf(-1);
23             BigInteger t=BigInteger.ONE;
24             n=n-1;
25             for(int i=1,j=n;i<=n;i++,j--)
26             {
27                 res=res.multiply(BigInteger.valueOf(j)).divide(BigInteger.valueOf(i));
28                 t=res.multiply(flag).multiply(BigInteger.valueOf(a[j-1]));
29                 flag=flag.multiply(BigInteger.valueOf(-1));
30                 ans=ans.add(t);
31             }
32             System.out.println(ans);
33         }
34         cin.close();
35     }
36 }