HDU 4927 Series 1 ( 组合+高精度)

 1 import java.io.*;
 2 import java.math.*;
 3 import java.util.*;
 4 public class Main {            
 5     
 6     static BigInteger coe[][] = new BigInteger [3010][3010];
 7     public static void main(String[] args) throws IOException{
 8         Scanner cin = new Scanner(System.in);
 9         BigInteger []a = new BigInteger[3010];  
10         BigInteger []c = new BigInteger[3010]; 
11         int T;
12         T = cin.nextInt();
13         while(T-- > 0){
14             int n;
15             n = cin.nextInt();
16             for(int i = 1; i <= n; ++i){
17                 a[i] = cin.nextBigInteger();
18             }
19             BigInteger ans = BigInteger.ZERO;
20             c[0] = BigInteger.ONE;
21             ans = ans.add(c[0].multiply(a[n]));
22             int t = -1;
23             for(int i = 1; i < n; ++i){
24                 BigInteger t1 = BigInteger.valueOf(n).subtract(BigInteger.valueOf(i));  
25                 BigInteger t2 = BigInteger.valueOf(i);
26                 c[i] = c[i-1].multiply(t1).divide(t2); 
27                 ans = ans.add(c[i].multiply(a[n-i]).multiply(BigInteger.valueOf(t)));
28                 t *= -1; 
29             }
30             System.out.println(ans);
31         }
32         
33     }
34 }