【大数问题】 HDOJ 4927 Series 1

大数+组合数。。。

import java.util.Scanner;import java.math.BigInteger;import java.math.BigDecimal;public class Main{public static void main(String[] args){Scanner scanner = new Scanner(System.in);BigInteger f[] = new BigInteger[3005];BigInteger num[] = new BigInteger[3005];BigInteger ans, tmp;int t = scanner.nextInt();while((t--) != 0) {int n = scanner.nextInt();f[0] = BigInteger.ONE;for(int i = 1; i < n; i++) {tmp = BigInteger.valueOf(n-i);f[i] = f[i-1].multiply(tmp);tmp = BigInteger.valueOf(i);f[i] = f[i].divide(tmp);}ans = BigInteger.ZERO;for(int i = 0; i < n; i++) num[i] = scanner.nextBigInteger();int flag = 0;for(int i = n-1; i >= 0; i--) {if(flag == 0) {ans = ans.add(f[i].multiply(num[i]));flag = 1;}else {ans = ans.subtract(f[i].multiply(num[i]));flag = 0;}}System.out.println(ans.toString());}}}