SGU247(排列组合与大数运算)

题目：Difficult Choice

 

题目分析以及公式推导：

 

import java.io.*;import java.util.*;import java.math.BigInteger;public class Solution{ public static BigInteger fac[]=new BigInteger[2013]; public static void main(String[] args) {  init();  Scanner cin = new Scanner(System.in);  int t = cin.nextInt();  while(t--!=0)  {   int p=cin.nextInt();   BigInteger ans=fac[2*p];   BigInteger temp=fac[p];   ans=ans.divide(temp);   ans=ans.divide(temp);   ans=ans.subtract(BigInteger.valueOf(2));   ans=ans.divide(BigInteger.valueOf(p));   ans=ans.add(BigInteger.valueOf(2));   System.out.println(ans);  } } public static void init() {  for(int i=1;i<2012;i++)  fac[i]=BigInteger.ONE;  for(int i=2;i<2012;i++)  fac[i]=fac[i-1].multiply(BigInteger.valueOf(i)); }}