hdu 1023 Train Problem II (卡特兰数)

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http://acm.hdu.edu.cn/showproblem.php?pid=1023

h(n)=(4*n-2)*h(n-1)/(n+1);

/*2011-9-7author:BearFly1990*/package acm.hdu.tests;import java.io.BufferedInputStream;import java.math.BigInteger;import java.util.Scanner;public class HDU_1023{    public static void main(String[] args)    {        BigInteger[] ans=new BigInteger[102];        int i;        Scanner cin = new Scanner(new BufferedInputStream(System.in));        ans[0]=BigInteger.valueOf(1);        ans[1]=BigInteger.valueOf(1);        for(i=2;i<102;i++)        {            ans[i]=(((BigInteger.valueOf(4).multiply(BigInteger.valueOf(i)))                    .subtract(BigInteger.valueOf(2)))                    .multiply(ans[i-1]))                    .divide(BigInteger.valueOf(i)                    .add(BigInteger.valueOf(1)));        }        while(cin.hasNext())        {            i=cin.nextInt();            System.out.println(ans[i]);        }    }}