裸卡兰特数

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1130

卡兰特数：令h(1)=1,h(0)=1，catalan数满足递归式：                  //h(n)=(4*n-2)/(n+1)*h(n-1);

JAVA代码

import java.math.BigInteger;
import java.util.*;
public class Main{
	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		BigInteger[] arr = new BigInteger[1100];
		arr[0] = BigInteger.ONE;
		arr[1] = BigInteger.ONE;
		BigInteger four = BigInteger.valueOf(4);
		BigInteger two = BigInteger.valueOf(2);
		BigInteger one = BigInteger.valueOf(1);
		for(int i=2;i<1001;i++){
			arr[i] = arr[i-1].multiply(four.multiply(BigInteger.valueOf(i)).subtract(two)).divide(BigInteger.valueOf(i).add(one));
		}
		int pos;
		while(in.hasNext()){
			pos = in.nextInt();
			System.out.println(arr[pos]);
		}
	}
}