HDU 1130

题目大意

给定节点数，求通过这么多个节点能得到的二叉树的组成方式

用卡特兰数解决

f[n] = (4*n-2) * f[n-1] / (n+1);

递归不断解决

 1 /**
 2  * @(#)Main.java
 3  *
 4  *
 5  * @author 
 6  * @version 1.00 2014/12/29
 7  */
 8 
 9 import java.util.Scanner;
10 import java.math.*;
11 
12 public class Main {
13 
14     
15     public static void main(String [] args){
16         int n;
17         Scanner input = new Scanner(System.in);
18 
19         while(input.hasNext()){
20             n = input.nextInt();
21             BigInteger cur = BigInteger.valueOf(1);
22             for(int i = 2 ; i<=n ; i++){
23                 int t1 = 4*i - 2;
24                 int t2 = i+1;
25                 BigInteger tmp1 = BigInteger.valueOf(t1);
26                 cur = cur.multiply(tmp1);
27                 BigInteger tmp2 = BigInteger.valueOf(t2);
28                 cur = cur.divide(tmp2);
29             }
30             System.out.println(cur);
31         }
32     }
33     
34     
35 }