学步园

Catalan数，组合数学书上有公式。

import java.math.*;  
import java.io.*;  
import java.util.*;  
public class Main {  
    public static void main(String [] args){  
        Scanner cin = new Scanner(System.in);  
        BigInteger a[] = new BigInteger[101];  
        a[0] = BigInteger.ONE;  
        for(int i=1; i<=100; ++i){  
            a[i] = a[i-1].multiply(BigInteger.valueOf(4*i-2)).divide(BigInteger.valueOf(i+1));  
        }  
        while(cin.hasNext()){  
        	int n= cin.nextInt();
        	if(n==-1) break;
            System.out.println(a[n]);  
        }  
    }  
}