hdu 1130 How Many Trees?(二叉树节点的Catalan数)

import java.util.*;
import java.math.BigInteger;
public class Main {

public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner In=new Scanner(System.in);
BigInteger []b=new BigInteger[110];
b[1]=BigInteger.ONE;
int i,a;
while(In.hasNext()){
a=In.nextInt();
for(i=2;i<=a;i++){
int t=4*i-2;
b[i]=b[i-1].multiply(BigInteger.valueOf(t)).divide(BigInteger.valueOf(i+1));
}
System.out.println(b[a].toString());
}
}

}