hdu4165(卡特兰数)

Pills

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 764    Accepted Submission(s): 500

Problem Description

Aunt Lizzie takes half a pill of a certain medicine every day. She starts with a bottle that contains N pills.

On the first day, she removes a random pill, breaks it in two halves, takes one half and puts the other half back into the bottle.

On subsequent days, she removes a random piece (which can be either a whole pill or half a pill) from the bottle. If it is half a pill, she takes it. If it is a whole pill, she takes one half and puts the other half back into the bottle.

In how many ways can she empty the bottle? We represent the sequence of pills removed from the bottle in the course of 2N days as a string, where the i-th character is W if a whole pill was chosen on the i-th day, and H if a half pill was chosen (0 <= i < 2N). How many different valid strings are there that empty the bottle?

 

Input

The input will contain data for at most 1000 problem instances. For each problem instance there will be one line of input: a positive integer N <= 30, the number of pills initially in the bottle. End of input will be indicated by 0.

 

Output

For each problem instance, the output will be a single number, displayed at the beginning of a new line. It will be the number of different ways the bottle can be emptied.

 

Sample Input

  
  

   
   6
1
4
2
3
30
0
  
  

 

Sample Output

  
  

   
   132
1
14
2
5
3814986502092304
  
  

 

Source

The 2011 Rocky Mountain Regional Contest

 

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import java.math.BigInteger;
import java.util.Scanner;


public class hdu4165 {
	
	static BigInteger []f=new BigInteger[110];
	static void catlan()
	{	
		f[0]=new BigInteger("1");
		f[1]=new BigInteger("1");
		for(int i=2;i<31;i++)
		{
			f[i]=new BigInteger("0");
			for(int j=0;j<i;j++)
			{
				f[i]=f[i].add( f[j].multiply(f[i-j-1]) );
			}
		}
	}
	
	
	public static void main(String[] str)
	{
		Scanner input=new Scanner(System.in);
		catlan();
		int i;
		while(input.hasNext())
		{
			i=input.nextInt();
			if(0==i)break;
		   System.out.println(f[i]);
		}
	}
}