HDU1143：Tri Tiling

Problem Description

In how many ways can you tile a 3xn rectangle with 2x1 dominoes? Here is a sample tiling of a 3x12 rectangle.

 

Input

Input consists of several test cases followed by a line containing -1. Each test case is a line containing an integer 0 ≤ n ≤ 30.  

 

Output

For each test case, output one integer number giving the number of possible tilings.  

 

Sample Input

   
   
   
   

    
    
    
    2
8
12
-1
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    3
153
2131
   
   
   
   

 

#include <stdio.h>

int f[50] = {0};
int i,n;

int main()
{
    f[0] = 1;
    f[2] = 3;
    for(i = 4;i<=30;i+=2)
    {
        f[i] = f[i-2]*4-f[i-4];
    }
    while(~scanf("%d",&n),n>=0)
    {
        printf("%d\n",f[n]);
    }


    return 0;
}