hdu 1143 Tri Tiling

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Tri Tiling

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)

Total Submission(s): 2112 Accepted Submission(s): 1206

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

2812-1

Sample Output

31532131

总结：

代码比较简单易懂，但是我们要注重递推过程，根据自己动手动脑推出递推公式。

递推：

<span style="font-size:18px;">#include<stdio.h>int main (){ int n,i; int a[40]; while(~scanf("%d",&n)&&n!=-1) {  a[0]=1; // 为什么是1???  a[1]=0;  a[2]=3;  a[3]=0;  a[4]=11;  for(i=5;i<=31;i++)  {   if(i%2==0)   a[i]=a[i-2]*4-a[i-4];   else    a[i]=0;  }  printf("%d\n",a[n]); }}</span>

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