poj 2663 Tri Tiling

Tri Tiling

Time Limit: 1000MS Memory Limit: 65536KTotal Submissions: 7887 Accepted: 4134

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

题解：a[i]=4*a[i-2]-a[i-4];  

#include <iostream>using namespace std;int main(){long long n,a[50];a[0]=1;a[2]=3; for(int i=4;i<=30;i+=2)  a[i]=4*a[i-2]-a[i-4];  while (cin>>n&&n!=-1){if (n%2)cout<<0<<endl;elsecout<<a[n]<<endl;}return 0;}