HDU 2047 阿牛的EOF牛肉串

http://acm.hdu.edu.cn/showproblem.php?pid=2047

也是倒推，a[i] = 2*(a[i-1]+a[i-2])

#include<iostream>
#include<cmath>
#include<algorithm>
using namespace std;


int main()
{
          int n;
          while(cin>>n && n)
          {
                    long long a[50];
                    a[1] = 3;
                    a[2] = 8;
                    for(int i = 3;i<=n;i++)
                              a[i] = 2*(a[i-1]+a[i-2]);
                    cout<<a[n]<<endl;
          }

}