hdu.2047
没什么好讲的,多写几项规律就出来了:f(n)=2*(f(n-1)+f(n-2))
接下来就是递归加打表
#include<iostream>
using namespace std;
#define N 40
long long a[40] = { 0,3,8,22, };
long long sum(int n)
{
if (n == 1)
return 3;
if (n == 2)
return 8;
if(a[n]==0)
a[n]= (sum(n - 1) + sum(n - 2))*2;
return a[n];
}
int main()
{
int n;
while (cin>>n)
{
cout << sum(n) << endl;
}
return 0;
}