http://acm.hdu.edu.cn/showproblem.php?pid=1996

递推

View Code
#include <iostream>
#include <string>
using namespace std;
int main()
{
    int t;
    __int64 dp[30]={0,3};
    for(int i=2;i<30;i++)
        dp[i]=dp[i-1]*3;
    scanf("%d",&t);
    while(t--)
    {
        int n;
        scanf("%d",&n);
        printf("%I64d\n",dp[n]);
    }
    return 0;
}