递推 HDU 1143

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<math.h>

using namespace std;

#define MAXN 105
long long  z[45];

int main()
{
    int n;
    z[0]=1;
    z[1]=0;
    z[2]=3;
    for(int i=3;i<=30;i++)
    {
        if(i%2==0)
            z[i]=4*z[i-2]-z[i-4];
        else
            z[i]=0;
    }

    while(scanf("%d",&n)!=EOF)
    {
        if(n==-1)
            break;
        printf("%lld\n",z[n]);
    }
    return 0;
}