uva 580 Critical Mass(递推)

#include<stdio.h>
#include<algorithm>
#include<string.h>
#include<iostream>
using namespace std;
typedef unsigned long long ull;

int main()
{
    int i,j,n;
    ull f[35],a[35],g[35];
    a[0]=1;
    for(i=1;i<=30;i++)
    {
        a[i]=a[i-1]*2;
    }
    f[0]=f[1]=f[2]=0;
    g[0]=1;g[1]=2;g[2]=4;
    for(i=3;i<=30;i++)
    {
        f[i]=a[i-3];
        for(j=2;j<=i-2;j++)
        {
            f[i]+=g[j-2]*a[i-j-2];
        }
        g[i]=a[i]-f[i];
    }
    while(~scanf("%d",&n)&&n)
    {
        cout<<f[n]<<endl;
    }
    return 0;
}