HDU 1016 Prime Ring Problem

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int n,v[25],a[25];
int ssb[100],zj[100],pn;
void f()
{
    int i,j;
    zj[0]=1;
    zj[1]=1;
    pn=0;
    for (i=2;i<=100;i++)
    {
        if (zj[i]==0) ssb[pn++]=i;
        for (j=0;j<pn;j++)
        {
            if (i*ssb[j]>100) break;
            zj[i*ssb[j]]=1;
            if (i%ssb[j]==0) break;
        }
    }
}
void dfs(int x,int k)
{
    int i,j;
    for (i=2;i<=n;i++)
    {
        if (!v[i]&&zj[i+x]==0)
        {
            v[i]=1;
            a[k+1]=i;
            if (k+1==n)
            {
                if (zj[1+a[n]]==0){
                for (j=1;j<n;j++) printf("%d ",a[j]);
                printf("%d\n",a[n]);}
            }
            dfs(i,k+1);
            v[i]=0;
        }
    }
}
int main()
{
    int cut=1;
    a[1]=1;
    memset(zj,0,sizeof(zj));
    f();
    while (~scanf("%d",&n))
    {
        printf("Case %d:\n",cut);
        cut++;
        memset(v,0,sizeof(v));
        dfs(1,1);
        printf("\n");
    }
    return 0;
}