Prime Ring Problem hdu 1016 dfs

#include<iostream>//2365548 2010-04-21 14:16:05 Accepted 1016 500MS 300K 1160 B C++ 悔惜晟
#include<cstring>
using namespace std;

bool hash[40];
bool hash1[25];
int num[25];
int n;

void dfs(int count)
{
 int j;
 if(count == n)
 {
  if(hash[ num[1] + num[n] ])
  {
   for( j = 1; j <= n; j++)
   if(j != n) 
    cout<<num[j]<<" ";
   else
    cout<<num[j];
    cout<<endl;
  }
 }
 //if(!hash[num[count]])
  //return ;
 else
 for(j = 2; j <= n; j++)
  if(hash[num[count ] + j] && !hash1[j] )
  {
   num[count + 1] =  j;
   hash1[j] = true;
   dfs(count + 1);
   hash1[j] = false;
  }
 //return ;
}
int main()
{
 int cas;
 cas = 1;
 memset(hash, false, sizeof(hash));
 hash[2] = true;  hash[3] = true;  hash[5] = true;
 hash[7] = true;  hash[11] = true; hash[13] = true;
 hash[17] = true; hash[19] = true; //hash[21] = true; 一開始這裡弄錯了，糾結啊
 hash[23] = true; hash[29] = true; hash[31] = true;
 hash[37] = true;
 while(cin>>n)
 {
  
  if(n == 1)
  {
   cout<<"Case "<<cas++<<":"<<endl;
   cout<<"1"<<endl<<endl;
   continue;
  }
  memset(hash1, false, sizeof(hash1));
  cout<<"Case "<<cas++<<":"<<endl;
  int count = 1;
  hash1[1] = true;
  num[1] = 1;
  dfs(count);
  cout<<endl;
 }
}