#include <iostream>
using namespace std;
long f[101],n;
int main()
  {
    long i,t,c=0;
    cin>>n;
    for (i=1;i<=n;i++)
      {
        if (f[i]==0) f[i]=1;
        while (true)
          {
            cin>>t;
            if (t==0) break;
            if (f[t]==0) f[t]=1+(f[i]==1);
          }
        if (f[i]==1) c++;
      }
    cout<<c<<endl;
    for (i=1;i<=n;i++)
        if (f[i]==1) cout<<i<<" ";
  }

why??

I had WA 11, this test helped me:

4
2 0
1 4 0
4 0
2 3 0

Edited by author 30.10.2007 04:07

Thank You!

thanks

What's the main idea behind it?