on test # 1......................
if i get it again, i'm gonna break something....
it runs perfectly on my compiler


#include <stdio.h>
#include <iostream>
#include <vector>
#define PB push_back

using namespace std;

int lev[110];

int main()
{
  int i,j,k,l,n,s,e,v;
  int q[10100];
  vector<int> a[110];
  scanf("%d",&n);
//  cin>>n;
  for (i=1; i<=n; i++)
   {
     while (1)
     {
      scanf("%d",&j);
//  cin>>j;
      if (j!=0) a[i].PB(j); else break;
     }
   }


  for (i=1; i<=n; i++)
  if (!lev[i])
{
  q[0]=i; e=0;
  for (s=0; s<=e; s++)
   {
      for (j=0; j<a[q[s]].size(); j++)
       {
        v=a[q[s]][j];
        lev[v]=lev[q[s]]+1;
        q[e++]=v;
       }
   }
}

  vector<int> ans;
  for (i=1; i<=n; i++)
   if (lev[i]%2) ans.PB(i);

  printf("%d\n",ans.size());
  for (i=0;i<ans.size()-1; i++)
   printf("%d ",ans[i]);
  printf("%d\n",ans[ans.size()-1]);

  return 0;
}

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0

Every member has one or more friends in the group!!!

> Every member has one or more friends in the group!!!

The problem statement does not say this.  It says that friendship is mutual (the friendship must exist for this to be true), and  that the friendship list is terminated by a 0.   So it is allowed for a member to have no friends.