Question

My function search_intersection receive a set <set<string> >& inter_section.

I want get the intersection over all subsets in inter_section.

For example if:

inter_section = { { lion, cat } , {lion, bird}, {lion, cat, bird} }

I want:

result = { lion } 

At the moment I did this

  set<string> search_intersection(set <set<string> >& inter_section)
  {

  set <set<string> >::iterator iter_ss;

  set <string>  result;


  for (iter_ss = inter_section.begin(); iter_ss != inter_section.end(); ++iter_ss)
        {
         set_intersection(iter_ss.begin(),iter_ss.end(),
         result.begin(),result.end(),
          std::inserter(result.begin(),result.end()));
   }

    cout <<  endl;

    return result;
   }

Thanks a lot!

Answer 1

Let’s try again: (Uncompiled code)

set<string> search_intersection(const set <set<string> > &inter_section) {
   set <string>  result;
   set <set<string> >::iterator iter = inter_section.begin ();
   if ( iter != inter_section.end ()) {
      result = *iter;
      for ( ++iter; iter != inter_section.end (); ++iter ) {
         set <string>  temp;
      // intersect *iter and result, put into temp
         set_intersection(
            iter->begin(),  iter->end (),
            result.begin(), result.end(),
            std::inserter(temp,temp.end()));
         result = temp;
         }
   }

   return result;
}

Note that the call to set_intersection passes the begin/end of the set pointed to by the iterator. Also, there are at least two places where const should be applied to this code.

You can’t write the results of set_intersection into one of the inputs, either. Hence a temp variable.