include <list>
  include <vector>
  include <string>
  include <algorithm>
  include <iterator>
  include <fstream>
  include <iostream>
  include <sstream>
  using namespace std;
  
  //
  // classLists is a vector of lists, one for each course. The lists
  // contain the students enrolled in those courses. They are not sorted.
  //
  // droppedStudents is a list of students who failed to pay their
  // tuition, so are dropped from their courses.
  //
  // The function returns a list of every enrolled (non-dropped) student in
  // all the courses
  //
  list<string>
  getTotalEnrollment(const vector<list<string> >& classLists,
                     const list<string>& droppedStudents)
  {
    list<string> allStudents;
  
    // Concatenate all the course lists onto the master list
    for (size_t i = 0; i < classLists.size(); ++i) {
      allStudents.insert(allStudents.end(), classLists[i].begin(),
                         classLists[i].end());
    }
  
    // Sort the master list
    allStudents.sort();
  
    // Remove duplicate student names (those who are in multiple courses).
    allStudents.unique();
  
    //
    // Remove students who are on the dropped list.
    // Iterate through the drop list, calling remove on the
    // master list for each student in the dropped list.
    //
    for (list<string>::const_iterator it = droppedStudents.begin();
         it != droppedStudents.end(); ++it) {
      allStudents.remove(*it);
    }
  
    // done!
    return (allStudents);
  }
  
  void readStudentList(list<string> &students, ifstream &istr)
  {
    string name;
    while (getline(istr, name)) {
      cout << "Read name " << name << endl;
      students.push_back(name);
    }
  }
  
  void readCourseLists(vector<list<string> > &lists)
  {
    for(int i = 1; ; i++) {
      ostringstream ostr;
      ostr << "course" << i << ".txt";
  
      ifstream istr(ostr.str().c_str());
      if (!istr) {
        cout << "Failed to open " << ostr.str() << endl;
        break;
      }
      list<string> newList;
      readStudentList(newList, istr);
      lists.push_back(newList);
    }
  }
  
  void readDroppedStudents(list<string> &students)
  {
    ifstream istr("dropped.txt");
    readStudentList(students, istr);
  }
  
  int main(int argc, char **argv)
  {
    vector<list<string> > courseLists;
    list<string> droppedStudents;
  
    readCourseLists(courseLists);
    readDroppedStudents(droppedStudents);
  
    list<string> finalList = getTotalEnrollment(courseLists, droppedStudents);
  
    copy(finalList.begin(), finalList.end(), ostream_iterator<string>(cout, "\n"));
  }