P60219: Easy game?

#include <iostream>
#include <set>
using namespace std;


struct strsize{
  bool operator() (const string& a, const string& b) const {
    if (a.size() < b.size()) return true;
    else if (a.size() > b.size()) return false;
    else return a < b;
  }
};

int main() {
  int count = 1;
  string s;
  set<string>::iterator it1;
  set<string, strsize>::iterator it2;
  while (s != "QUIT") {
    set<string> has;
    set<string,strsize> had;
    while (cin >> s && s != "END" && s != "QUIT") {
      it1 = has.find(s);
      if (it1 == has.end()) {
    has.insert(it1,s);
    it2 = had.find(s);
    if (it2 != had.end()) had.erase(it2);
      }
      else {
    it2 = had.begin();
    had.insert(it2,*it1);
    has.erase(it1);
      }
    }
    if (count > 1) cout << endl;
    cout << "GAME #" << count << endl << "HAS:" << endl;
    for (it1 = has.begin(); it1 != has.end(); ++it1) cout << *it1 << endl;
    cout << endl << "HAD:" << endl;
    for (it2 = had.begin(); it2 != had.end(); ++it2) cout << *it2 << endl;
    ++count;
  }
}

//JosepRivaille