// 8.3 Design a data structure to simulate a musical jukebox.

 #include <iostream>

 #include <queue>

 #include <string>

 #include <thread>

 #include <vector>

 using namespace std;

 class JukeBox {

 public:

     JukeBox() {};

     void start() {

         work = new thread(workThread, this);

     };

     void addSong(vector<int> &song) {

         songs.push_back(song);

     }

     void orderSong(int id) {

         if (id <  || id > (int)songs.size() - ) {

             return;

         }

         song_list.push(id);

     }

     friend void workThread(JukeBox *);

     ~JukeBox() {

         while (!song_list.empty()) {

             song_list.pop();

         }

         size_t i;

         for (i = ; i < songs.size(); ++i) {

             songs[i].clear();

         }

         songs.clear();

         work->detach();

         delete work;

     };

 private:

     queue<int> song_list;

     vector<vector<int> > songs;

     thread *work;

 };

 void workThread(JukeBox *jb) {

     size_t i;

     while (true) {

         if (!jb->song_list.empty()) {

             for (i = ; i < jb->songs[jb->song_list.front()].size(); ++i) {

                 cout << jb->songs[jb->song_list.front()][i] << ' ';

             }

             cout << endl;

             jb->song_list.pop();

         }

     }

 };

 int main()

 {

     JukeBox *jb;

     string cmd;

     int id;

     int i, n;

     vector<int> song;

     jb = new JukeBox();

     jb->start();

     while (cin >> cmd) {

         if (cmd == "add") {

             cin >> n;

             song.resize(n);

             for (i = ; i < n; ++i) {

                 cin >> song[i];

             }

             jb->addSong(song);

         } else if (cmd == "order") {

             cin >> id;

             jb->orderSong(id);

         } else if (cmd == "end") {

             break;

         }

     }

     delete jb;

     return ;

 }