import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class Monitor {

    private LinkedList<Integer> tallListe = new LinkedList<>();
    private Lock laas = new ReentrantLock();
    private Condition tomListe = laas.newCondition();
    private int antallTraader;

    public Monitor(int antallTraader){
        this.antallTraader = antallTraader;
    }

    public void leggTil(int tall){
        laas.lock();
        try{
            tallListe.add(tall);
            tomListe.signalAll();
        }finally{
            laas.unlock();
        }
        
    }

    public void ferdig(){
        laas.lock();
        try{
            antallTraader--;
        }finally{
            laas.unlock();
        }
    }

    //Hente ut to tall
    public List<Integer> hentTo(){
        laas.lock();
        try {
            while(tallListe.size() < 2){
                if(antallTraader == 0) return null;
                tomListe.await();
            }
            List<Integer> returnTall = new ArrayList<>(2);
            returnTall.add(tallListe.remove());
            returnTall.add(tallListe.remove());
            return returnTall;
        } catch (Exception e) {
            return null;
        }finally{
            laas.unlock();
        }
    }
    
}