Task Y eventsStore

package events;

import java.util.*;

public class EventsStoreImpl implements EventsStore {

    Map<Integer, Set<Integer>> usersByTime;

    public EventsStoreImpl()
    {
        usersByTime = new TreeMap<>();
    }


    @Override
    public void registerEvent(int userId, int time) {

        Set<Integer> s = usersByTime.getOrDefault(time, new HashSet<>());
        if(s == null)
            s = new HashSet<>();

        s.add(userId);
        usersByTime.put(time, s);

        int startTime = time - FIVE_MINUTES;
        for (Iterator<Map.Entry<Integer, Set<Integer>>> it = usersByTime.entrySet().iterator(); it.hasNext(); )
        {

            if (startTime > it.next().getKey())
            {
                it.remove();
            }
            else
                break;
        }

    }

    @Override
    public int queryCountOfUsersWithNEventsInLast5Minutes(int n, int time) {
        int startTime = time - FIVE_MINUTES;
        Map<Integer, Integer> users = new HashMap<>();
        for (Map.Entry<Integer, Set<Integer>> e : usersByTime.entrySet())
        {
            if (startTime <= e.getKey())
            {
                for (Integer user : e.getValue())
                {
                    int count = users.getOrDefault(user, 0);
                    count++;
                    users.put(user, count);
                }
            }
        }

        Set<Integer> ans = new HashSet<>();
        for (Map.Entry<Integer, Integer> e : users.entrySet())
        {
            if (e.getValue() == n)
            {
                ans.add(e.getKey());
            }
        }
        return ans.size();
    }
}