Untitled

int announce(int mDuration, int M) {
    TreeSet<Employee> set = new TreeSet<>((a, b) -> a.end - b.end);
    for (Employee e : set) {
        set.add(e);
        int announceEnd = e.start + mDuration - 1;
        while (!set.isEmpty() && set.first().end < announceEnd)
            set.pollFirst();
        if (set.size() == M)
            return e.start;
    }
    return -1;
}