<p>A <code>k</code>-booking happens when <code>k</code> events have some non-empty intersection (i.e., there is some time that is common to all <code>k</code> events.)</p>
<p>You are given some events <code>[startTime, endTime)</code>, after each given event, return an integer <code>k</code> representing the maximum <code>k</code>-booking between all the previous events.</p>
<li><code>int book(int startTime, int endTime)</code> Returns an integer <code>k</code> representing the largest integer such that there exists a <code>k</code>-booking in the calendar.</li>