Practice My Calendar II

MyCalendarTwo.book(startTime,endTime) adds a half-open event only if no time would become covered by three events. Return true on acceptance or false without mutation on rejection; double overlaps are allowed. Practice approach: Keep accepted events and their double-covered intersections. Reject a new event if it overlaps any double-covered interval. Otherwise add intersections with existing events and store the event. Alternatively, use an endpoint sweep and roll back tentative changes on rejection. Test identical intervals and touching endpoints.