Given a list of meetings for a given day in a conference center, return a list
of time slots during which the most number of concurrent meetings are held.
Each meeting has a start time and end time and occupies a single room in a
conference center.

Input:
(100,300) // meeting 1, 1:00 am to 3:00 am
(145,215) // meeting 2
(200,230) // meeting 3
(215,300) // meeting 4
(215,400) // meeting 5
(500,600) // meeting 6
(600,700) // meeting 7

Output:
(215,230) // 4 concurrent meetings: 1,3,4,5

Last question in my second round onsite interview, could not figure this out for the life of me. This was for New Grad NYC position. I can write up a full onsite experience if requested.