253. Meeting Rooms II

To find out the number of concurrent meetings, we can merge the start/end times into one array keyed by timestamp + the action (if a meeting starts, one more meeting room is required, and if a meeting ends, one less meeting room is required). We then calculate the maximum number of concurrent meetings and return that.

class Solution:
    def minMeetingRooms(self, intervals: List[List[int]]) -> int:
        times = []
 
        for start, end in intervals:
            times.append((start, +1))
            times.append((end, -1))
        
        times.sort()
 
        max_rooms, curr_rooms = 0, 0
 
        for _, meeting in times:
            curr_rooms += meeting
            max_rooms = max(max_rooms, curr_rooms)
        
        return max_rooms