253. Meeting Rooms II

Given an array of meeting time intervals intervals where intervals[i] = [starti, endi], return the minimum number of conference rooms required.

def minMeetingRooms(intervals: List[List[int]]):
       
    if not intervals:
        return 0

    usedRooms = 0

    # Separate out the start and the end timings and sort them individually.
    starts = sorted([i[0] for i in intervals])
    ends = sorted(i[1] for i in intervals)
    L = len(intervals)

    start, end = 0, 0        

    while start < L:
        # If there is a meeting that has ended by the time the meeting at `start` starts
        if starts[start] >= ends[end]:
            usedRooms -= 1
            end += 1

        # We do this irrespective of whether a room frees up or not.
        # If a room got free, then this used_rooms += 1 wouldn't have any effect.
        # used_rooms would remain the same in that case.
        # If no room was free, then this would increase used_rooms
        usedRooms += 1    
        start += 1  

    return usedRooms

















def minMeetingRooms(intervals: List[List[int]]):
   
    if not intervals:
        return 0

    usedRooms = 0        
    minRooms = 0
   
    starts = [(i[0], 1) for i in intervals]
    ends = [(i[1], -1) for i in intervals]
   
    events = sorted(starts + ends)
       
    for _, event in events:            
        usedRooms += event          
        minRooms = max(minRooms, usedRooms)
   
    return minRooms

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