Meeting Room Scheduler

Implement a scheduler for roomCount meeting rooms numbered from 0 to roomCount - 1.
Each row meetings[i] = [start, end] is a request for the half-open interval [start, end). Requests appear in nondecreasing start order and are processed in input order. Assign the lowest-numbered available room. If every room overlaps the request, reject it with -1.
Return an array whose ith value is the assigned room number or -1. A rejected request does not reserve a room.

Function
scheduleMeetings(roomCount: int, meetings: int[][]) → int[]

Examples
Example 1
roomCount = 2
meetings = [[0,10],[5,7],[10,12],[10,15]]
return = [0,1,0,1]
The first two requests occupy rooms 0 and 1. At time 10, both are free; input order gives the third request room 0 and the fourth room 1.
Example 2
roomCount = 1
meetings = [[1,4],[2,3],[4,5]]
return = [0,-1,0]
The second request conflicts with [1,4). The room is available again exactly at time 4.
Example 3
roomCount = 2
meetings = [[1,2],[1,2],[1,2]]
return = [0,1,-1]
Two simultaneous requests take both rooms, so the third request is rejected.

Constraints
1 <= roomCount <= 10^5.
1 <= meetings.length <= 10^5.
meetings[i].length == 2.
0 <= start < end <= 10^9.
Meeting start times are nondecreasing.

The trick is two min-heaps. One holds free room numbers, so the top is always the lowest available room. The other holds busy rooms as (endTime, room) pairs. For each request, pop every busy entry with end <= start and push its room back into the free heap. The half-open interval is why it's <= and not <. Example 2 shows this: a room frees exactly at time 4. Then, if the free heap is empty, answer -1 and change nothing. Otherwise pop the smallest room, record it, and push (end, room) onto the busy heap. Common pitfalls: using < instead of <=, reserving a room for a rejected request, and linear scans over rooms. Start times are nondecreasing, so you never need to sort or rewind. Total cost is O((n + m) log n). If the heap bookkeeping slips under pressure, StealthCoder is the hedge during the live OA.

Drill it cold or hedge it with StealthCoder. Either way, don't walk into the OA hoping you remember the trick.