253. Meeting Rooms II

Given meeting time intervals, return the minimum number of conference rooms needed so that no two overlapping meetings share a room.

Turn each meeting into a +1 at its start and a −1 at its end. Sort the events (ends before starts at the same time) and track the running total.

1function minMeetingRooms(intervals: number[][]): number {
2  const events = intervals.flatMap(([s, e]) => [[s, 1], [e, -1]]);
3  events.sort((a, b) => a[0] - b[0] || a[1] - b[1]);
4  let cur = 0, best = 0;
5  for (const [, delta] of events) {
6    cur += delta;
7    best = Math.max(best, cur);
8  }
9  return best;
10}

rooms in use = 0best = 0

events (time, +start / −end)

10−

10+

15+

18−

20−

30−

Build and sort the events.

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