3 0 30 5 10 15 20
The first meeting overlaps each of the other two, so two rooms are enough and necessary.
2
3 1 2 2 3 3 4
Meetings that touch at endpoints can reuse the same room, so one room is enough.
1
4 1 5 2 6 4 8 8 9
At time 4, three meetings are active, so the answer is 3.
3
Given meeting intervals [li,ri)[l_i, r_i)[li,ri), find the minimum number of rooms needed so every meeting can be scheduled.