Meeting Rooms in Scala

Given an array consisting of meeting time intervals, which are represented by the start and end times ([s0, e0], [s1, e1], ...], determine the minimum number of meeting rooms needed in order to be able to accomodate all meetings at every moment of time.

Example:

Input: [[5, 10], [0, 30], [15, 20]]
Output: 2
Explanation: 1st and 3rd meetings can be assigned to the first room
             2nd meeting can be assigned to room 2

Note:

1. You may assume the interval's end point is always greater than its start point.
2. Intervals like [1,2] and [2,3] have borders "touching" but they don't overlap.

Your algorithm should run in O(n log n) time and use O(n) extra space.