Meeting Rooms II

Problem
Given an array of meeting time intervals [start, end], return the minimum number of conference rooms required so that no two meetings sharing a room overlap in time.

Input / Output

• Input: an array of intervals [start, end].
• Output: the minimum number of rooms needed.

Constraints

• 1 ≤ n ≤ 10^4.
• A meeting ending at time t and another starting at t do not conflict (can share a room).

Example

• [[0,30],[5,10],[15,20]] → 2 ([0,30] overlaps both others, which do not overlap each other).
• [[7,10],[2,4]] → 1.