253.meeting-rooms-ii.md

253. Meeting Rooms II

Problem

Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],...] (si < ei), find the minimum number of conference rooms required.

Example 1:

Input: [[0, 30],[5, 10],[15, 20]]
Output: 2

Example 2:

Input: [[7,10],[2,4]]
Output: 1

Key Insights

• We need a extra meeting room if there is any overlap between meetings.

[[1, 3], [2, 4]]

1, 2, 3, 4, 5, 6, 7, 8
|-----|                 // Room 1
   |-----|              // Room 2

• But we can reuse a meeting room if the two meetings are not overlapping so that we can have the minimum number of meeting rooms.

[[1, 3], [2, 4], [5, 7]]

1, 2, 3, 4, 5, 6, 7, 8
|-----|     |-----|     // Room 1
   |-----|              // Room 2

NOTE This is a classic problem of finding the maximum number of overlapping intervals at any point of time, and it's a prenium problem on LeetCode, so we move the key notes to 2406. Divide Intervals Into Minimum Number of Groups, the ideas and implementations are the same.