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Meeting Rooms II

Medium
Intervals

Given an array of meeting time intervals where intervals[i] = [start_i, end_i], return the minimum number of conference rooms required.

Key insight: We need to find the maximum number of overlapping meetings at any point in time. This can be solved using:

  1. Min-heap approach: Sort by start time. Use a min-heap to track meeting end times. For each meeting, remove all ended meetings, then add the current one.

  2. Event-based approach: Create separate arrays for start and end times. Sort both. Use two pointers to count active meetings.

  3. Sweep line: Mark +1 at each start, -1 at each end. The maximum running sum is the answer.

Real-world analogy: You're a facility manager figuring out how many conference rooms to book for a day's meetings.

Example 1

Input: intervals = [[0,30],[5,10],[15,20]]
Output: 2
Explanation: At time 5, both [0,30] and [5,10] are active. At time 15, [0,30] and [15,20] are active. Maximum 2 rooms needed.

Example 2

Input: intervals = [[7,10],[2,4]]
Output: 1
Explanation: These meetings do not overlap. One room is sufficient.

Example 3

Input: intervals = [[1,5],[2,6],[3,7],[4,8]]
Output: 4
Explanation: At time 4, all four meetings are active simultaneously.

Constraints

  • •1 <= intervals.length <= 10^4
  • •0 <= start_i < end_i <= 10^6
Show Hints (4)
Hint 1: Think about what happens at each point in time. How many meetings are active?
Hint 2: Could you use a min-heap to track which meetings have ended?
Hint 3: Alternative: separate the start and end times into two arrays.
Hint 4: The answer is the maximum number of concurrent meetings.
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