Meeting Rooms II

medium

Find minimum number of conference rooms needed

Meeting Rooms II

Key Insight

Sort starts and ends; sweep with two pointers to count how many meetings overlap at any time.

Step 1Sort Start and End Arrays
starts sortedends sorted
[0,5,15]
0
[10,10,20]
1

Start list: [0, 5, 15], end list: [10, 10, 20] after sorting.

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Learn the Pattern

SortingUse sorting as a preprocessing step to simplify problems, or apply partition logic for in-place rearrangement. Many interview problems become trivial once the array is sorted.
HeapUse a heap (priority queue) when you repeatedly need the minimum or maximum of a changing set while also inserting and deleting values efficiently.
Practice the Code

Step-by-Step Walkthrough: Meeting Rooms II

Sort starts and ends; sweep with two pointers to count how many meetings overlap at any time.

  1. Sort Start and End Arrays

    Start list: [0, 5, 15], end list: [10, 10, 20] after sorting.

  2. Sweep and Allocate

    Compare current start with current end. If start < end, overlaps require one more room.

  3. Release and Continue

    When a meeting ends, reuse that room by moving end pointer.

  4. Result

    The peak concurrent count is the minimum rooms needed.