How do you find the minimum number of meeting rooms required?

Q: How do you find the minimum number of meeting rooms required?

**Target Audience:** Beginners preparing for coding interviews — you need sorting and arrays in Python; heaps are explained here. **Difficulty:** Medium **Language:** Python 3 > **How to read this doc:** every idea is explained in plain words first. When a word appears that an interviewer will expect you to know, it is tagged `📌 Interview term:` with a one-line definition, and every tagged term is collected in the Quick Glossary at the end. Every program on this page was actually run, and the output you see in the **Verified** section is copied from that run. ## 1. Why This Even Matters — A Story First You run a small office with a list of today's meetings: one from 0:00 to 0:30, one from 0:05 to 0:10, one from 0:15 to 0:20 (minutes after nine, say). How many meeting rooms do you need so that nobody is left standing in the corridor? You could give every meeting its own room — three rooms — but that is wasteful: the 0:05 meeting is over by 0:10, so its room is free again for th

The problem

Question presented to candidate: "Given a list of meetings as [start, end] pairs, write a Python function that returns the minimum number of conference rooms needed so that no two overlapping meetings share a room."

What a strong answer should cover:

The answer is the maximum number of meetings running at the same time.
Sort by start, keep a min-heap of end times; reuse the room on top when its end is <= the new start, otherwise open a room. O(n log n) time, O(n) space.
The sweep-line alternative: +1/−1 events sorted by time, ends before starts on ties.
Edge cases: back-to-back meetings share a room, identical meetings need separate rooms, empty input is 0.
Python details: heapq is a min-heap on a plain list (ends[0] is the smallest), heapq.heapreplace pops and pushes in one call, and sorted() on tuples orders ends before starts when you encode them as (time, -1) and (time, +1).

Clarifying questions expected:

Can a meeting ending at 10 share a room with one starting at 10?
Is the input already sorted?

Code / implementation expected: Yes — a function min_meeting_rooms(meetings) -> int using heapq, in Python 3.

intervals
sorting
heap

Try it yourself

Sketch your approach before you read the solution. That is what the interview tests.

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A short nudge toward the approach. It will not give the answer away.

Solution

Target Audience: Beginners preparing for coding interviews — you need sorting and arrays in Python; heaps are explained here.
Difficulty: Medium
Language: Python 3

How to read this doc: every idea is explained in plain words first. When a word appears that an interviewer will expect you to know, it is tagged 📌 Interview term: with a one-line definition, and every tagged term is collected in the Quick Glossary at the end. Every program on this page was actually run, and the output you see in the Verified section is copied from that run.

1. Why This Even Matters — A Story First

You run a small office with a list of today's meetings: one from 0:00 to 0:30, one from 0:05 to 0:10, one from 0:15 to 0:20 (minutes after nine, say). How many meeting rooms do you need so that nobody is left standing in the corridor?

You could give every meeting its own room — th

The solution is hidden so you can try first

5 min read · 11 sections

Python code

Edit the code and run it here. Each printed line with an expected value becomes a test.

PythonSort by start + min-heap of end times (7 schedules)

Practice

PythonSweep line trace + random cross-check of three methods

Practice

Discussion

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