How does the activity-selection problem work?
PICTURE THIS: HOW TO EXPLAIN IT
Simple meaning
Sort activities by finish time and repeatedly pick the next one that starts after the last chosen finish.
WHY — Greedy instead of guessing?
Why interviewers care about Greedy:
question about Greedy.
trade-offs, and what you would actually do on a DSA project - not buzzwords.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Sort activities by finish
time and repeatedly pick the next one that starts after the last chosen finish.
- 2Sorting is O(n log
n) and the scan is O(n), with O(1) extra space besides the sort.
- 3Picking longest duration first
is not optimal, which is the usual trap.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Sort activities by finish time and repeatedly pick the next one that starts after the last chosen finish. Sorting is O(n log n) and the scan is O(n), with O(1) extra space besides the sort.