How do you reverse an array in place?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Use two pointers at the start and end and swap until they meet.
WHY — Arrays instead of guessing?
Why interviewers care about Arrays:
question about Arrays.
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:
- 1Use two pointers at
the start and end and swap until they meet.
- 2Each swap is O(1),
so the whole reverse is O(n) time and O(1) extra space.
- 3Mention that creating a
new reversed copy is also O(n) time but uses O(n) space, which interviewers usually do not want.
- 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
Use two pointers at the start and end and swap until they meet. Each swap is O(1), so the whole reverse is O(n) time and O(1) extra space.