How do you implement a stack with an array, and what are the operation costs?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Store items in a list and treat the end as the top: append to push, pop from the end to pop, and peek the last index.
WHY — Stack instead of guessing?
Why interviewers care about Stack:
question about Stack.
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:
- 1Store items in a
list and treat the end as the top: append to push, pop from the end to pop, and peek the last index.
- 2Amortized O(1) push/pop if
the array resizes geometrically
- 3peek and empty checks
are O(1).
- 4Mention overflow if the
interviewer wants a fixed-capacity array.
- 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
Store items in a list and treat the end as the top: append to push, pop from the end to pop, and peek the last index. Amortized O(1) push/pop if the array resizes geometrically