How do you square a sorted array (possibly with negatives) and return a sorted result?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Squares of a sorted array are largest at the ends.
WHY — Two Pointers instead of guessing?
Why interviewers care about Two Pointers:
question about Two Pointers.
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:
- 1Squares of a sorted
array are largest at the ends.
- 2Two pointers fill a
result from the back by always taking the larger absolute value.
- 3Time is O(n) and
space is O(n) for the output, beating map-then-sort at O(n log n).
- 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
Squares of a sorted array are largest at the ends. Two pointers fill a result from the back by always taking the larger absolute value.