How do you wiggle-sort an array so nums[0] < nums[1] > nums[2] < nums[3] ...?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Find the median with quickselect, then three-way partition virtual indices (Dutch flag on mapped positions) so the small half and large half interleave.
WHY — Sorting instead of guessing?
Why interviewers care about Sorting:
question about Sorting.
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:
- 1Find the median with
quickselect, then three-way partition virtual indices (Dutch flag on mapped positions) so the small half and large half interleave.
- 2Average O(n) time and
O(1) extra space.
- 3Sorting and filling from
the middle is O(n log n) and easier if they allow extra arrays.
- 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
Find the median with quickselect, then three-way partition virtual indices (Dutch flag on mapped positions) so the small half and large half interleave. Average O(n) time and O(1) extra space.