How do you move all zeros to the end while keeping the relative order of other elements?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Keep a write index for the next non-zero slot
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:
- 1Keep a write index
for the next non-zero slot
- 2scan left to right
and copy every non-zero forward, then fill the tail with zeros.
- 3That is one O(n)
pass and O(1) extra space.
- 4A two-array copy also
works but wastes O(n) space, which you should mention as the naive option.
- 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
Keep a write index for the next non-zero slot scan left to right and copy every non-zero forward, then fill the tail with zeros.