I went straight for a two-pointer approach and it worked fine, but I spent like two minutes narrating my thought process before writing a single line of code and I could tell the interviewer was just waiting for me to start.
Clarify the problem constraints (e.g., in-place, stability, which end) and then propose an efficient solution like the two-pointer technique. Walk through the algorithm step-by-step, analyze time and space complexity, and discuss edge cases.
Pro tip: Mention that the two-pointer approach is optimal for in-place partitioning, but also note that if stability is required, a different approach like counting and overwriting may be needed. This shows you consider trade-offs beyond just the basic solution.
Ask whether the operation should be in-place, whether zeros should go to the beginning or end, and if the relative order of non-zero elements must be preserved.
Suggest the two-pointer technique: one pointer scans the array, the other marks the position to place the next non-zero (or zero). Alternatively, use counting if stability is required.
Demonstrate the algorithm on a small array, showing how pointers move and elements are swapped or overwritten.
State that the solution runs in O(n) time and O(1) extra space for the in-place two-pointer approach, and discuss trade-offs if using counting.
Cover cases like all zeros, no zeros, single element, and large arrays. Mention that the algorithm handles them correctly.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.