Meta·Machine Learning Engineer·Technical Phone Screen·Senior

Senior

Jul 2026

Summary

Meta ML Engineer interview with a coding question that was more about careful implementation than raw algorithmic complexity. The problem itself wasn't hard but the details tripped me up a bit.

Questions Asked (1)

Given a working maze traversal solution that marks every path cell with '*', modify it so the start and end markers are preserved in the rendered output instead of being overwritten.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I went straight to storing the endpoint coordinates and checking against them during the marking step, which worked fine.

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AI HintsAI Generated

Suggested Approach

First, clarify that the current solution overwrites start and end markers during traversal. Then, propose modifying the marking logic to check if a cell is the start or end before marking, or alternatively, record the start and end positions and reapply their markers after traversal. Finally, discuss the trade-offs of each approach in terms of code simplicity and performance.

Pro tip: Mention that preserving markers is a common requirement in visualization and debugging, and that a clean solution often involves separating traversal logic from rendering logic. This shows you think about maintainability and separation of concerns.

1. Identify the issue

Explain that the current traversal marks all visited cells with '*', including the start and end, which overwrites their original markers.

2. Choose a strategy

Decide between conditional marking (skip marking if cell is start or end) or post-processing (reapply markers after traversal). Consider code clarity and performance.

3. Implement conditional marking

Modify the marking step to check if the current cell is the start or end; if so, do not overwrite its marker. This avoids extra passes.

4. Or implement post-processing

After traversal, set the start and end cells back to their original markers. This is simpler if traversal logic is complex.

5. Discuss trade-offs

Compare approaches: conditional marking is efficient but adds a check per cell; post-processing is simpler but requires storing positions and an extra pass.

Key Points to Mention

Preserving start and end markers is important for output readability and debugging.
Conditional marking avoids overwriting but adds a conditional check in the inner loop.
Post-processing is straightforward but requires storing start/end coordinates and an extra iteration.
Separation of concerns: traversal logic should not be coupled with rendering logic.
Time complexity remains O(N) for both approaches, but constant factors may differ.
Edge cases: start and end might be the same cell, or markers might be multi-character strings.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.