Snapchat·Machine Learning Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Snapchat ML engineer interview with a binary search coding round. Pretty focused on correctness and being able to talk through your reasoning, not just getting to an answer.

Questions Asked (1)

Implement binary search or a variant (like lower_bound, upper_bound, or find first/last occurrence), and walk through your loop invariants and how you handle edge cases such as an empty array, a single element, a target outside the range, and duplicates.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I went with lower_bound first since it felt cleaner to reason about.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem and choosing a specific variant (e.g., lower_bound) to implement. Write clean code with clear invariants, then walk through edge cases and test with examples. Emphasize how invariants ensure correctness and how edge cases are handled.

Pro tip: Relate binary search to ML engineering tasks like hyperparameter tuning or threshold optimization, and mention how invariants prevent off-by-one errors in production code.

1. Clarify requirements and choose variant

Ask clarifying questions to confirm the exact behavior needed (e.g., find first occurrence). State which variant you will implement and why.

2. Define loop invariants and write code

Clearly state the invariant (e.g., answer lies in [lo, hi]) and write the loop ensuring it holds. Use consistent bounds and update rules.

3. Walk through edge cases

Explicitly test empty array, single element, target outside range, and duplicates. Explain how the code handles each.

4. Analyze complexity and trade-offs

State O(log n) time and O(1) space. Discuss trade-offs between variants (e.g., lower_bound vs upper_bound) and when to use each.

5. Connect to ML engineering context

Mention applications like finding optimal thresholds, quantiles, or searching sorted model outputs, showing relevance to the role.

Key Points to Mention

Loop invariant definition and maintenance
Handling empty array (return -1 or appropriate value)
Single element array behavior
Target outside range (early termination or return -1)
Duplicates: finding first/last occurrence with modified conditions
Time and space complexity (O(log n) time, O(1) space)

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