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Scale.ai·Machine Learning Engineer·Technical Phone Screen·Intermediate

IntermediatePass
Jun 2026

Summary

Three-part coding interview for an ML Engineer role at Scale.ai. Finished all parts in an hour and passed every test, but the interviewer was basically silent the whole time which made it feel like talking into a void.

Questions Asked (2)

Q1

Implement an updateDeadline function that checks if a task has already been consumed before updating its deadline, returning null if so.

Algorithms & Data StructuresAPI & Integrations
Author's notes

This was part 3 of a multi-part coding problem.

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AI HintsAI Generated

Suggested Approach

Clarify the data model and consumption semantics first, then outline a function that checks the task's consumed status before updating the deadline, returning null if consumed. Discuss edge cases like missing tasks, invalid deadlines, and concurrency, and propose tests to validate the behavior.

Pro tip: Mention that returning null for consumed tasks is a deliberate API contract choice, and suggest logging or metrics to track attempts to update consumed tasks, which helps with debugging and monitoring in production ML pipelines.

1. Clarify requirements and data model

Ask about the task object structure, how 'consumed' is represented, and whether the function should mutate in place or return a new object. Confirm the expected return type and error handling.

2. Design the function signature and logic

Define the function parameters (e.g., task ID, new deadline) and outline the check: if task is consumed, return null; otherwise update the deadline and return the updated task.

3. Handle edge cases and concurrency

Consider missing tasks, invalid deadline formats, and race conditions where a task might be consumed between check and update. Propose atomic operations or locking if needed.

4. Implement and test

Write clean code with clear comments, then outline unit tests covering normal update, consumed task, missing task, and concurrent scenarios.

5. Discuss integration and monitoring

Explain how this function fits into the larger system, and suggest logging or metrics for attempts to update consumed tasks to aid observability.

Key Points to Mention

  • Clear definition of 'consumed' status and how it's stored (e.g., boolean flag, timestamp, state enum).
  • Return null as an explicit API contract for consumed tasks, and document it.
  • Idempotency and concurrency: ensure the check-and-update is atomic or handled with optimistic locking.
  • Validation of the new deadline (e.g., future date, correct format) before updating.
  • Error handling for non-existent tasks (e.g., return null or throw specific exception).
  • Testing strategy including unit tests for edge cases and integration tests with the task queue.

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

Q2

What is the time complexity of your solution?

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

Only came up right at the end, after all three parts were done.

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AI HintsAI Generated

Suggested Approach

Start by clearly stating the time complexity using Big-O notation, then briefly explain how you derived it by analyzing the loops, recursion, or operations in your code. Also mention space complexity if relevant, and discuss any trade-offs you made between time and space.

Pro tip: Always relate the complexity to the input size and mention best, average, and worst cases if they differ. If you optimized from a brute-force solution, explain the improvement to show your problem-solving process.

1. State the complexity

Clearly state the time complexity in Big-O notation, e.g., O(n log n). If there are multiple parts, specify the overall complexity.

2. Explain the derivation

Walk through the code or algorithm, identifying the dominant operations and how they scale with input size. For example, nested loops multiply, sequential loops add.

3. Mention space complexity

If relevant, state the space complexity and explain how extra data structures or recursion contribute to it.

4. Discuss trade-offs

If you made a trade-off (e.g., using extra space to reduce time), explain why it was beneficial and any alternatives considered.

5. Consider edge cases

Mention if the complexity changes for best, average, or worst-case scenarios, and how it handles edge cases like empty input.

Key Points to Mention

  • Big-O notation and why it's used to describe asymptotic behavior
  • How to analyze loops, recursion, and built-in operations
  • Time vs. space trade-offs and when they matter
  • Best, average, and worst-case complexities
  • Input size and how it affects performance
  • Optimizations made and their impact on complexity

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