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Openai·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Jun 2026

Summary

Did a technical round at OpenAI for a software engineer role. The problem sounded simple until it wasn't, basically a key-value store with a serialization twist baked in.

Questions Asked (1)

Q1

Implement a key-value store with put, get, and delete operations, where values are structured objects that must be serialized to strings for storage. You need to define the serialization format and ensure values survive a round-trip correctly.

System DesignTechnical Trade-offsAPI & Integrations
Author's notes

I went straight for the basic operations and got those working fine, but then the serialization part tripped me up more than I expected.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a serialization format (e.g., JSON) with a clear schema, and implement the key-value store with put, get, and delete operations. Emphasize round-trip correctness through testing and discuss trade-offs of your choices.

Pro tip: Mention that you would version the serialized format to handle schema evolution, and use a library like JSON Schema for validation to ensure data integrity.

1. Clarify Requirements

Ask about expected data types, size limits, concurrency needs, and persistence requirements to scope the solution appropriately.

2. Choose Serialization Format

Select a format like JSON or MessagePack, justifying based on readability, performance, and compatibility with structured objects.

3. Design API and Storage

Define put(key, value), get(key), delete(key) methods, and decide on an in-memory map or external store, ensuring serialization on write and deserialization on read.

4. Ensure Round-Trip Correctness

Implement serialization and deserialization functions, and write tests to verify that objects survive the round-trip without data loss.

5. Discuss Trade-offs and Extensions

Talk about performance, error handling, schema evolution, and potential optimizations like caching or compression.

Key Points to Mention

  • Choice of serialization format (e.g., JSON, Protocol Buffers) and its trade-offs
  • Handling of special data types (dates, binary data) during serialization
  • Error handling for serialization/deserialization failures
  • Concurrency control if the store is accessed by multiple threads
  • Testing strategy for round-trip correctness, including edge cases
  • Versioning of serialized data to support schema evolution

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