Openai·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Interviewed at OpenAI for a software engineering role and got a design question that looked clean on the surface but had some tricky state management hiding underneath.

Questions Asked (1)

Design and implement a SocialNetwork class that supports adding users, following other users, creating snapshots of the follow graph, and querying whether a user followed another user at a specific snapshot.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs

Author's notes

The add/follow parts were fine, took maybe five minutes.

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AI HintsAI Generated

Suggested Approach

Clarify the requirements and constraints first, then propose a design that balances time and space efficiency. Discuss trade-offs between different data structures and snapshot strategies, and outline the implementation details with complexity analysis.

Pro tip: Mention that snapshots can be implemented using versioned edges or persistent data structures to avoid full copies, and discuss how this scales with many snapshots.

1. Clarify Requirements

Ask about expected scale (number of users, follows, snapshots), snapshot frequency, and query patterns to guide design decisions.

2. Design Data Structures

Choose structures for users, follow relationships, and snapshots. Consider adjacency lists, hash maps, and versioning for efficient updates and queries.

3. Implement Snapshot Mechanism

Decide between full copy, copy-on-write, or versioned edges. Explain how to capture the state at a given time and support queries at that snapshot.

4. Analyze Trade-offs

Compare time and space complexity of different approaches, and discuss scalability, concurrency, and persistence considerations.

5. Outline Implementation

Sketch the class methods (addUser, follow, snapshot, query) and provide pseudocode or key implementation details.

Key Points to Mention

Time and space complexity of operations (add, follow, snapshot, query)
Snapshot strategies: full copy vs. versioned edges vs. persistent data structures
Handling concurrent updates and snapshots (if relevant)
Scalability considerations for large graphs and many snapshots
Trade-offs between query speed and snapshot creation cost
Edge cases: self-follow, duplicate follows, non-existent users

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