Openai·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Coding round at OpenAI for a software engineer role, one problem centered on building a chatbot system. The problem wasn't technically brutal but the real test was whether your design could handle future changes without touching existing code.

Questions Asked (1)

Implement a ChatApp class that manages user messages and bot responses, designed so that new bot types can be added later without modifying existing code.

System DesignTechnical Trade-offsAPI & Integrations

Author's notes

I got the core logic down fine but the bot registration part tripped me up.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then design a ChatApp class that uses the Strategy pattern to encapsulate bot behaviors, allowing new bot types to be added via new classes without modifying existing code. Discuss trade-offs such as extensibility vs. complexity, and mention how dependency injection or a factory can manage bot instances.

Pro tip: Emphasize the Open/Closed Principle and show how your design avoids modifying existing code when adding new bots, but also discuss potential pitfalls like over-engineering and how to balance flexibility with simplicity.

1. Clarify Requirements

Ask questions to understand the scope: What types of bots? How are messages routed? Are there performance or concurrency concerns? This ensures your design meets actual needs.

2. Identify Core Abstractions

Define interfaces for Bot and Message, and a ChatApp class that manages users and delegates message handling to bots. This sets the foundation for extensibility.

3. Apply Design Patterns

Use the Strategy pattern for bot behaviors and a Factory or Registry to instantiate bots. This allows adding new bot types without modifying ChatApp.

4. Discuss Trade-offs

Compare approaches: inheritance vs. composition, simple if-else vs. polymorphic dispatch. Highlight how your choice supports the Open/Closed Principle while keeping code maintainable.

5. Outline Implementation

Sketch the class structure and key methods, showing how a new bot can be plugged in. Mention testing and how to handle bot registration dynamically.

Key Points to Mention

Open/Closed Principle: classes should be open for extension but closed for modification.
Strategy pattern to encapsulate interchangeable bot algorithms.
Factory or dependency injection to manage bot creation and registration.
Interface segregation: define minimal Bot interface with a respond method.
Trade-offs: flexibility vs. complexity, and when to choose simpler solutions.
Extensibility: how new bots can be added without changing ChatApp code.

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