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Openai·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Jun 2026Remote

Summary

Interviewed at OpenAI for what seemed like a software engineering role. One coding question the whole time, basically build a mini interpreter from scratch. Not the hardest thing I've done but there were definitely a few moments where I second-guessed my approach.

Questions Asked (1)

Q1

Given a list of instructions in a simple toy programming language (like 'SET x 5', 'ADD x 3', 'PRINT x'), write an interpreter that runs those instructions and prints the output of any PRINT commands.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

My first instinct was to reach for something overly clever, like building a class hierarchy for each instruction type.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the language specification and edge cases, then outline a simple interpreter architecture with a tokenizer/parser if needed, or direct execution. Implement a loop that processes each instruction, maintaining a variable environment, and handle PRINT by outputting the variable's value.

Pro tip: Discuss trade-offs between a simple switch-based interpreter and a more extensible design using a dispatch table or command pattern, showing awareness of maintainability and performance.

1. Clarify Requirements

Ask about the exact syntax, variable naming rules, error handling, and whether instructions are case-sensitive. Confirm input/output format and any constraints.

2. Design Interpreter Architecture

Decide on a simple loop-based interpreter or a more modular design with separate parsing and execution phases. Consider extensibility for future commands.

3. Implement Core Components

Create a data structure for variables (e.g., hash map) and a dispatcher for commands. For each instruction, parse the operation and arguments, then execute accordingly.

4. Handle Edge Cases and Errors

Define behavior for undefined variables, invalid commands, and type mismatches. Implement error reporting or graceful handling as appropriate.

5. Test and Validate

Write test cases covering basic operations, edge cases, and error conditions. Verify output matches expectations and discuss potential optimizations.

Key Points to Mention

  • Choice of data structure for variable storage (e.g., hash map for O(1) access)
  • Parsing strategy: splitting strings vs. tokenization for complex syntax
  • Error handling: undefined variables, invalid commands, and type errors
  • Extensibility: using a dispatch table or command pattern to add new instructions easily
  • Performance considerations: time and space complexity of the interpreter
  • Testing approach: unit tests for individual commands and integration tests for full programs

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