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Openai·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

Interviewed for a software engineering role at OpenAI. The coding question was a twist on IP address manipulation, specifically extending IPv4 logic to support incrementing and decrementing addresses. Short session, not a lot of back-and-forth.

Questions Asked (1)

Q1

Implement a function that takes an IPv4 address and supports navigating to the next or previous address by incrementing or decrementing it.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

Seemed straightforward at first but the carry logic across octets tripped me up a bit.

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AI HintsAI Generated

Suggested Approach

Clarify the input format (string vs. integer) and edge cases like overflow/underflow, then propose converting the IP to a 32-bit integer, performing the increment/decrement, and converting back. Discuss trade-offs between string manipulation and integer conversion, and handle boundary conditions explicitly.

Pro tip: Mention that you would treat the IP as an unsigned 32-bit integer to simplify arithmetic, but also discuss how to handle overflow/underflow gracefully (e.g., wrapping or returning an error) based on requirements. This shows awareness of real-world constraints.

1. Clarify requirements and edge cases

Ask about input format (string or integer), expected behavior at boundaries (0.0.0.0 and 255.255.255.255), and whether wrapping or error is preferred. Confirm if the function should handle both next and previous.

2. Choose representation

Decide between string manipulation (splitting octets) and integer conversion. Explain that integer conversion simplifies arithmetic and is less error-prone for carries/borrows.

3. Implement conversion and arithmetic

Convert IP string to 32-bit integer (e.g., using bit shifts), add or subtract 1, and convert back to dotted-decimal string. Handle overflow/underflow by either wrapping or throwing an error.

4. Test and validate

Walk through test cases: normal increment (e.g., 192.168.1.1 -> 192.168.1.2), carry across octets (192.168.1.255 -> 192.168.2.0), boundaries (0.0.0.0 and 255.255.255.255), and invalid inputs.

5. Discuss trade-offs and optimizations

Compare integer vs. string approach in terms of performance, readability, and edge-case handling. Mention potential optimizations like bitwise operations or avoiding string conversions if the IP is already an integer.

Key Points to Mention

  • Input validation: ensure the IP string is well-formed and within valid range.
  • Integer conversion: use bitwise operations (e.g., (a << 24) | (b << 16) | (c << 8) | d) for efficiency.
  • Boundary handling: define behavior for 0.0.0.0 (decrement) and 255.255.255.255 (increment) — wrap or error.
  • Carry/borrow logic: integer arithmetic automatically handles carries across octets, unlike naive string manipulation.
  • Time and space complexity: O(1) for integer approach, O(n) for string parsing but n is small (max 15 chars).
  • Testing: include edge cases like 0.0.0.0, 255.255.255.255, and addresses with leading zeros (if allowed).

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