Openai·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026Remote

Summary

Interviewed for a software engineering role at OpenAI and got a problem that looked straightforward until I actually had to think about the edge cases. The IP address traversal question was the whole session, and it exposed some gaps in how I think about integer overflow at the byte boundary.

Questions Asked (1)

Given an IPv4 address and a count, generate the next N IPv4 addresses in ascending order, handling octet rollover correctly (e.g. 1.2.3.255 becomes 1.2.4.0).

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

My first instinct was to split on dots and manually carry the overflow across octets, which works but the code got messy fast.

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AI HintsAI Generated

Suggested Approach

Clarify input format and constraints, then convert the IPv4 address to a 32-bit integer, add the count, and convert back to dotted-decimal. Handle edge cases like overflow beyond 255.255.255.255 and ensure the output is in ascending order.

Pro tip: Mention that using integer arithmetic avoids per-octet rollover logic and is more efficient and less error-prone. Also, discuss how to handle the case where the count exceeds the remaining address space.

1. Clarify requirements and constraints

Ask about input format (string or array), whether the count can be negative, and what to do if the range exceeds the maximum IPv4 address. Confirm output format (list of strings).

2. Convert IP to integer

Parse the IPv4 address into four octets and combine them into a 32-bit unsigned integer using bitwise shifts or multiplication.

3. Generate next N addresses

Increment the integer by 1 for each address, checking for overflow beyond 2^32-1. Collect the results or convert back to dotted-decimal on the fly.

4. Convert integer back to IP

Extract each octet by shifting and masking, then format as a dotted-decimal string.

5. Handle edge cases and discuss trade-offs

Address overflow (e.g., beyond 255.255.255.255), large N, and potential performance considerations. Discuss alternative approaches like per-octet increment and their pros/cons.

Key Points to Mention

Integer representation of IPv4 addresses (32-bit unsigned integer) and conversion to/from dotted-decimal.
Handling octet rollover naturally via integer addition, avoiding per-octet carry logic.
Edge case: overflow beyond 255.255.255.255 (2^32-1) and how to handle it (e.g., throw error, wrap around, or stop).
Time and space complexity: O(N) time, O(N) space for output (or O(1) if streaming).
Alternative approach: incrementing each octet with carry propagation, and why integer arithmetic is simpler and less error-prone.
Input validation: ensuring the IP address is valid and the count is non-negative.

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