Anthropic·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Jul 2026Remote

Summary

Coding round at Anthropic for a software engineer role, centered entirely on one problem with five escalating parts. The core concept was straightforward but the edge cases kept piling up in ways I didn't fully anticipate going in.

Questions Asked (1)

Implement an IP address iterator class that takes a starting IPv4 address and a step size as constructor arguments, then yields successive addresses by advancing that step each time. The class should include next() and hasNext() methods and correctly handle overflow across octets, wrap-around, very large steps, and both string and integer representations.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The first part felt easy and I got comfortable fast, which was a mistake.

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AI HintsAI Generated

Suggested Approach

Clarify requirements and edge cases first, then design the class using a 32-bit unsigned integer for the current address and step to simplify arithmetic. Implement next() and hasNext() with modular arithmetic to handle overflow and wrap-around, and provide methods to get both string and integer representations.

Pro tip: Proactively discuss the trade-offs between using a 32-bit integer versus an array of octets, and mention how you would test edge cases like maximum step size and wrap-around to demonstrate thoroughness.

1. Clarify Requirements and Edge Cases

Ask about the expected behavior for wrap-around (e.g., should it stop or cycle?), the maximum step size, and whether the iterator should be infinite. Confirm that both string and integer representations are needed.

2. Choose Data Representation

Decide between storing the address as a 32-bit unsigned integer or as four octets. Using a 32-bit integer simplifies arithmetic and overflow handling, but you should be prepared to discuss the trade-offs.

3. Design the Class Interface

Define the constructor to accept a starting IPv4 address (as string or integer) and a step size. Implement next() to return the next address and advance the current address, and hasNext() to indicate if another address is available (considering wrap-around policy).

4. Implement Arithmetic and Overflow Handling

Use modular arithmetic (mod 2^32) to handle overflow across octets and wrap-around. Ensure that large steps are handled correctly by adding the step modulo 2^32.

5. Provide String and Integer Representations

Implement methods to convert the internal integer representation to a dotted-decimal string and to return the integer value. Ensure conversions are correct and efficient.

Key Points to Mention

Use of 32-bit unsigned integer for address and step to simplify arithmetic and overflow handling.
Modular arithmetic (mod 2^32) to handle wrap-around and large steps.
Conversion between string (dotted-decimal) and integer representations.
Edge cases: maximum step size, wrap-around behavior, and invalid input handling.
Trade-offs between different data representations (integer vs. octet array).
Testing strategy: unit tests for overflow, wrap-around, and large steps.

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