Anthropic·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Apr 2026Remote

Summary

Anthropic coding interview that was more systems-thinking than I expected. The problem looked like a straightforward image processing exercise but they really wanted to see how you design a clean API and reason about trade-offs, not just grind out the pixel math.

Questions Asked (1)

Implement a set of image processing operations on a 2D pixel grid (box blur with a configurable kernel, horizontal and vertical flip, 90-degree rotation, brightness adjustment). Define a clean interface so operations can be chained or composed, and walk through the trade-offs between in-place and out-of-place execution.

System DesignTechnical Trade-offsAlgorithms & Data Structures

Author's notes

I jumped straight into writing the individual functions before thinking about the interface, which was the wrong move.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements (e.g., image format, performance constraints) and then define a clean interface for image operations, such as an abstract class or protocol with an apply method. Discuss the trade-offs between in-place and out-of-place execution, considering memory, performance, and composability, and illustrate with examples of chaining operations.

Pro tip: Emphasize that in-place operations can be more memory-efficient but may complicate chaining and introduce aliasing bugs, while out-of-place operations are safer and enable parallelization but require more memory. Mention that a hybrid approach or copy-on-write can balance these concerns.

1. Clarify Requirements and Constraints

Ask about image size, performance needs, memory limits, and whether operations need to be reversible or composable. This shows you consider the context before diving into design.

2. Define a Clean Interface

Propose an interface (e.g., ImageOperation with a method apply(Image) -> Image) that allows operations to be chained or composed. Discuss how this enables a pipeline pattern.

3. Discuss Implementation Details

Briefly outline how each operation (box blur, flip, rotate, brightness) could be implemented, focusing on algorithmic complexity and edge cases (e.g., kernel size, boundary handling).

4. Analyze In-Place vs. Out-of-Place Trade-offs

Compare memory usage, performance (cache locality, allocation overhead), safety (aliasing, thread-safety), and composability. Give examples of when each is preferable.

5. Propose a Design and Summarize

Recommend a design that balances the trade-offs, possibly allowing both modes or using immutable images. Summarize key points and invite feedback.

Key Points to Mention

Interface design: abstract class or protocol with apply method, enabling chaining via method chaining or pipeline.
In-place pros: lower memory footprint, better cache performance; cons: mutates input, harder to debug, not thread-safe.
Out-of-place pros: immutability, easier to reason about, thread-safe; cons: higher memory usage, allocation overhead.
Composability: out-of-place naturally supports chaining; in-place may require careful ordering or copies.
Performance considerations: box blur complexity O(n*k^2) or separable O(n*k), use of separable filters.
Edge cases: boundary handling for blur, rotation dimensions, brightness clamping.

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