Anthropic·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

May 2026Remote

Summary

Anthropic SWE interview with a filesystem path resolution problem that looked manageable at first glance but has enough edge cases to chew through your whole session if you're not careful. Symlink cycle detection was the part that tripped me up.

Questions Asked (1)

Implement a Unix-style `cd` path resolver that handles absolute and relative paths, dot components, symbolic links, and cycle detection, returning the final canonical path or "CYCLE" if a link loop is encountered.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs

Author's notes

The basic path normalization part (splitting on `/`, handling `.` and `..`) came together pretty fast.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and assumptions, then design a step-by-step algorithm that processes path components, resolves symbolic links iteratively, and detects cycles using a visited set. Implement the solution with careful handling of edge cases and test thoroughly.

Pro tip: Explicitly state your assumptions about the filesystem model (e.g., symlink targets are absolute or relative to the link's directory) and discuss how you would handle cycles—this shows you think about real-world edge cases and system design trade-offs.

1. Clarify requirements and assumptions

Ask about the filesystem representation (e.g., map of paths to targets), symlink resolution rules, and expected behavior for non-existent paths. Confirm that 'CYCLE' is returned only for symlink loops.

2. Design the algorithm

Outline a component-based approach: start with the base path (absolute or current directory), split the input path into components, and process each component while maintaining a stack of resolved directories. For symlinks, recursively resolve the target and detect cycles.

3. Handle symbolic links and cycles

When encountering a symlink, resolve its target relative to the symlink's directory, then continue processing the remaining components. Use a set of visited symlink paths (or a depth limit) to detect cycles and return 'CYCLE' if a loop is found.

4. Implement and test

Write clean code with helper functions for path normalization and symlink resolution. Test with cases: absolute/relative paths, '.', '..', multiple symlinks, and cycles. Walk through an example to verify correctness.

5. Analyze complexity and trade-offs

Discuss time and space complexity (O(n) where n is path length, with cycle detection using O(k) space for k symlinks). Mention alternative approaches like iterative resolution with a queue and trade-offs between recursion depth and explicit stack.

Key Points to Mention

Path normalization: handling '.', '..', and redundant slashes
Symlink resolution: resolving targets relative to the symlink's directory
Cycle detection: using a visited set or depth limit to avoid infinite loops
Edge cases: non-existent paths, symlinks to directories, and absolute vs relative symlink targets
Complexity analysis: time and space complexity of the algorithm
Testing strategy: unit tests for various path scenarios and cycle cases

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