← Openai Interview Insights

Openai·Software Engineer·Technical Phone Screen·Senior

Senior
May 2026

Summary

OpenAI software engineer interview with a filesystems-flavored coding problem that had a sneaky follow-up. The core question was straightforward enough but the symlink extension is where things got interesting.

Questions Asked (2)

Q1

Implement the Unix `cd` command: given a current working directory as an absolute path and a target path (which can be absolute or relative, and may include `.`, `..`, multiple slashes, or trailing slashes), return the resulting normalized absolute path.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

I've seen path normalization come up before but usually as a throwaway utility, not the whole question.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Clarify the rules of path resolution (absolute vs relative, handling of '.', '..', multiple slashes, trailing slashes) and then implement a stack-based normalization. Walk through examples to validate edge cases before coding.

Pro tip: Mention that you would use a stack to process path components, and that you can achieve O(n) time and O(n) space. Also, discuss how to handle edge cases like '..' at root and empty paths.

1. Clarify requirements and edge cases

Ask about the expected behavior for edge cases such as '..' at root, multiple consecutive slashes, trailing slashes, and empty target path. Confirm that the result should be a normalized absolute path.

2. Choose a data structure and algorithm

Decide to use a stack (or list) to process path components. Split the combined path (current + target if relative) by '/', then iterate through components, handling '.', '..', and empty strings appropriately.

3. Implement the normalization logic

For each component: if it's '.' or empty, skip; if it's '..', pop from stack if not empty; otherwise push onto stack. Finally, join the stack with '/' and prepend '/' to form the absolute path.

4. Test with examples and edge cases

Walk through provided examples and additional edge cases (e.g., '/..' -> '/', '/a/../..' -> '/', '/a//b/' -> '/a/b') to ensure correctness. Discuss time and space complexity.

Key Points to Mention

  • Handling of absolute vs relative paths: if target starts with '/', ignore current directory; otherwise concatenate.
  • Use of stack to process path components, with O(n) time and O(n) space complexity.
  • Edge cases: '..' at root should stay at root, multiple slashes treated as single, trailing slashes ignored.
  • Normalization rules: remove '.' components, resolve '..' by popping, and ensure result starts with '/'.
  • Potential pitfalls: empty path, path with only slashes, and ensuring no trailing slash except for root.
  • Alternative approaches: using built-in functions (e.g., os.path.normpath) but discuss why manual implementation is preferred for interview.

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

Q2

Follow-up: extend the solution to handle symbolic links. Given a map of path-to-target symlink definitions, resolve symlinks transparently during path traversal. Also handle or detect symlink cycles.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs
Author's notes

This is where I started sweating a little.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

First, clarify the symlink resolution semantics: whether to resolve only the final component or any component in the path, and how to handle relative vs absolute targets. Then, design a traversal algorithm that resolves symlinks iteratively, using a visited set to detect cycles, and analyze time/space complexity.

Pro tip: Mention that symlink resolution can be done lazily during traversal to avoid unnecessary lookups, and that cycle detection should track the chain of symlinks encountered, not just the final resolved path, to catch indirect cycles.

1. Clarify requirements and assumptions

Ask whether symlinks can appear in any path component, whether targets can be relative or absolute, and whether the map is static or dynamic. Confirm that cycles should be detected and reported as errors.

2. Design the resolution algorithm

Process the path component by component. For each component, check if it is a symlink; if so, replace it with its target and restart resolution from the beginning of the path (or continue with the remaining path appended to the target).

3. Implement cycle detection

Maintain a set of visited symlink paths (or a set of resolved paths) during a single resolution. If a symlink is encountered again, a cycle exists; return an error or a sentinel value.

4. Analyze complexity and edge cases

Discuss time complexity: O(L * S) where L is path length and S is number of symlinks, or O(N) with memoization. Cover edge cases: symlink to non-existent path, symlink to directory, relative symlinks, and maximum symlink depth.

5. Optimize and discuss trade-offs

Consider memoizing resolved paths to avoid repeated work, but note that memoization may be invalid if symlinks change. Discuss iterative vs recursive resolution and stack overflow risks.

Key Points to Mention

  • Symlink resolution semantics: resolve only the final component vs any component in the path.
  • Cycle detection using a visited set of symlink paths or resolved paths.
  • Handling relative symlink targets by resolving them relative to the symlink's directory.
  • Time and space complexity analysis, including worst-case scenarios with many symlinks.
  • Edge cases: symlink to non-existent path, symlink to directory, self-referential symlinks, and maximum symlink depth.
  • Trade-offs between eager vs lazy resolution and memoization vs fresh resolution.

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