Design a File System (Hash Map and Set)
Design a simplified file system that supports two operations: `addPath` (to create a directory/file path) and `get` (to retrieve a value associated with the path). Use a Hash Map to store paths and values.
Why Interviewers Ask This
Amazon asks this question to evaluate a candidate's ability to select appropriate data structures for specific constraints and to demonstrate clear communication of trade-offs. They are testing if you can efficiently handle path-based lookups while managing memory, ensuring the solution scales logically without unnecessary complexity.
How to Answer This Question
1. Clarify requirements: Ask if paths are case-sensitive, if duplicates overwrite values, and how deeply nested paths should be handled. 2. Propose the core structure: Suggest using a Hash Map where keys are full file paths (strings) and values are the associated data, noting O(1) average time complexity for both insertion and retrieval. 3. Discuss edge cases: Address invalid inputs like null paths, empty strings, or attempts to add paths that already exist. 4. Consider scalability: Briefly mention that while a Hash Map is efficient, a Trie might be better if prefix searches were required, but stick to the Hash Map as requested. 5. Implement and walk through code: Write clean pseudocode or actual code, explaining variable names and logic flow clearly to Amazon's leadership principles of 'Dive Deep' and 'Deliver Results'.
Key Points to Cover
- Selecting a Hash Map provides O(1) average time complexity for both add and get operations.
- Using the full path string as the unique key simplifies the logic compared to tree traversal.
- Handling edge cases like null inputs or duplicate paths shows attention to detail.
- Explaining why a Hash Map is chosen over a Trie demonstrates architectural decision-making skills.
- Writing clean, readable code reflects Amazon's expectation for maintainable and scalable solutions.
Sample Answer
To design this simplified file system, I will start by clarifying the requirements. We need an `addPath` method to store a value at a specific string path and a `get` method to retrieve it. Since we only need exact match…
Common Mistakes to Avoid
- Overcomplicating the design by implementing a Trie when the requirement only asks for exact path matching.
- Failing to validate input parameters, leading to potential runtime errors with null or empty strings.
- Ignoring the scenario where a path already exists and deciding arbitrarily whether to overwrite or reject.
- Not discussing time and space complexity, missing the opportunity to show analytical depth.
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