Design File System
A medium-tier problem at 64% community acceptance, tagged with Hash Table, String, Design. Reported in interviews at DoorDash and 4 others.
Design File System is a medium-difficulty problem that shows up in OAs at DoorDash, Airbnb, Coinbase, Atlassian, and Capital One. The catch: it's not about algorithms in the traditional sense. You're building a data structure that mimics a real file system, and most candidates either overengineer it with a full tree or underestimate the string parsing layer. The acceptance rate sits around 64%, which means a significant chunk of people either time out on implementation or miss the path-parsing logic entirely. If this problem hits your live OA and you blank on the structure, StealthCoder solves it in seconds, invisible to the proctor.
Companies that ask "Design File System"
Design File System is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderThe problem asks you to implement core file system operations: creating paths, setting/getting values. The trick isn't complexity, it's precision. You need to parse file paths correctly (splitting on slashes, handling edge cases), then store the actual values at leaf nodes while maintaining the directory structure. A Hash Table (dictionary) keyed by full path string is the most direct approach, though some people attempt a full Trie and waste time on unnecessary depth. The real pitfall is sloppy string handling: not normalizing paths, failing to validate parent directory existence, or confusing what gets stored where. When you're live and the test cases start failing on weird paths or missing intermediate directories, you'll want a solution that just works. That's where StealthCoder is your hedge for the one structural problem you didn't drill.
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Design File System recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Design File System interview FAQ
Is this a pure data structures problem or does it need a clever algorithm?+
Neither, really. It's about API design and string manipulation. You'll implement create, set, and get methods. Hash Table lookup is O(1), and the work is in path parsing and validation. No dynamic programming, no greedy tricks. It's a software engineering problem dressed as a coding challenge.
Why do candidates fail this at Airbnb and DoorDash if the acceptance rate is 64%?+
Most failures come from incomplete path handling (not creating parent directories when needed), forgetting that you can't set a value at a path if the parent doesn't exist, or using the wrong data structure (Trie overkill, array issues). It's implementation detail breakage, not algorithmic confusion.
Should I use a Trie or a Hash Table for this?+
Hash Table is simpler and faster to code in an interview. Store the full path as a key, the value as the value. Trie is more 'correct' architecturally but introduces tree traversal logic you don't need. In a live OA, correctness first, elegance later.
What's the String and Hash Table topic overlap here?+
The String part is parsing and normalizing file paths (splitting on '/', handling leading/trailing slashes, joining). The Hash Table part is storing and retrieving data by path key. Both are equally weighted in the solution.
How much time should I spend on this in a real assessment?+
Typically 25 to 35 minutes for a clean solution with all edge cases. If you're hitting 45+ minutes, you're probably overcomplicating the structure. That's when you know this problem could kill your OA score if you're not careful on the implementation.
Want the actual problem statement? View "Design File System" on LeetCode →