In-Memory File System

Question

Implement an in-memory Unix-style file system. Reported as a multi-part, hands-on coding round (often described as LeetCode 588 'lightly modified'): Part 1 — mkdir, touch, ls; Part 2 — rm, rmdir; Part 3 — cd. A common variant feeds raw command-line strings ("mkdir /a", "touch /a/f") that you must parse and execute, backed by a tree/trie of nodes with path parsing; one report also lists reading, writing, and searching. Candidates consistently report that the design isn't exotic, but writing it from scratch and debugging one stubborn edge case inside the time box — with little interviewer help — is what fails people.

AceOffer · Accepted Answer

Implement an in-memory Unix-style file system. Reported as a multi-part, hands-on coding round (often described as LeetCode 588 'lightly modified'): Part 1 — mkdir, touch, ls; Part 2 — rm, rmdir; Part 3 — cd. A common variant feeds raw command-line strings ("mkdir /a", "touch /a/f") that you must parse and execute, backed by a tree/trie of nodes with path parsing; one report also lists reading, writing, and searching. Candidates consistently report that the design isn't exotic, but writing it from scratch and debugging one stubborn edge case inside the time box — with little interviewer help — is what fails people.

Reported follow-ups:
1. A common variant hands you raw command-line strings to parse and execute rather than calling methods directly. (when: mid-problem)
2. Support cd and relative paths, so subsequent commands resolve against a current working directory. (when: after Parts 1-2 pass)
3. Should mkdir behave like 'mkdir' (parent must exist) or 'mkdir -p' (create intermediate directories)? (when: clarifying scope)

**Common mistakes:** conflating files and directories (ls/rm/rmdir behave differently on each); rmdir silently succeeding on a non-empty directory; path parsing that ignores '.', '..', trailing slashes, or absolute-vs-relative. **Approach:** build and unit-test the path resolver first so a bug is localized to one small function.

In-Memory File System

Problem Overview

Follow-up Arc

What Reports Emphasize

Practice

Every question in the Perplexity catalog gets this depth