In-Memory Unix-Style File System

Coding — Software Engineer

Problem Overview

Build a Unix-inspired file system that exists entirely in memory. The interview format presents this as a two-stage implementation task, with command-style APIs resembling a standard in-memory file-system design exercise.

Create a class that works with absolute paths, including /, /var, and /var/log.txt.

class InMemoryUnixFileSystem:
    def touch(self, path: str) -> None:
        """Create an empty file if it does not already exist."""

    def mkdir(self, path: str) -> None:
        """Create a directory."""

    def ls(self, path: str) -> list[str]:
        """List a directory, or return the file name if path is a file."""

    def rm(self, path: str) -> bool:
        """Remove a file. Return True if a file was removed."""

    def rmdir(self, path: str) -> bool:
        """Remove an empty directory. Return True if a directory was removed."""

Clarifications

• Every path is absolute, meaning it starts with /.
• Repeated / characters and a final / should be normalized; for example, /x///y/ represents the same location as /x/y.
• mkdir(path) has mkdir -p semantics, so it creates any absent directories along the route.
• touch(path) may add a file only when its parent directory is already present.
• Within one parent directory, a file and a directory may not use the same name.
• Calling ls("/") produces the root directory's child names in lexicographical order.
• Calling ls on a file returns a list containing only that file's name.
• rm(path) is limited to file deletion and must not delete a directory.
• rmdir(path) succeeds only for empty directories; it must reject both / and directories that still contain entries.
• touch("/") is not allowed, since / identifies the root directory rather than a file.

fs = InMemoryUnixFileSystem()

fs.mkdir("/projects/api")
fs.touch("/projects/api/main.py")
fs.touch("/projects/NOTES.txt")

fs.ls("/") # ["projects"]
fs.ls("/projects") # ["NOTES.txt", "api"]
fs.ls("/projects/api") # ["main.py"]
fs.ls("/projects/api/main.py") # ["main.py"]

fs.rm("/projects/api/main.py") # True
fs.ls("/projects/api") # []

fs.rmdir("/projects/api") # True
fs.ls("/projects") # ["NOTES.txt"]

fs.rmdir("/projects") # False, NOTES.txt still exists inside it
fs.rm("/projects") # False, this path names a directory
fs.rm("/projects/NOTES.txt") # True
fs.rmdir("/projects") # True

Starter Code

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