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Implement an In-Memory File System

eBaySoftware Engineer · Online Assessment
MediumSoftware EngineerOnline AssessmentCoding & Algorithms

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This problem tests proficiency with hierarchical data structures (trees/tries) and object-oriented design by requiring the implementation of an in-memory file system with file/directory management and path resolution.

Problem Statement

Design an in-memory file system that supports basic file and directory operations. Your system should be represented as a tree structure where each node is either a file or a directory.

API Requirements

  • void mkdir(string path): Create a new directory at the given path. The parent directories must exist.
  • void addContentToFile(string filePath, string content): If the file does not exist, create it and append the content. If it exists, append the content.
  • string readContentFromFile(string filePath): Return the content of the file at the given path.
  • List ls(string path): If the path is a file, return a list containing only the file name. If it is a directory, return a sorted list of names of the files and directories in that path.

Constraints

  • Paths are absolute and start with '/'.
  • Directory names and file names contain only lowercase English letters.
  • The root directory '/' is always present.

Examples

// Example 1:
fs.mkdir("/a/b/c");
fs.addContentToFile("/a/b/c/d", "hello");
fs.ls("/a/b/c"); // returns ["d"]
fs.readContentFromFile("/a/b/c/d"); // returns "hello"

// Example 2:
fs.ls("/"); // returns ["a"]

Edge Cases

  • Accessing paths that don't exist.
  • Performing operations on the root directory.
  • Adding content to a directory path instead of a file.

Hints

Hint 1

Use a Trie-like data structure where each node represents either a file or a directory and contains a map to its children.

Hint 2

Store the content in the file-type nodes and a boolean flag to distinguish between files and directories.

Hint 3

Split the path string by '/' to traverse the tree level by level until you reach the target node.

Follow-up questions

  • How would you modify this system to support 'rm' (removing files or directories recursively)?
  • How would you implement file permissions (e.g., read, write, execute) for different users?
  • If the file system needed to be persistent, how would you approach serializing the tree structure to disk?