TikTok 面试真题解析：设计内存文件系统（In-Memory File System）｜路径结构与数据结构设计题

Design a data structure that simulates an in-memory file system.

Implement the FileSystem class:

• FileSystem() Initializes the object of the system
• List<String> ls(String path)
  • Returns the list of directory names in this directory. The answer should be in lexicographic order.
• void mkdir(String path)
  • Makes a new directory according to the given path. If the middle directories in the path do not exist, you should create them as well.

Example:FileSystem fileSystem = new FileSystem();
fileSystem.ls("/");        // return []
fileSystem.mkdir("/a/b/c");
fileSystem.ls("/");        // return ["a"]

这道题重点考察数据结构设计能力，而不是算法复杂度。文件系统本质是一个树结构，每一层路径都是一个节点。mkdir 需要按路径逐层创建节点，缺失的中间目录也要自动补齐；ls 则需要返回当前节点下的子目录，并按字典序排序。难点在于路径解析和结构组织是否清晰，而不是计算本身。