System Design — In-Memory File System

Model a tiny file system as a tree of directories and files.

solve(args, ops) builds new FileSystem() (an empty root /) and replays ops. Paths are
absolute, start with / and use / as the separator; names contain no slash.

• ls(path) — if path is a directory, return the names of its entries (files and

directories) in lexicographic order; if it is a file, return an array holding just the
file's name.

• mkdir(path) — create the directory, including any missing parents. Nothing happens if it

already exists. Returns nothing.

• addcontent(path, content) — create the file if needed (with any missing parent directories)

and append content to it. Returns nothing.

• read(path) — return the full content of the file.

Only valid operations are tested (no listing of a missing path, no reading a directory).

Example

ls("/") → []    mkdir("/a/b/c")    addcontent("/a/b/c/d","hello")    ls("/") → ["a"]
read("/a/b/c/d") → "hello"    ls("/a/b/c/d") → ["d"]    ls("/a/b/c") → ["d"]