In-Memory File System

Design and implement a simple in-memory file system that supports the following operations:

• mkdir(path: str): Create a directory at the specified path.
• addContentToFile(path: str, content: str): Append content to a file at the specified path. If the file does not exist, create it.
• readContentFromFile(path: str): Return the content of the file.
• ls(path: str): If path is a file, return a list containing only the file's name; if it is a directory, return the list of files and subdirectories in lexicographical order.

The file system path follows a Unix-like format with '/' as the directory separator. In mathematical terms, a valid path can be represented as: \( path = '/'(\text{dir}/)* (\text{file})? \).

Your solution should process input via stdin and produce output on stdout as described in the input/output sections.

inputFormat

The input is provided via stdin. The first line contains an integer N representing the number of operations. Each of the next N lines contains one operation command in one of the following formats:

• mkdir <path>
• add <path> "<content>" (the content is enclosed in double quotes)
• read <path>
• ls <path>

Note: For operations that output a result (i.e. read and ls), each output should be printed on a separate line in the order the operations occur.

outputFormat

For each read or ls operation, output the result on a separate line to stdout. For a read command, print the content of the file. For a ls command, print the names (sorted lexicographically if it is a directory) separated by a single space.

## sample

6
mkdir /a/b/c
add /a/b/c/d "hello"
read /a/b/c/d
add /a/b/c/d " world"
read /a/b/c/d
ls /a/b/c

hello
hello world
d

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