design-in-memory-file-system.py

# Time:  ls: O(l + klogk), l is the path length, k is the number of entries in the last level directory
#        mkdir: O(l)
#        addContentToFile: O(l + c), c is the content size
#        readContentFromFile: O(l + c)
# Space: O(n + s), n is the number of dir/file nodes, s is the total content size.

# Design an in-memory file system to simulate the following functions:
#
# ls: Given a path in string format. If it is a file path,
#     return a list that only contains this file's name.
#     If it is a directory path, return the list of file and directory names in this directory.
#     Your output (file and directory names together) should in lexicographic order.
#
# mkdir: Given a directory path that does not exist,
#       you should make a new directory according to the path.
#       If the middle directories in the path don't exist either,
#       you should create them as well. This function has void return type.
#
# addContentToFile: Given a file path and file content in string format.
#                   If the file doesn't exist, you need to create that file containing given content.
#                   If the file already exists, you need to append given content to original content.
#                   This function has void return type.
#
# readContentFromFile: Given a file path, return its content in string format.
#
# Example:
# Input: 
# ["FileSystem","ls","mkdir","addContentToFile","ls","readContentFromFile"]
# [[],["/"],["/a/b/c"],["/a/b/c/d","hello"],["/"],["/a/b/c/d"]]
# Output:
# [null,[],null,null,["a"],"hello"]
#
# Note:
# 1. You can assume all file or directory paths are absolute paths
#   which begin with / and do not end with / except that the path is just "/".
# 2. You can assume that all operations will be passed valid parameters and
#   users will not attempt to retrieve file content or list a directory or file that does not exist.
# 3. You can assume that all directory names and file names only contain lower-case letters,
#   and same names won't exist in the same directory.
   

class TrieNode(object):
    
    def __init__(self):
        self.is_file = False
        self.children = {}
        self.content = ""

class FileSystem(object):

    def __init__(self):
        self.__root = TrieNode()
        

    def ls(self, path):
        """
        :type path: str
        :rtype: List[str]
        """
        curr = self.__getNode(path)
        
        if curr.is_file:
            return [self.__split(path, '/')[-1]]

        return sorted(curr.children.keys()) 


    def mkdir(self, path):
        """
        :type path: str
        :rtype: void
        """
        curr = self.__putNode(path)
        curr.is_file = False
        

    def addContentToFile(self, filePath, content):
        """
        :type filePath: str
        :type content: str
        :rtype: void
        """
        curr = self.__putNode(filePath)
        curr.is_file = True
        curr.content += content


    def readContentFromFile(self, filePath):
        """
        :type filePath: str
        :rtype: str
        """
        return self.__getNode(filePath).content


    def __getNode(self, path):
        curr = self.__root
        for s in self.__split(path, '/'):
            curr = curr.children[s]
        return curr


    def __putNode(self, path):
        curr = self.__root
        for s in self.__split(path, '/'):
            if s not in curr.children:
                curr.children[s] = TrieNode()
            curr = curr.children[s]
        return curr


    def __split(self, path, delim):
        if path == '/':
            return []
        return path.split('/')[1:]

# Your FileSystem object will be instantiated and called as such:
# obj = FileSystem()
# param_1 = obj.ls(path)
# obj.mkdir(path)
# obj.addContentToFile(filePath,content)
# param_4 = obj.readContentFromFile(filePath)