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Problem solution · Python

Design in Memory File System

Design in Memory File System: a Python solution using sorting and greedy selection. Learn the idea, check the complexity, and read the full code, with credit to Kamyu LeetCode Solutions.

Technique
Sorting and greedy selection
Source
Kamyu LeetCode Solutions
Length
83 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Sorting and greedy selection

For Design in Memory File System, the implementation first exposes a useful order, then scans that order while making locally justified choices.

  1. Choose the key that reveals the greedy or grouping structure.
  2. Sort the relevant records by that key.
  3. Scan in order, maintaining the invariant that makes each local choice safe.

Code notes

  • 83 lines of Python from the credited upstream file design-in-memory-file-system.py.
  • The implementation visibly relies on sequence storage.
  • No explicit loop blocks detected.

Complexity

Sorting is typically the dominant term unless the subsequent scan uses a more expensive nested operation.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from Kamyu LeetCode Solutions by kamyu104 and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeDesign in Memory File System · PythonPython
Use this to learn the idea, then write your own version.
# 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. 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:]

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