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Problem solution · Python

Delete Duplicate Folders in System

Delete Duplicate Folders in System: a Python solution using sorting and greedy selection. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Sorting and greedy selection
Source
walkccc LeetCode Solutions
Length
45 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 Delete Duplicate Folders in 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

  • 45 lines of Python from the credited upstream file 1948.py.
  • The implementation visibly relies on sequence storage, hash lookup.
  • 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 walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeDelete Duplicate Folders in System · PythonPython
Use this to learn the idea, then write your own version.
class TrieNode:  def __init__(self):    self.children: dict[str, TrieNode] = {}    self.deleted = False  class Solution:  def deleteDuplicateFolder(self, paths: list[list[str]]) -> list[list[str]]:    ans = []    root = TrieNode()    subtreeToNodes: dict[str, list[TrieNode]] = collections.defaultdict(list)     # Construct the Trie    for path in sorted(paths):      node = root      for s in path:        node = node.children.setdefault(s, TrieNode())     # For each subtree, fill in the {subtree encoding: [root]} hash table    def buildSubtreeToRoots(node: TrieNode) -> str:      subtree = '(' + ''.join(s + buildSubtreeToRoots(node.children[s])                              for s in node.children) + ')'      if subtree != '()':        subtreeToNodes[subtree].append(node)      return subtree     buildSubtreeToRoots(root)     # Mark nodes that should be deleted    for nodes in subtreeToNodes.values():      if len(nodes) > 1:        for node in nodes:          node.deleted = True     # Construct the answer array for nodes that haven't been deleted    def constructPath(node: TrieNode, path: list[str]) -> None:      for s, child in node.children.items():        if not child.deleted:          constructPath(child, path + [s])      if path:        ans.append(path)     constructPath(root, [])    return ans

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