【leetcode】1233. Remove Sub-Folders from the Filesystem

题目如下：

Given a list of folders, remove all sub-folders in those folders and return in any order the folders after removing.

If a folder[i] is located within another folder[j], it is called a sub-folder of it.

The format of a path is one or more concatenated strings of the form: / followed by one or more lowercase English letters. For example, /leetcode and /leetcode/problems are valid paths while an empty string and / are not.

Example 1:

Input: folder = ["/a","/a/b","/c/d","/c/d/e","/c/f"]
Output: ["/a","/c/d","/c/f"]
Explanation: Folders "/a/b/" is a subfolder of "/a" and "/c/d/e" is inside of folder "/c/d" in our filesystem.

Example 2:

Input: folder = ["/a","/a/b/c","/a/b/d"]
Output: ["/a"]
Explanation: Folders "/a/b/c" and "/a/b/d/" will be removed because they are subfolders of "/a".

Example 3:

Input: folder = ["/a/b/c","/a/b/ca","/a/b/d"]
Output: ["/a/b/c","/a/b/ca","/a/b/d"]

Constraints:

• 1 <= folder.length <= 4 * 10^4
• 2 <= folder[i].length <= 100
• folder[i] contains only lowercase letters and '/'
• folder[i] always starts with character '/'
• Each folder name is unique.

解题思路：首先建立字典树，并把folder按元素从短到长排好序，然后遍历folder，并与字典树中已有元素做前缀匹配。如果folder[i]存在于字典树中，表示是其他目录的子目录，删除；如果不存在，则把该目录插入到字典树中。

代码如下：

class TreeNode(object):
    def __init__(self, x):
        self.val = x
        self.childDir = {}
        self.isDir = False

class Trie(object):
    dic = {}
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.root = TreeNode(None)
        self.dic = {}

    def insert(self,word):
        node = self.root
        for i in word:
            if i not in node.childDir:
                node.childDir[i] = TreeNode(i)
            node = node.childDir[i]
        node.isDir = True

    def isDelete(self,dir):
        node = self.root
        for i in dir:
            if i in node.childDir:
                node = node.childDir[i]
                if node.isDir == True:
                    return True
            else:
                return False
        return False

class Solution(object):
    def removeSubfolders(self, folder):
        """
        :type folder: List[str]
        :rtype: List[str]
        """
        folder.sort(cmp=lambda x1,x2:len(x1) - len(x2))
        trie = Trie()
        res = []
        for f in folder:
            if trie.isDelete(f) == False:
                res.append(f)
                trie.insert(f + '/')
        return res