Formatted question description:

1233. Remove Sub-Folders from the Filesystem




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”]


  • 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.


Create a class Folder that contains the current folder’s name and a list of its children, which also have type Folder.

Sort the array folder. Use a list to store the root folders that are objects of type Folder. For each folderName in folder, if the list is empty, create a new folder using folderName and add it to the list. Otherwise, loop over existing roots and try to add a subfolder. If a subfolder is added successfully, then it is a subfolder. Otherwise, create a new folder as a root folder and add it to the list.

Finally, loop over the list and add the roots’ names to the result list and return.

  • class Solution {
        public List<String> removeSubfolders(String[] folder) {
            List<Folder> roots = new ArrayList<Folder>();
            for (String folderName : folder) {
                if (roots.isEmpty()) {
                    Folder newFolder = new Folder(folderName);
                } else {
                    boolean flag = false;
                    for (Folder root : roots) {
                        boolean addSubfolder = addSubfolder(root, folderName);
                        if (addSubfolder) {
                            flag = true;
                    if (!flag) {
                        Folder newFolder = new Folder(folderName);
            List<String> remainingFolders = new ArrayList<String>();
            for (Folder root : roots) {
                String rootName = root.folderName;
            return remainingFolders;
        public boolean addSubfolder(Folder root, String folderName) {
            String rootName = root.folderName;
            if (!folderName.contains(rootName))
                return false;
            String[] rootNameArray = rootName.split("/");
            String[] folderNameArray = folderName.split("/");
            if (rootNameArray.length == folderNameArray.length)
                return false;
            else {
                return true;
    class Folder {
        String folderName;
        List<Folder> children;
        public Folder() {
        public Folder(String folderName) {
            this.folderName = folderName;
            children = new ArrayList<Folder>();
        public void addSubfolder(String subFolderName) {
            Folder subFolder = new Folder(subFolderName);
  • // OJ:
    // Time: O(NlogN * W)
    // Space: O(NW)
    struct Node {
        unordered_map<string, Node*> m;
        bool end = false;
    class Solution {
        vector<string> removeSubfolders(vector<string>& A) {
            Node root;
            sort(begin(A), end(A));
            vector<string> ans;
            for (auto &s : A) {
                string word;
                istringstream ss(s);
                auto node = &root;
                bool skip = false;
                while (getline(ss, word, '/') && !skip) {
                    if (word.empty()) continue;
                    if (node->m.count(word) && node->m[word]->end) skip = true;
                    if (!node->m[word]) node->m[word] = new Node();
                    node = node->m[word];
                if (skip) continue;
                node->end = true;
            return ans;
  • # 1233. Remove Sub-Folders from the Filesystem
    class Solution:
        def removeSubfolders(self, folder: List[str]) -> List[str]:
            folder.sort(key = len)
            s = set()
            res = []
            for f in folder:
                path = f.split("/")[1:]
                full = ""
                for p in path:
                    full += p
                    if full in s: break
            return res

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