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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/d","/a/b/ca"]
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.

你是一位系统管理员，手里有一份文件夹列表 folder，你的任务是要删除该列表中的所有 子文件夹，并以 任意顺序 返回剩下的文件夹。

我们这样定义「子文件夹」：

如果文件夹 folder[i] 位于另一个文件夹 folder[j] 下，那么 folder[i] 就是 folder[j] 的子文件夹。
文件夹的「路径」是由一个或多个按以下格式串联形成的字符串：

/ 后跟一个或者多个小写英文字母。
例如，/leetcode 和 /leetcode/problems 都是有效的路径，而空字符串和 / 不是。

示例 1：

输入：folder = ["/a","/a/b","/c/d","/c/d/e","/c/f"]
输出：["/a","/c/d","/c/f"]
解释："/a/b/" 是 "/a" 的子文件夹，而 "/c/d/e" 是 "/c/d" 的子文件夹。
示例 2：

输入：folder = ["/a","/a/b/c","/a/b/d"]
输出：["/a"]
解释：文件夹 "/a/b/c" 和 "/a/b/d/" 都会被删除，因为它们都是 "/a" 的子文件夹。
示例 3：

输入：folder = ["/a/b/c","/a/b/d","/a/b/ca"]
输出：["/a/b/c","/a/b/ca","/a/b/d"]
 

提示：

1 <= folder.length <= 4 * 10^4
2 <= folder[i].length <= 100
folder[i] 只包含小写字母和 /
folder[i] 总是以字符 / 起始
每个文件夹名都是唯一的