## 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"]
```

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.

## Rust Solution

``````struct Solution;
use std::collections::HashSet;

impl Solution {
fn remove_subfolders(folder: Vec<String>) -> Vec<String> {
let mut hs: HashSet<String> = HashSet::new();
for s in folder {
hs.insert(s);
}
let mut res = vec![];
for s in &hs {
if !Self::is_subfolder(&s, &hs) {
res.push(s.clone());
}
}
res
}

fn is_subfolder(s: &str, hs: &HashSet<String>) -> bool {
let n = s.len();
for i in 0..n {
if &s[i..=i] == "/" {
if hs.contains(&s[0..i]) {
return true;
}
}
}
false
}
}

#[test]
fn test() {
let folder = vec_string!["/a", "/a/b", "/c/d", "/c/d/e", "/c/f"];
let mut res = vec_string!["/a", "/c/d", "/c/f"];
let mut ans = Solution::remove_subfolders(folder);
ans.sort();
res.sort();
assert_eq!(ans, res);
let folder = vec_string!["/a", "/a/b/c", "/a/b/d"];
let mut res = vec_string!["/a"];
let mut ans = Solution::remove_subfolders(folder);
ans.sort();
res.sort();
assert_eq!(ans, res);
let folder = vec_string!["/a/b/c", "/a/b/ca", "/a/b/d"];
let mut res = vec_string!["/a/b/c", "/a/b/ca", "/a/b/d"];
let mut ans = Solution::remove_subfolders(folder);
ans.sort();
res.sort();
assert_eq!(ans, res);
}
``````

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