<h2><a href="https://leetcode.com/problems/remove-sub-folders-from-the-filesystem/">1233. Remove Sub-Folders from the Filesystem</a></h2><h3>Medium</h3><hr><div><p>Given a list of folders <code>folder</code>, return <em>the folders after removing all <strong>sub-folders</strong> in those folders</em>. You may return the answer in <strong>any order</strong>.</p>

<p>If a <code>folder[i]</code> is located within another <code>folder[j]</code>, it is called a <strong>sub-folder</strong> of it. A sub-folder of <code>folder[j]</code> must start with <code>folder[j]</code>, followed by a <code>"/"</code>. For example, <code>"/a/b"</code> is a sub-folder of <code>"/a"</code>, but <code>"/b"</code> is not a sub-folder of <code>"/a/b/c"</code>.</p>

<p>The format of a path is one or more concatenated strings of the form: <code>'/'</code> followed by one or more lowercase English letters.</p>

<ul>

<li>For example, <code>"/leetcode"</code> and <code>"/leetcode/problems"</code> are valid paths while an empty string and <code>"/"</code> are not.</li>

</ul>

<p>&nbsp;</p>

<p><strong class="example">Example 1:</strong></p>

<pre><strong>Input:</strong> folder = ["/a","/a/b","/c/d","/c/d/e","/c/f"]

<strong>Output:</strong> ["/a","/c/d","/c/f"]

<strong>Explanation:</strong> Folders "/a/b" is a subfolder of "/a" and "/c/d/e" is inside of folder "/c/d" in our filesystem.

</pre>

<p><strong class="example">Example 2:</strong></p>

<pre><strong>Input:</strong> folder = ["/a","/a/b/c","/a/b/d"]

<strong>Output:</strong> ["/a"]

<strong>Explanation:</strong> Folders "/a/b/c" and "/a/b/d" will be removed because they are subfolders of "/a".

</pre>

<p><strong class="example">Example 3:</strong></p>

<pre><strong>Input:</strong> folder = ["/a/b/c","/a/b/ca","/a/b/d"]

<strong>Output:</strong> ["/a/b/c","/a/b/ca","/a/b/d"]

</pre>

<p>&nbsp;</p>

<p><strong>Constraints:</strong></p>

<ul>

<li><code>1 &lt;= folder.length &lt;= 4 * 10⁴</code></li>

<li><code>2 &lt;= folder[i].length &lt;= 100</code></li>

<li><code>folder[i]</code> contains only lowercase letters and <code>'/'</code>.</li>

<li><code>folder[i]</code> always starts with the character <code>'/'</code>.</li>

<li>Each folder name is <strong>unique</strong>.</li>

</ul>

</div>