<h2><a href="https://leetcode.com/problems/longest-substring-with-at-least-k-repeating-characters/">395. Longest Substring with At Least K Repeating Characters</a></h2><h3>Medium</h3><hr><div><p>Given a string <code>s</code> and an integer <code>k</code>, return <em>the length of the longest substring of</em> <code>s</code> <em>such that the frequency of each character in this substring is greater than or equal to</em> <code>k</code>.</p>

<p data-pm-slice="1 1 []">if no such substring exists, return 0.</p>

<p>&nbsp;</p>

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

<pre><strong>Input:</strong> s = "aaabb", k = 3

<strong>Output:</strong> 3

<strong>Explanation:</strong> The longest substring is "aaa", as 'a' is repeated 3 times.

</pre>

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

<pre><strong>Input:</strong> s = "ababbc", k = 2

<strong>Output:</strong> 5

<strong>Explanation:</strong> The longest substring is "ababb", as 'a' is repeated 2 times and 'b' is repeated 3 times.

</pre>

<p>&nbsp;</p>

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

<ul>

<li><code>1 &lt;= s.length &lt;= 10⁴</code></li>

<li><code>s</code> consists of only lowercase English letters.</li>

<li><code>1 &lt;= k &lt;= 10⁵</code></li>

</ul>

</div>