count-substrings-with-k-frequency-characters-i

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Algorithms

Given a string <code>s</code> and an integer <code>k</code>, return the total number of substrings of <code>s</code> where at least one character appears at least <code>k</code> times.

&nbsp;
Example 1:

<div class="example-block">
Input: s = &quot;abacb&quot;, k = 2

Output: 4

Explanation:

The valid substrings are:

<ul>
	<li><code>&quot;aba&quot;</code> (character <code>&#39;a&#39;</code> appears 2 times).</li>
	<li><code>&quot;abac&quot;</code> (character <code>&#39;a&#39;</code> appears 2 times).</li>
	<li><code>&quot;abacb&quot;</code> (character <code>&#39;a&#39;</code> appears 2 times).</li>
	<li><code>&quot;bacb&quot;</code> (character <code>&#39;b&#39;</code> appears 2 times).</li>
</ul>
</div>

Example 2:

<div class="example-block">
Input: s = &quot;abcde&quot;, k = 1

Output: 15

Explanation:

All substrings are valid because every character appears at least once.
</div>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= s.length &lt;= 3000</code></li>
	<li><code>1 &lt;= k &lt;= s.length</code></li>
	<li><code>s</code> consists only of lowercase English letters.</li>
</ul>