<h2><a href="https://leetcode.com/problems/longest-palindrome/">409. Longest Palindrome</a></h2><h3>Easy</h3><hr><div><p>Given a string <code>s</code> which consists of lowercase or uppercase letters, return the length of the <strong>longest <span data-keyword="palindrome-string">palindrome</span></strong>&nbsp;that can be built with those letters.</p>

<p>Letters are <strong>case sensitive</strong>, for example, <code>"Aa"</code> is not considered a palindrome.</p>

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

<pre><strong>Input:</strong> s = "abccccdd"
<strong>Output:</strong> 7
<strong>Explanation:</strong> One longest palindrome that can be built is "dccaccd", whose length is 7.
</pre>

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

<pre><strong>Input:</strong> s = "a"
<strong>Output:</strong> 1
<strong>Explanation:</strong> The longest palindrome that can be built is "a", whose length is 1.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 2000</code></li>
	<li><code>s</code> consists of lowercase <strong>and/or</strong> uppercase English&nbsp;letters only.</li>
</ul>
</div>