Create readme : 0005-longest-palindromic-substring

Author: shimhun99

LeetCode/Medium/0005-longest-palindromic-substring/README.md

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+<h2><a href="https://leetcode.com/problems/longest-palindromic-substring">5. Longest Palindromic Substring</a></h2><h3>Medium</h3><hr><p>Given a string <code>s</code>, return <em>the longest</em> <span data-keyword="palindromic-string"><em>palindromic</em></span> <span data-keyword="substring-nonempty"><em>substring</em></span> in <code>s</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;babad&quot;
+<strong>Output:</strong> &quot;bab&quot;
+<strong>Explanation:</strong> &quot;aba&quot; is also a valid answer.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;cbbd&quot;
+<strong>Output:</strong> &quot;bb&quot;
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
+	<li><code>s</code> consist of only digits and English letters.</li>
+</ul>