<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>

class Solution:
    def extend_palindrome(self, s: str, left: int, right: int) -> str:
        while left >= 0 and right < len(s) and s[left] == s[right]:
            left -= 1
            right += 1

        return s[left+1: right]


    def longestPalindrome(self, s: str) -> str:
        if len(s) == 1:
            return s

        if len(s) == 2:
            if s[0] == s[1]:
                return s
            else:
                return s[0]

        max_length = 0
        longest_palindrome = ""

        for i in range(len(s)):
            
            # odd-length palindrom
            palindrome = self.extend_palindrome(s, i, i+1)

            if len(palindrome) > max_length:
                max_length = len(palindrome)
                longest_palindrome = palindrome


            # even-length palindrom
            palindrome = self.extend_palindrome(s, i, i)
            if len(palindrome) > max_length:
                max_length = len(palindrome)
                longest_palindrome = palindrome

        return longest_palindrome
        
        
16400