<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 longestPalindrome(self, s: str) -> str:
        

        def checkpalindrome(low, high):

            while 0<=low<=high<len(s) and s[low] == s[high]:

                if self.maxLen < high - low + 1:
                    self.maxLen = high - low + 1
                    self.start = low
                low-=1
                high+=1
            
            return self.maxLen , self.start

        self.maxLen , self.start = 0, 0
        for i in range(len(s)):
            self.maxLen , self.start = checkpalindrome(i, i)
            self.maxLen , self.start = checkpalindrome(i, i+1)
        
        return s[self.start:self.start+self.maxLen]
16500