<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, st: str) -> str:
        # just do middle out
        n=len(st)
        def longest_with_center(s, l, r):
            if r > len(s)-1:
                return ''
            ans = ''
            if l==r:
                ans=s[l]
            if r==l+1:
                if s[r]==s[l]:
                    ans= s[l]+s[r]
                else:
                    return ''

            while l > 0 and r < len(s)-1:
                if s[l-1]==s[r+1]:
                    ans = s[l-1:r+2]
                else:
                    break
                l-=1
                r+=1
            return ans
        maxs=''
        maxlen=0
        for i in range(n):
            s1 = longest_with_center(st, i, i)
            s2 = longest_with_center(st, i, i+1)
            if len(s1) > maxlen:
                maxs=s1
                maxlen=len(maxs)
            if len(s2) > maxlen:
                maxs=s2
                maxlen=len(maxs)
                
        return maxs
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