<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:
        dp = [[False for _ in range(len(s)+1)] for _ in range(len(s)+1)]
        answer = s[0]
        for i in range(len(s)):
            dp[i][i] = True
            if i < len(s)-1 and s[i] == s[i+1]:
                dp[i][i+1] =True
                answer = s[i:i+2]
        for diff in range(2, len(s)):
            for i in range(len(s)-diff):
                j = i + diff
                if s[i] == s[j] and dp[i+1][j-1]:
                    dp[i][j] = True
                    if j-i+1 > len(answer):
                        answer = s[i:j+1]
        return answer

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