<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 {
public:

    string math(int l, int r, string maxstr, string s){
        while(l >= 0 && r < s.size() && s[l] == s[r]){
            if((r - l + 1) > maxstr.size()){
                maxstr = s.substr(l, (r - l + 1));
            }
            l--;
            r++;
        }
        return maxstr;
    }

    string longestPalindrome(string s) {
        string maxstr = "";

        for(int i = 0;i < s.size();i++){
            //odd
            maxstr = math(i, i, maxstr, s);
            //even
            maxstr = math(i, i+1, maxstr, s);
        }
        return maxstr;
    }
};
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