<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 expand(int st, int dr, string s){
        string temp;
        while (st >= 1 && dr < s.length() - 1 && s[st - 1] == s[dr + 1]) {
            st--;
            dr++;
        }
        temp = s.substr(st, dr-st+1);
        return temp;
    }
    string longestPalindrome(string s) {
        string s1, s2;
        string maxim = string(1, s[0]);
        for(int i = 0; i < s.length()-1; i ++){
            s1 = expand(i , i , s);
            if(s[i] == s[i+1]) s2 = expand(i, i+1, s);
            if(s1.length() > maxim.length()) maxim = s1;
            if(s2.length() > maxim.length()) maxim = s2;
        }
        return maxim;
    }
    
};
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