<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:
    void solve(string s, int i, int j, string& str, int& len) {
        
        if (i < 0 || j >= s.length()) {
            return;
        }
        
       
        if (s[i] == s[j]) {
            if (len < j - i + 1) {
                str = s.substr(i, j - i + 1);
                len = j - i + 1;
            }
            
            solve(s, i - 1, j + 1, str, len);
        }
    }
    
    string longestPalindrome(string s) {
        int len = 0;
        string str;
        
        for (int i = 0; i < s.length(); ++i) {
            
            solve(s, i, i, str, len);
            
            solve(s, i, i + 1, str, len);
        }
        
        return str.empty() ? s.substr(0, 1) : str;
    }
};

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