<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 longestPalindrome(string s) {
        int best_len = 0;
        string best_s = "";
        int n = s.length();
        for(int mid = 0; mid < n; mid++){
            for(int x = 0; mid - x >= 0 && mid + x < n; x++){
                if(s[mid-x] != s[mid+x]){
                    break;
                }
                int len = 2 * x + 1;
                if(len > best_len){
                    best_len = len;
                    best_s = s.substr(mid - x, len);
                }
            }
        }

        for(int mid = 0; mid < n - 1; mid++){
            for(int x = 1; mid - x + 1 >= 0 && mid + x < n; x++){
                if(s[mid-x + 1] != s[mid+x]){
                    break;
                }
                int len = 2 * x;
                if(len > best_len){
                    best_len = len;
                    best_s = s.substr(mid - x + 1, len);
                }
            }
        }
        return best_s;
    }
};
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