<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) {
        if (isPalindrome(s)) return s;

        int n = s.length();
        string soln{};
        for (int i{}; i < n; ++i) {
            string tmp{};
            for (int j{i}; j < n; ++j) {
                tmp += s[j];
                if (tmp[0] == s[j] && isPalindrome(tmp)) {
                    if (tmp.length() > soln.length()) {
                        soln = tmp;
                    }
                }
            }
        }
        return soln;
    }
    bool isPalindrome(string s) {
        int n = s.length(), m = n / 2;
        for (int i{}; !(n & 1) ? i <= m : i < m ; ++i) {
            if (s[i] != s[n - i - 1]) return false;
        }
        return true;
    }
};
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