<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) {
        list<char> maxChars;
        for (int i = 0; i < s.size(); i++) {
            
            list<char> chars;
            int left = i;
            int right = i;
            chars.push_back(s[i]);
            
            while (left-1 >= 0 && right+1 < s.size()) {
                if (s[left-1] == s[right+1]) {
                    chars.push_front(s[--left]);
                    chars.push_back(s[++right]);
                } else {
                    break;
                }
            }
            if (chars.size() > maxChars.size()) {
                maxChars = chars;
            }

            if (i+1 < s.size() && s[i] == s[i+1]) {
                chars.clear();
                int left = i;
                int right = i;
                chars.push_back(s[i]);
                chars.push_back(s[++right]);
                
                while (left-1 >= 0 && right+1 < s.size()) {
                    if (s[left-1] == s[right+1]) {
                        chars.push_front(s[--left]);
                        chars.push_back(s[++right]);
                    } else {
                        break;
                    }
                }
                if (chars.size() > maxChars.size()) {
                    maxChars = chars;
                }
            }
            
        }
        return std::string(maxChars.begin(), maxChars.end());
    }
};
397983