<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 n = s.size();
        map <int, set <int>> solutions;
        for(int i = 0; i < n; i++){
            solutions[1].insert(i);
        }
        int maxlen = 1;
        int lastindex = 0;
        for(int i = 0; i < n-1; i++){
            if (s[i] == s[i+1]){
                lastindex = i;
                solutions[2].insert(i);
                maxlen = 2;
            }
        }
        for(int size = 3; size <= n; size++){
            for(int i = 0; i < n-size+1; i++){
                if ((s[i] == s[i + size - 1]) && (solutions[size-2].find(i+1) != solutions[size-2].end())){
                    solutions[size].insert(i);
                    lastindex = i;
                    maxlen = size;
                }
            }
        }
        string t;
        for(int i = 0; i < maxlen; i++){
            t += s[lastindex++];
        }
        return t;

    }
};
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