<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();
        string s1=s;
        reverse(s1.begin(),s1.end());
        if(s1==s)
        return s;
        vector<vector<int>> dp(n,vector<int>(n,0));
        int maxi=1;
        string ans="";
        ans+=s[0];
        for(int i=0;i<n;i++)
        dp[i][i]=1;
        for(int i=1;i<n;i++)
        {
            if(s[i-1]==s[i])
            {
            dp[i-1][i]=1;
            maxi=2;
            ans=s.substr(i-1,2);
            }
        }
        for (int length = 3; length <= n; length++) { // Length from 3 to n
            for (int i = 0; i <= n - length; i++) { // Start index
                int j = i + length - 1; // End index
                if (s[i] == s[j] && dp[i + 1][j - 1]) {
                    dp[i][j] = 1;
                    if (length > maxi) {
                        maxi = length;
                        ans = s.substr(i, length);
                    }
                }
            }
        }
        // for(int i=0;i<n;i++)
        // {
        //     for(int j=0;j<n;j++)
        //     {
        //         cout<<dp[i][j]<<" ";
        //     }
        //     cout<<endl;
        // }
        return ans;
    }
};
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