<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();
        vector<vector<bool>>dp(n+1,vector<bool>(n+1,false));
        for(int i=0;i<=n;i++){
            dp[n][i]=true;
            dp[i][i]=true;
        }
        for(int i=n-2;i>=0;i--){
            for(int j=i+1;j<=n-1;j++){
                if(s[i]!=s[j]){
                    dp[i][j]=false;
                }else{
                    if(j-1<=i+1){
                        dp[i][j]=true;
                    }else{
                        dp[i][j]=dp[i+1][j-1];
                    }
                }
            }
        }
        string s1="";
        for(int i=0;i<n;i++){
            string res="";
            for(int j=i;j<n;j++){
                    res+=s[j];
                    if(dp[i][j]==true){
                        if(s1.size()<res.size()){
                            s1=res;
                        }
                    }
            }
        }
        return s1;
        
    }
};
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