<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 {

private:
    bool check(int i, int j, string &s, vector <vector<int>> &dp){
        int n = s.size();

        if(i > j){
            return true;
        }

        if(dp[i][j] != -1) return dp[i][j];

        if(s[i] != s[j]){
            return dp[i][j] = false;
        }

        return dp[i][j] = check(i+1, j-1, s, dp);
    }

public:
    string longestPalindrome(string s) {
        int n = s.size();
        string ans;
        int maxi = 0;
        vector <vector<int>> dp(n, vector<int>(n, -1));

        for(int i=0; i<n; i++){
            string temp;
            for(int j=i; j<n; j++){
                temp.push_back(s[j]);
                if(check(i, j, s, dp)) {
                    if(j-i+1 > maxi){
                        maxi = j-i+1;
                        ans = temp;
                    }
                }
                
            }
        }

        return ans;
    }
};
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