<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:
    int dp[1001][1001];
    bool isPalin(int i,int j,string &s){
        if(i>=j) return true;
        if(dp[i][j]!=-1) return dp[i][j];

        bool ans=true;
        while(i<j){
            if(s[i]!=s[j]){
                ans=false;
                break;
            }
            i++;
            j--; 
        }
        
        return dp[i][j]=ans;
    }
    string longestPalindrome(string s) {
        memset(dp,-1,sizeof(dp));
        int max_len=1,si=0,n=s.size();

        for(int i=0;i<n;i++){
            string temp="";
            for(int j=i;j<n;j++){
                temp+=s[j];
                if(isPalin(i,j,s)){
                    if(j-i+1>max_len){
                        max_len=j-i+1;
                        si=i;
                    }
                }
            }
        }

        return s.substr(si,max_len);
    }
};
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