<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 ans;
    bool isPalin(int l, int r, string &s){
        int x = l, y = r;
        while(l <= r) if(s[l++] != s[r--]) return false;
        if(ans.length() <= y - x + 1){
            ans = s.substr(x, y - x + 1);
        }
        return true;
    }
    void fun(int l, int r, string &s, vector<vector<int>> &dp){
        if(l >= s.length() || l > r || r < 0) return;
        if(dp[l][r] != -1) return;
        if(s[l] == s[r]){
            if(isPalin(l,r,s)){
                dp[l][r] = 1;
                return;
            }
            // else 
        } 
            dp[l][r] = 0;
            fun(l+1,r,s,dp);
            fun(l,r-1,s,dp);
        
        
    }
    string longestPalindrome(string s) {
        int n = s.length();
        vector<vector<int>> dp(n,vector<int>(n,-1));
        fun(0,n-1,s,dp);
        return ans;
    }
};
295196