Longest Palindromic Substring
<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>
Two Pointers; String; Dynamic Programming
/**
 * @param {string} s
 * @return {string}
 */
var longestPalindrome = function (s) {
    const n = s.length;
    const f = Array(n)
        .fill(0)
        .map(() => Array(n).fill(true));
    let k = 0;
    let mx = 1;
    for (let i = n - 2; i >= 0; --i) {
        for (let j = i + 1; j < n; ++j) {
            f[i][j] = false;
            if (s[i] === s[j]) {
                f[i][j] = f[i + 1][j - 1];
                if (f[i][j] && mx < j - i + 1) {
                    mx = j - i + 1;
                    k = i;
                }
            }
        }
    }
    return s.slice(k, k + mx);
};
