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
func longestPalindrome(s string) string {
	n := len(s)
	f := make([][]bool, n)
	for i := range f {
		f[i] = make([]bool, n)
		for j := range f[i] {
			f[i][j] = true
		}
	}
	k, mx := 0, 1
	for i := n - 2; i >= 0; i-- {
		for 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[k : k+mx]
}