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
impl Solution {
    pub fn longest_palindrome(s: String) -> String {
        let (n, mut ans) = (s.len(), &s[..1]);
        let mut dp = vec![vec![false; n]; n];
        let data: Vec<char> = s.chars().collect();

        for end in 1..n {
            for start in 0..=end {
                if data[start] == data[end] {
                    dp[start][end] = end - start < 2 || dp[start + 1][end - 1];
                    if dp[start][end] && end - start + 1 > ans.len() {
                        ans = &s[start..=end];
                    }
                }
            }
        }
        ans.to_string()
    }
}
