Shortest Palindrome
<p>You are given a string <code>s</code>. You can convert <code>s</code> to a <span data-keyword="palindrome-string">palindrome</span> by adding characters in front of it.</p>

<p>Return <em>the shortest palindrome you can find by performing this transformation</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> s = "aacecaaa"
<strong>Output:</strong> "aaacecaaa"
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> s = "abcd"
<strong>Output:</strong> "dcbabcd"
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= s.length &lt;= 5 * 10<sup>4</sup></code></li>
	<li><code>s</code> consists of lowercase English letters only.</li>
</ul>
String; String Matching; Hash Function; Rolling Hash
func shortestPalindrome(s string) string {
	n := len(s)
	base, mod := 131, int(1e9)+7
	prefix, suffix, mul := 0, 0, 1
	idx := 0
	for i, c := range s {
		t := int(c-'a') + 1
		prefix = (prefix*base + t) % mod
		suffix = (suffix + t*mul) % mod
		mul = (mul * base) % mod
		if prefix == suffix {
			idx = i + 1
		}
	}
	if idx == n {
		return s
	}
	x := []byte(s[idx:])
	for i, j := 0, len(x)-1; i < j; i, j = i+1, j-1 {
		x[i], x[j] = x[j], x[i]
	}
	return string(x) + s
}