<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>

class Solution:
    def shortestPalindrome(self, s: str) -> str:
        t = s + '#' + s[::-1]

        def build_z_func(text: str) -> List[int]:
            z_func = [0] * len(text)
            z_func[0] = len(text)

            l, r = 0, 0
            for i in range(1, len(text)):
                if i < r:
                    z_func[i] = min(z_func[i-l], r-i)
                
                while i+z_func[i] < len(text) and text[i+z_func[i]] == text[z_func[i]]:
                    z_func[i] += 1
                
                if i + z_func[i] > r:
                    l, r = i, i + z_func[i]
            
            return z_func
        

        z_func = build_z_func(t)
        for i in range(len(s) + 1, len(z_func)):
            if i + z_func[i] - 1 == len(z_func) - 1:
                return s[len(z_func) - i:][::-1] + s
        return ''
19400