<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 strStr(self, a: str) -> int:
        m = len(a)
        lps = [0 for _ in range(m)]
        i = 0
        j = 1
        while j < m:
            if a[i] == a[j]:
                i += 1
                lps[j] = i
                j += 1
            elif i == 0:
                lps[j] = 0
                j += 1
            else:
                i = lps[i - 1]

        return lps[-1]

    def shortestPalindrome(self, s: str) -> str:
        if s == '': return ''
        t = self.strStr(s + '*' + s[::-1])
        return s[t:][::-1] + s
        

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