<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 {
public:
    string shortestPalindrome(string s) {
        if(s=="")return s;
        string t=s;
        reverse(t.begin(),t.end());
        s+=t;
        reverse(t.begin(),t.end());
        int n=s.size();
        vector<long long> z(n,0);
        z[0]=n;
        long long l=0,r=0;
        for(int i=1;i<n;i++){
            if(i<r)
            {
                z[i]=min(r-i,z[i-l]);
            }
            while(i+z[i]<n && (s[z[i]]==s[i+z[i]]))
            {
                 z[i]++;
            }
            if(i+z[i]>r)
            {
                l=i;
                r=i+z[i];
            }
                
            
        }
        int ind=-1;
        string p="";
        for(int i=n/2;i<n;i++){
            if(z[i]>=n-i){
                return p+t;
            }
            else{
                p+=s[i];
            }
        }
        return p+t;

    }
};
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