<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) {
        string str=s;
        reverse(str.begin(),str.end());
        string s1 = s+"#"+str;

           int i=0,j=1;
    vector<int> v;
    v.push_back(0);
    while(j<s1.length()){
        if(s1[i]==s1[j]){
            i++;
            j++;
            v.push_back(i);
        }
        else{
            if(i==0){
              j++;
              v.push_back(i);
            }
            else{
                i=v[i-1];
            }
            
        }
    }

 
     int n=s.length(), n1 = v[s1.length()-1];
     string s2 = s.substr(n1,n-n1);
     reverse(s2.begin(),s2.end());
     return s2+s;
    }
};
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