<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.empty()) return s;
        string s1 = s;
        s1+='&';
        string s2 = s;
        reverse(s2.begin(), s2.end());
        s1+=s2;
        int pre =0, suf = 1, n = s1.size();
        vector<int> lcs(n, 0);
        while(suf<n){
            if(s1[pre] == s1[suf]) {
                lcs[suf] = pre+1;
                pre++, suf++;
            }else{
                if(pre == 0) suf++;
                else pre = lcs[pre - 1];
            }
        }
        int x = lcs[n-1];

        string ans= s.substr(x);
        cout<<ans;
        reverse(ans.begin(),ans.end());

        return ans + s;
        
    }

};
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