<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) {
        int n = s.length();
        if (n == 0 || n == 1) {
            return s;
        }
        
        int start = 0;
        for (int end = n - 1; end >= 0; --end) {
            if (s[end] == s[start]) {
                start++;
            }
        }
        
        if (start == n) { 
            return s;
        }
        
        string suffix = s.substr(start);
        reverse(suffix.begin(), suffix.end());
        
        return suffix + shortestPalindrome(s.substr(0, start)) + s.substr(start);
    }
};

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