You are given a string s. You can convert s to a palindrome by adding characters in front of it. Return the shortest palindrome you can find by performing this transformation. Example 1: Input: s = "aacecaaa" Output: "aaacecaaa" Example 2: Input: s = "abcd" Output: "dcbabcd" Constraints: 0 <= s.length <= 5 * 104 s consists of lowercase English letters only.