Leetcode 214: Shortest Palindrome

Given a string S, you are allowed to convert it to a palindrome by adding characters in front of it. Find and return the shortest palindrome you can find by performing this transformation.

For example:

Given "aacecaaa", return "aaacecaaa".

Given "abcd", return "dcbabcd".

 

public class Solution {
    public string ShortestPalindrome(string s) {
        int i = 0, end = s.Length - 1, j = end;
        
        while (i < j)
        {
            if (s[i] == s[j])
            {
                i++;
                j--;
            }
            else
            {
                i = 0;
                end--;
                j = end;
            }
        }
        
        var sb = new StringBuilder();
        
        for (int k = s.Length - 1; k > end; k--)
        {
            sb.Append(s[k]);
        }
        
        for (int k = 0; k < s.Length; k++)
        {
            sb.Append(s[k]);
        }
        
        return sb.ToString();
    }
}