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".

Note: KMP

class Solution {
public:
    string shortestPalindrome(string s) {
        string rev_s = s;
        reverse(rev_s.begin(), rev_s.end());
        string l = s + "#" + rev_s;

        vector<int> p(l.size(), 0);
        for (int i = 1; i < l.size(); i++) 
        {
            int j = p[i - 1];
            while (j > 0 && l[i] != l[j])
            {
                j = p[j - 1];
            }
            if (l[i] == l[j])
            {
                j++;
            }
            p[i] = j;
        }

        return rev_s.substr(0, s.size() - p[l.size() - 1]) + s;
    }
};