Min Chars to Add for Palindrome

class Solution {
    public static int minChar(String s) {
        String rev = new StringBuilder(s).reverse().toString();
        String concat = s + "$" + rev;
        int[] lps = new int[concat.length()];
        int j = 0;
        for (int i = 1; i < concat.length(); i++) {
            while (j > 0 && concat.charAt(i) != concat.charAt(j)) {
                j = lps[j - 1];
            }
            if (concat.charAt(i) == concat.charAt(j)) {
                j++;
            }
            lps[i] = j;
        }
        return s.length() - lps[concat.length() - 1];
    }
}