Two Pointers Problems

Valid Palindrome

public static boolean isPalindrome(String s) {
        int l = 0, r = s.length() - 1;
        s = s.toLowerCase();

        if (s.isEmpty()) return true;
        while (l <= r) {
            while (l < r && !Character.isLetterOrDigit(s.charAt(l))) l++;
            while (l < r && !Character.isLetterOrDigit(s.charAt(r))) r--;
            if (s.charAt(l) != s.charAt(r)) return false;
            l++;
            r--;
        }
        return true;
    }