Given a string s, return true if s reads the same forward and backward after removing all non-alphanumeric characters and ignoring letter case. Implement an O (n)-time, O( 1)-extra-space solution using two pointers. Follow-ups: (a) Modify your solution to return true if s can become a palindrome after deleting at most one character; (b) Discuss how you would support full Unicode (e.g., combining marks and non-ASCII letters); (c) Provide test cases and analyze complexity.