Valid Palindrome -- Leetcode

Question:

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

Answer:
public boolean isPalindrome(String s) {
        for (int i = 0, j = s.length() - 1; i < j; i++, j--) {
            char a = s.charAt(i);
            char b = s.charAt(j);

            while (i < j && !Character.isLetter(a) && !Character.isDigit(a)) {
                a = s.charAt(++i);
            }

            while (j > i && !Character.isLetter(b) && !Character.isDigit(b)) {
                b = s.charAt(--j);
            }

            if (Character.toLowerCase(a) != Character.toLowerCase(b)) {
                return false;
            }
        }
        return true;
    }

Answer 2:

/*

public class EventBus {

HashMap<String, List<Event>>

public void register(String eventName, Event event) {};

public void unregister(String eventName, Event event){};

public void postEvent(String eventName, Object Data){};

public interface Event {

  void onEvent(Object data);

 }

}

*/

class EventBus {

  private Map<String, List<Event>> map;

  

  public EventListener() {

    map = new HashMap<String, List<Event>>();

  }

  

  public void register(String eventName, Event event) {

    if (map.containsKey(eventName)) {

      map.get(eventName).add(event);

    } else {

      List<Event> events = new ArrayList<Event>();

      events.add(event);

      map.put(eventName, events);

    }

  };

  

  public void unregister(String eventName, Event event) {

    if (map.containsKey(eventName)) {

      map.get(eventName).remove(event);

    }

  };

  public void postEvent(String eventName, Object data) {

if(map.containsKey(eventName)){

List<Event> events = map.get(eventName);

for(Event event : events){

event.doEvent(data);

}

}

 

/*Event event = new Event();

    event.doEvent(data);

    this.register(eventName, event);

    */

  };

} 

class Event {

  private Object data;

  public void doEvent(Object data) {

    this.data = data;

  };

}