Valid Palindrome - LeetCode

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

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

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false

Java Solution :

class Solution {
    public boolean isPalindrome(String s) {
         if(s.length() == 0 || s == null)
             return true;
        int i =0;
        int j = s.length()-1;
        
        while(i < j){
            while(i < j && !Character.isLetterOrDigit(s.charAt(i))){
                i++;
            }
            while(i < j && !Character.isLetterOrDigit(s.charAt(j))){
                j--;
            }
            if(i<j && Character.toLowerCase(s.charAt(i++)) != Character.toLowerCase(s.charAt(j--)))
                return false;
        }
    return true;
    }
}