[125] LeetCode palindromic sequence verification

Title:
Given a string, verify that it is a palindrome string, consider only the alphabetic and numeric characters, can ignore letter case.

Description: In this problem, we define the empty string as a valid palindromic sequence.

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true
Example 2:

Input: "race a car"
Output: false

public class LeetCode125a {

    public boolean isPalindrome(String s) {
        if(s.length() == 0)
            return true;
        int l=0,r=s.length()-1;

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