leetcode125. palindromic sequence verification (the double pointer traversal)

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

class Solution {
    public boolean isPalindrome(String s) {
    
        if(s==null||s.length()==0){
            return true;
        }
        String str = s.replaceAll("[^0-9a-zA-Z]", "").toLowerCase();;  
        int length=str.length();
        for(int i=0,j=length-1;i<j;i++,j--){
        if( str.charAt(i)!= str.charAt(j)) 
            return false;   
        } 
return true;
    }
}