125. Valid Palindrome

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.

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public class Solution {
    public boolean isPalindrome(String s) {
        s = s.trim();
        if(s == null || s.length() == 0) return true;
        String oldStr = "";
        String newStr = "";
        int i = 0;
        int j = s.length() - 1;
        while(i < j){  //!Character.isLetterOrDigit(s.charAt(i));
            if(s.charAt(i) < '0' || s.charAt(i) > '9' && s.charAt(i) < 'A' || s.charAt(i) > 'Z' && s.charAt(i) < 'a' || s.charAt(i) > 'z'){
                System.out.println(i);
                    i++;
                    continue;
                }
              if(s.charAt(j) < '0' || s.charAt(j) > '9' && s.charAt(j) < 'A' || s.charAt(j) > 'Z' && s.charAt(j) < 'a' || s.charAt(j) > 'z'){
                    j--;
                    continue;
                }
              if(Character.toUpperCase(s.charAt(i)) != Character.toUpperCase(s.charAt(j))){
                 return false;
                }
             i++;
             j--;
            }
        
        return true;
    }
}