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.

Note:

Two pointers

Code:

public class Solution {
    public boolean isPalindrome(String s) {
        if (s == null) {
            return false;
        }
        if (s.length() < 2) {
            return true;
        }
        s = s.toLowerCase();
        int left = 0;
        int right = s.length() - 1;
        while (left < right) {
            while (left < right && !(s.charAt(left) >= 'a' && s.charAt(left) <= 'z') && 
            !(s.charAt(left) >= '0' && s.charAt(left) <= '9')) {
                left++;
            }
            while (left < right && !(s.charAt(right) >= 'a' && s.charAt(right) <= 'z') && 
            !(s.charAt(right) >= '0' && s.charAt(right) <= '9')) {
                right--;
            }            
            if (s.charAt(left) != s.charAt(right)) {
                return false;
            }
            left++;
            right--;
        }
        return true;
    }
}