Valid Palindrome

public class Solution {
    /**
     * @param s A string
     * @return Whether the string is a valid palindrome
     */
    public static boolean isPalindrome(String s) {
        if (s == null || s.isEmpty()){
            return true;
        }
        int left = 0;
        int right = s.length() - 1;
        while (left < right){
            if (!Character.isLetterOrDigit(s.charAt(left))){
                ++left;
                continue;
            }
            if (!Character.isLetterOrDigit(s.charAt(right))){
                --right;
                continue;
            }
            if (Character.toLowerCase(s.charAt(left)) == Character.toLowerCase(s.charAt(right))){
                ++left;
                --right;
            } else {
                return false;
            }
        }
        return true;
    }
}