public boolean isPalindrome(String s) {
if (s == null || s.length() == 0) {
int start = 0, end = s.length() - 1;
if (!Character.isLetterOrDigit(s.charAt(start))) {
else if (!Character.isLetterOrDigit(s.charAt(end))) {
else if (Character.toLowerCase(s.charAt(start)) != Character.toLowerCase(s.charAt(end))) {