```
public boolean isPalindrome(String s) {
if (s == null || s.trim().equals("")) {
return true;
}
s = s.toLowerCase();
int left = 0;
int right = s.length() - 1;
while (left < right) {
while (! ((s.charAt(left) >= 'a' && s.charAt(left) <= 'z') || (s.charAt(left) >= '0' && s.charAt(left) <= '9'))) {
left++;
if (left == s.length()-1) return true;
}
while (! ((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;
}
```