Valid Palindrome

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