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) {            char l = s.charAt(left), r = s.charAt(right);            if (!((l >= cl && l <= ch) || (l >= nl && l <= nh))) {                left++;                continue;            }            if (!((r >= cl && r <= ch) || (r >= nl && r <= nh))) {                right--;                continue;            }            if (l == r) {                left++;                right--;            } else {                return false;            }        }        return true;    }}