125. 验证回文串

输入: "A man, a plan, a canal: Panama"
输出: true

输入: "race a car"
输出: false

class Solution {
    public boolean isPalindrome(String s) {
        if (s == null) {
            return false;
        }
        if ("".equals(s)) {
            return true;
        }
        if (".,".equals(s)) {
            return true;
        }
        int i = 0;
        int j = s.length() - 1;
        while (i < j) {
            while (i < s.length() - 1 && !Character.isLetterOrDigit(s.charAt(i))) {
                i++;
            }
            while (j > 0 && !Character.isLetterOrDigit(s.charAt(j))) {
                j--;
            }
            if (Character.toLowerCase(s.charAt(i)) == Character.toLowerCase(s.charAt(j))) {
                i++;
                j--;
            } else {
                return false;
            }
        }
        return true;
    }
}