Leetcode 125. Valid Palindrome

/** * Character methods. * isLetter(), isDigit(), isLetterOrDigit() * First check if characters are alphanumberic, * then check if characters are equal. */ public class Solution {    public boolean isPalindrome(String s) {        int low = 0, high = s.length()-1;        while (low < high) {            while (low < high && !Character.isLetterOrDigit(s.charAt(low))) low++;            while (low < high && !Character.isLetterOrDigit(s.charAt(high))) high--;            // the only possibility that two letters are palindrome when they are not equal is lower and upper letters            // therefore, when char is not letter its cannot be palindrome            if (s.charAt(low) != s.charAt(high)) {                if (!Character.isLetter(s.charAt(low)) || !Character.isLetter(s.charAt(high)) || Math.abs(s.charAt(low) - s.charAt(high)) != 32)                    return false;            }            low++;            high--;        }        return true;    }        public static boolean isAlphanumeric(char c) {        if (Character.isLetter(c) || Character.isDigit(c)) return true;        return false;    }}