private boolean isAlphaNum(char ch) {
        if ((ch >= '0' && ch <= '9') || (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')) {
            return true;
        }
        return false;
    }
Date 04/09/2016
@author Tushar Roy

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

https://leetcode.com/problems/valid-palindrome/
src/com/interview/string/ValidPalindrome.java