Palindrome String - Coding Interview Problem

Given a string, you need to determine whether it is a palindrome or not.

A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward. For example, "racecar" is a palindrome because if you reverse the order of its letters, you still get "racecar". Similarly, "level", "deified", and "A man a plan a canal Panama" are all palindromes.

Write a function that takes a string as input and returns true if the string is a palindrome, or false otherwise.

For the purposes of this problem, you should ignore any non-alphanumeric characters and treat upper-case and lower-case letters as the same character.