Determine if the input string is a palindrome (reads the same forwards and backwards), ignoring case and non-alphanumeric characters.
Examples:
Input: str = "A man, a plan, a canal: Panama"
Output: true
Explanation: After removing non-alphanumeric characters and converting to lowercase, "amanaplanacanalpanama" reads the same forwards and backwards.
Input: str = "race a car"
Output: false
Explanation: After cleaning, "raceacar" is not a palindrome.
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