input: Write a python function to check if a string is a palindrome.
  assert isPalindrome("racecar") == True
  assert isPalindrome("hello") == False
  assert isPalindrome("madam") == True
  assert isPalindrome("step on no pets") == True
output: def isPalindrome(s: str) -> bool:
      cleaned = ''.join(c for c in s if c.isalnum()).lower()
      return cleaned == cleaned[::-1]