input: Write a python function to check if a string is a palindrome.
  assert isPalindrome("racecar") == True
  assert isPalindrome("hello") == False
  assert isPalindrome("A man a plan a canal Panama") == True
  assert isPalindrome("Was it a car or a cat I saw") == True
  assert isPalindrome("No lemon no melon") == True
output: def isPalindrome(s):
      s = ''.join(c.lower() for c in s if c.isalnum())
      return s == s[::-1]