input: Write a python function to check if a given string is a palindrome.
  assert is_palindrome("madam") == True
  assert is_palindrome("racecar") == True
  assert is_palindrome("hello") == False
  assert is_palindrome("A man a plan a canal Panama") == True
output: def is_palindrome(s):
      s = ''.join(e for e in s if e.isalnum()).lower()
      return s == s[::-1]