input: Write a python function to reverse the order of words in a given string.
  assert reverse_words("hello world") == "world hello"
  assert reverse_words("Python is fun") == "fun is Python"
  assert reverse_words("OpenAI is amazing") == "amazing is OpenAI"
output: def reverse_words(s: str) -> str:
      return ' '.join(s.split()[::-1])