input: Write a function to reverse the order of words in a given string. If the string is empty, return an empty string. The function should handle strings with varying word lengths and whitespace.
  assert reverse_words("Hello world")== "world Hello"
  assert reverse_words("Python is great")== "great is Python"
  assert reverse_words("")== ""
  assert reverse_words("Single")== "Single"
  assert reverse_words("Extra  spaces here")== "here spaces Extra"
output: def reverse_words(s):
      words = s.split()
      reversed_words = words[::-1]
      return ' '.join(reversed_words)