input: 
  from typing import List
  
  def reverse_words(sentence: str) -> str:
      """Reverse the order of words in the given sentence while keeping the order of characters in each word unchanged.
      >>> reverse_words("This is a sentence.")
      "sentence. a is This"
      >>> reverse_words("Hello world")
      "world Hello"
      """
      words = sentence.split()
      return ' '.join(words[::-1])
  
output:     words = sentence.split()
      return ' '.join(words[::-1])