input: Write a function to reverse the order of words in a given sentence while maintaining the order of characters in each word. Return the resultant string after reversing the order of words. If the input string is empty, return an empty string.
  
  def reverse_words(string):
    if not string:
      return ""
    words = string.split(" ")
    reversed_words = []
    for word in words:
      reversed_words.insert(0, word)
    return ' '.join(reversed_words)
  
  assert reverse_words("This is a sentence.") == "sentence. a is This"
  assert reverse_words("Hello World") == "World Hello"
  assert reverse_words("Python") == "Python"
  assert reverse_words("") == ""
  assert reverse_words("One two Three") == "Three two One"
output: def reverse_words(string):
    if not string:
      return ""
    words = string.split(" ")
    reversed_words = []
    for word in words:
      reversed_words.insert(0, word)
    return ' '.join(reversed_words)