input: Write a function to sort a list of strings based on their length. If the list is empty, return the empty list.
  def sort_strings_by_length(words):
      if not words:
          return words
      words.sort(key=len)
      return words
  assert sort_strings_by_length(["Hello","World!","Good","Morning"])==['Good', 'Hello', 'World!', 'Morning']
  assert sort_strings_by_length([])==[]
  assert sort_strings_by_length(["a","bb","ccc","dd"])==['a', 'bb', 'dd', 'ccc']
output: def sort_strings_by_length(words):
      if not words:
          return words
      words.sort(key=len)
      return words