input: Write a function to list the contents of a directory and return them as a list. If the directory is empty, return an empty list.
  assert list_directory_contents("path/to/directory")==["file1.txt", "file2.txt", "subdirectory"]
  assert list_directory_contents("path/to/empty_directory")==[]
  assert list_directory_contents("path/to/non_existent_directory")==[]
output: import os
  
  def list_directory_contents(directory):
      if not os.path.exists(directory):
          return []
      return os.listdir(directory)