input: Write a python function to convert a dictionary string back to a dictionary.
  assert convert_dict_string_to_dict('{"foo": "bar", "hello": "world"}') == {"foo": "bar", "hello": "world"}
  assert convert_dict_string_to_dict('{"name": "John", "age": 30}') == {"name": "John", "age": 30}
  assert convert_dict_string_to_dict('{}') == {}
output: def convert_dict_string_to_dict(dict_string):
      import ast
      return ast.literal_eval(dict_string)