def complement(self, alphabet):
        """
        Returns the complement of DFA
        Args:
            alphabet (list): The input alphabet
        Returns:
            None
        """
        states = sorted(self.states, key=attrgetter('initial'), reverse=True)
        for state in states:
            if state.final:
                state.final = False
            else:
                state.final = True
Returns the complement of DFA
        Args:
            alphabet (list): The input alphabet
        Returns:
            None