def add(self, number):
        """
        Add the number to an internal data structure.
        :rtype: nothing
        """
        self.internal.append(number)
        if number in self.dic:
            # more than once
            self.dic[number] = True
            return
        # once
        self.dic[number] = False

        Add the number to an internal data structure.
        :rtype: nothing
        
python/170_Two_Sum_III-Data_structure_design.py