def sum(n1, n2): carry = 0 sum = Node(None) while n1 is not None or n2 is not None: cur_sum = carry if n1 is not None: cur_sum += n1.value n1 = n1.next if n2 is not None: cur_sum += n2.value n2 = n2.next carry = cur_sum / 10 sum.add_to_tail(cur_sum % 10) if carry > 0: sum.add_to_tail(carry) return sum.next
