For our last problem, we’re going to pretend that each node in a linked list holds the digit of a number. The tail node holds the most significant digit and the head node holds the least significant digit.

# 2 -> 4 -> 1
# represents the number 142
# 7 -> 1
# represents the number 17

Given two of these linked lists, write a function that returns the sum of the two numbers as a new linked list.

# 2 -> 4 -> 1
# plus
# 7 -> 1
# returns
# 9 -> 5 -> 1

To recap:

• write a function: add_two().
• add_two() takes two arguments, each an instance of LinkedList.
• return an instance of LinkedList which contains the sum of the input linked lists.