"""
(Under Linked Lists)

Add Two Numbers II:

You are given two non-empty linked lists representing two non-negative integers.
The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.
"""
