Sum Of Two Numbers

Given 2 non-empty linked lists that represent non-negative integers, add the two numbers and return it as a linked list in reverse order.

Note: The 2 given linked lists are in reverse order and each linked list node can only store one digit.

Example:

Input: (1 -> 2 -> 3) + (4 -> 5 -> 6)
Output: 5 -> 7 -> 9
Explanation: 321 + 654 = 975.

Linked List
Math
Python 3