leet code 002: Add Two Numbers? ? ? undone

Title description:

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

The main idea of ​​the topic:

Given two linked lists representing two non-negative integers respectively. The digits are stored in reverse order, and each node contains a single digit. Adds two numbers and returns them as a linked list.

Problem-solving ideas:

topic

Python code: