Add Two Numbers II — medium DSA Problem

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not have leading zeros.

Example 1:

Input:
7 2 4 3
5 6 4
Output: 7 8 0 7

(7243 + 564 = 7807)

Example 2:

Input:
0
0
Output: 0

Constraints:

The number of nodes in each list is in the range [1, 100]
0 ≤ Node.val ≤ 9

Input format: Two lines of space-separated digits (most significant first).

Output format: Space-separated digits of the sum (most significant first).