Add Two Integers Represented by Linked Lists

Statement

We are given the head pointers of two linked lists, each linked list represents an integer number (each node is a digit). Add them and return the resulting linked list (i.e., sum).

Here, the first node in a list represents the least significant digit.

Example

Sample input

[1, 0, 9, 9]
[7, 3, 2]

Expected output

[8, 3, 1, 0, 1]

Constraints

Only one positive digit (between $0$ and $9$ ...