Add Two Numbers (Linked List)

Problem Two non-negative numbers are given as linked lists of digits in reverse order (least-significant digit first). Add them and return the sum as a linked list in the same format.

Input / Output

• Input: heads of two linked lists, each a number stored least-significant-digit first.
• Output: the head of a linked list representing the sum.

Constraints

• Lists may differ in length; a final carry may add one extra digit.
• Each node holds a single digit 0–9.

Example

• [2,4,3] + [5,6,4] → [7,0,8] (342 + 465 = 807).