Add Two Numbers (Forward Order Linked Lists)

Problem: Add Two Numbers (Forward Order Linked Lists) You are given two singly linked lists l1 and l2. Each node contains a single digit (0-9). The digits are stored in forward order, meaning: The head node is the most significant digit. The tail node is the least significant digit. Compute the sum of the two numbers and return it as a linked list in the same forward order. Example l1 = 7 -> 2 -> 4 -> 3 represents 7243 l2 = 5 -> 6 -> 4 represents 564 Return: 7 -> 8 -> 0 -> 7 (represents 7807) Requirements You must define the ListNode structure yourself. You must write your own test cases (at least cover: different lengths, carry generation, and an extra carry at the most significant digit). Follow-up Solve it without reversing the input lists. Extra space is allowed. Constraints (typical interview assumptions) 1 <= len(l1), len(l2) <= 10^4 Node values are 0..9 Implement a function that: Input: heads l1, l2 Output: head of the summed list Example Input l1: 7 2 4 3 l2: 5 6 4 Output 7 8 0 7