Add Two Numbers Represented as Linked Lists

Given two linked lists representing two non-negative integers, where the digits are stored in reverse order (i.e., starting from the least significant digit to the most significant digit), each node contains a single digit. Your task is to add these two numbers and return the head of the linked list representing the sum of the numbers.

Example:

Input:

TestCase 1: 
List1: 2 -> 4 -> 3 -> -1
List2: 5 -> 6 -> 4 -> -1
 

Output:

7 -> 0 -> 8 -> -1

Explanation:

The numbers are 342 and 465. The sum is 807, and the linked list representation of the sum is 7 -> 0 -> 8 -> -1

Input:

The first line contains an integer T, the number of test cases.
Each test case consists of:
- Two lines containing elements of the first and second linked list respectively, terminated by -1.

Output:

For each test case, output the summed linked list, with elements space-separated and terminated by -1.

Constraints:

• 1 <= T <= 10
• 1 <= M, N <= 5 * 104
• 0 <= data[i] <= 9 and data[i] != -1

Where 'M' and 'N' are the number of nodes in the two linked lists, 'data[i]' is the data of the 'i-th' node.

Note: The numbers do not have leading zeros.