Two non-negative whole numbers are stored in two linked lists. Each node holds one digit. The digits are stored in reverse order, so the first node is the ones digit. Find their sum and give it back in the same form, as a linked list.
A number never starts with zeros, unless the number is 0 itself.
How the judge passes the data
Examples
Example 1:
Input: l1 = [7,1,5], l2 = [2,9]
Output: [9,0,6]
Explanation: The numbers are 517 and 92. 517 + 92 = 609, and in reverse order that is [9,0,6].
Example 2:
Input: l1 = [0], l2 = [3]
Output: [3]
Explanation: 0 + 3 = 3.
Example 3:
Input: l1 = [9,9,9], l2 = [1]
Output: [0,0,0,1]
Explanation: 999 + 1 = 1000. In reverse order that is [0,0,0,1].