Compute the sum of two non-empty linked lists, each representing a non-negative integer. he individual digits of these integers are stored in the linked lists in reverse order, with each node holding a single digit. The result of the addition should be returned as a linked list.
| Challenge | Solution |
private data class ListNode(
var data: Int,
var next: ListNode? = null,
)
val i1 = ListNode(1)
i1.next = ListNode(3)
val i2 = ListNode(11)
addTwoNumbers(i1, i2) // returns ListNode(2, ListNode(4))