You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

翻译：

给定两个非空链表，代表两个非负整数。数字倒序存储，每个节点包含一个数字。求这两个数字的和并作为一个链表返回。你可以假设这两个数字除了0本身外不包含前导0。

Solution:

这个问题很简单，只要同时遍历两个链表并对两个 Node 的值求和，直到下一个 Node 都是null，一定要注意进位。

class Solution {
    fun addTwoNumbers(l1: ListNode?, l2: ListNode?): ListNode? {
        var node1 = l1
        var node2 = l2
        val result = ListNode(0)
        var current = result
        var c = 0
        while (true) {
            val sum = (node1?.`val` ?: 0) + (node2?.`val` ?: 0) + c
            current.`val` = sum % 10
            node1 = node1?.next
            node2 = node2?.next
            c = sum / 10
            if (node1 != null || node2 != null || c != 0) {
                current.next = ListNode(0)
                current = current.next!!
            } else {
                break
            }
        }
        return result
    }
}