leetcode_add two number

原题:
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.

Java
这是已给定的JAVA版数据结构
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
题目大意：
根据给定的数据结构完成要求，输入是两个list，对list的每个节点相加，有进位，null为0，返回结果是一个ListNode

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    }
}

我的解决：

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode root = new ListNode(0);
        ListNode tmp = root;
        root.val = l1.val;
        int add = 0;
        while (l1!=null||l2!=null) {
            int a = (l1 == null) ? 0 :l1.val;
            int b = (l2 == null) ? 0 :l2.val;
            int sum = a+b+add;
            add=sum/10;
            tmp.next = new ListNode(sum%10);
            tmp = tmp.next;
            if (l1!=null) 
                l1 = l1.next;
            if (l2!=null)
                l2 = l2.next;
        }
        if (add>0) {
            tmp.next = new ListNode(add);
        }
        return root.next;
    }
}