javal链表相加求和！

面试遇到一算法题：

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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
琢磨了一阵子，希望可以帮到有缘人。代码如下：

public class ListNode {
int val;
ListNode next;
ListNode(int x) { val = x; }
}

public class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
ListNode  listNode= new ListNode(0);
ListNode p = new ListNode(0);
p = listNode;
int sum = 0;

while (l1 != null || l2 != null || sum != 0) {
if (l1 != null) {
sum += l1.val;
l1 = l1.next;
}
if (l2 != null) {
sum += l2.val;
l2 = l2.next;
}
p.next = new ListNode(sum % 10);
sum = sum / 10;
p = p.next;
}
return listNode.next;
}
}