Add Two Numbers

You are given two linked lists representing two non-negative numbers. 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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) {
 7  *         val = x;
 8  *         next = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
14         if(null == l1)
15             return l2;
16         if(null == l2)
17             return l1;
18         ListNode head = new ListNode(0);
19         ListNode ptr = head;
20         int carry = 0;                                            //进位
21         while(null != l1 && null != l2){
22             ListNode temp = new ListNode(l1.val + l2.val);
23             temp.next = null;
24             ptr.next = temp;
25             ptr = ptr.next;
26             l1 = l1.next;
27             l2 = l2.next;
28         }
29         while(null != l1){
30             ListNode temp = new ListNode(l1.val);
31             ptr.next = temp;
32             temp.next = null;
33             ptr = ptr.next;
34             l1 = l1.next;
35         }
36         while(null != l2){
37             ListNode temp = new ListNode(l2.val);
38             ptr.next = temp;
39             temp.next = null;
40             ptr = ptr.next;
41             l2 = l2.next;
42         }
43         //开始进位    
44         ptr = head.next;
45         while(null != ptr){
46             ptr.val = ptr.val + carry;
47             carry = ptr.val / 10;
48             ptr.val %= 10;
49             ptr = ptr.next;
50         }
51         if(1 == carry){
52             ptr = head.next;
53             while(null != ptr.next)
54                 ptr = ptr.next;
55             ListNode temp = new ListNode(1);
56             temp.next = null;
57             ptr.next = temp;
58         }
59         
60         return head.next;
61     }
62 }