給定兩個非空鏈表來表示兩個非負整數。位數按照逆序方式存儲，它們的每個節點只存儲單個數字。將兩數相加返回一個新的鏈表。你可以假設除了數字 0 之外，這兩個數字都不會以零開頭。

示例：

輸入：(2 -> 4 -> 3) + (5 -> 6 -> 4)

輸出：7 -> 0 -> 8

原因：342 + 465 = 807

代碼一：

 1     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
 2         ListNode result = new ListNode(0);
 3         ListNode first = l1, second = l2, tmpNode = result;
 
 4         int tmp = 0;
 5         
 6         while(first != null || second != null){
 7             int firstValue ,secondValue;
 8             if(first == null){firstValue = 0;}
 9             else{firstValue = first.val;}
10             
11             if(second == null){secondValue = 0;}
12             else
 
{secondValue = second.val;}
13             
14             tmp = tmp + firstValue + secondValue;
15             tmpNode.next = new ListNode(tmp % 10);
16             tmp = tmp / 10;
17             
18             tmpNode = tmpNode.next;
19             if(first != null){first = first.next;}
20             if
 
(second != null){second = second.next;}
21         }
22         if(tmp != 0){
23             tmpNode.next = new ListNode(tmp % 10);
24         }
25         return result.next;
26     }

代碼二：

 1 public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
 2     ListNode dummyHead = new ListNode(0);
 3     ListNode p = l1, q = l2, curr = dummyHead;
 4     int carry = 0;
 5     while (p != null || q != null) {
 6         int x = (p != null) ? p.val : 0;
 7         int y = (q != null) ? q.val : 0;
 8         int sum = carry + x + y;
 9         carry = sum / 10;
10         curr.next = new ListNode(sum % 10);
11         curr = curr.next;
12         if (p != null) p = p.next;
13         if (q != null) q = q.next;
14     }
15     if (carry > 0) {
16         curr.next = new ListNode(carry);
17     }
18     return dummyHead.next;
19 }

鏈表表示的兩數相加