Add Two Numbers leetcode java

題目:

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) + (4 -> 6 -> 4)
Output: 6 -> 0 -> 8

 

題解：

這道題就是給的加數是倒著給的，你返回的結果也是倒著寫的，所以進位也反著進就好。

維護一個carry，加數大於9時候carry為1，也要注意兩個數相加如果大於8的話，要寫取模後的值。

 

程式碼如下：

 1     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
 2         if(l1==null)
 3             return l2;
 4         if(l2==null)
 5             return l1;
 6         
 7         int carry = 0;
 8         ListNode newhead = new ListNode(-1);
 9         ListNode l3 = newhead;
10         
11         while(l1!=null || l2!=null){
12             if(l1!=null){
13                 carry += l1.val;
14                 l1 = l1.next;
15             }
16             if(l2!=null){
17                 carry += l2.val;
18                 l2 = l2.next;
19             }
20             
21             l3.next = new ListNode(carry%10);
22             carry = carry/10;
23             l3 = l3.next;
24         }
25         
26         if(carry == 1)
27             l3.next=new ListNode(1);
28         return newhead.next;
29     }

 Reference: http://www.programcreek.com/2012/12/add-two-numbers/