Add Two Numbers leetcode java

题目:

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

 

题解：

这道题就是给的加数是倒着给的，你返回的结果也是倒着写的，所以进位也反着进就好。

维护一个carry，加数大于9时候carry为1，也要注意两个数相加如果大于8的话，要写取模后的值。

 

代码如下：

 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/