Add Two Numbers

Problem:

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

Analysis:
Need to create a new ListNode other than the returned one. Because each iteration would cause the new ListNode point to its next node, keep the head is necessary.

Solution:

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:      int carry=0;  
15:      ListNode result=new ListNode(0);  
16:      ListNode l3=result;  
17:      while(l1!=null || l2!=null)  
18:      {  
19:        if(l1!=null)  
20:        {  
21:          carry+=l1.val;  
22:          l1=l1.next;  
23:        }  
24:        if(l2!=null)  
25:        {  
26:          carry+=l2.val;  
27:          l2=l2.next;  
28:        }  
29:        l3.next=new ListNode(carry%10);  
30:        carry/=10;  
31:        l3=l3.next;  
32:      }  
33:      if(carry==1)  
34:      {  
35:       l3.next=new ListNode(1);    
36:      }  
37:      return result.next;  
38:    }  
39:  }