LeetCode #2 Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored inreverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
 

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
      ListNode a=l1;
      ListNode b=l2;
      ListNode c=new ListNode(0);
      ListNode d=c;
       int sum=0; 
      while(a!=null||b!=null){
          sum/=10;
          if(a!=null){
              
          sum+=a.val;
          a=a.next;
          }
          if(b!=null){
          sum+=b.val;
          b=b.next;
          }
          d.next=new ListNode(sum%10);
          d=d.next;
    }
        if (sum / 10 == 1)
            d.next = new ListNode(1);
        return c.next;
}}