2. Add Two Numbers

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

 public ListNode AddTwoNumbers(ListNode l1, ListNode l2) {
        /*if (l1 == null) return l2;
        if (l2 == null) return l1;
        ListNode newNode = new ListNode(0);
        ListNode nextNode = new ListNode(0);
        newNode.val = (l1.val + l2.val)%10;
        newNode.next = nextNode;
        nextNode =  AddTwoNumbers( l1.next,  l2.next);
        nextNode.val +=((l1.val + l2.val)/10 ==1)? 1 : 0;*/
        //return AddTwoNumbers(l1,l2,0);
        ListNode result = new ListNode(0);
    int add = 0;
    if(l1 == null) return l2;
    if(l2 == null) return l1;
    int sum =0;
    ListNode stand = result;
    while((l1 != null)||(l2 != null))
     {
          if(l1 != null)
        {
            sum += l1.val; 
            l1 = l1.next;
        }
        if(l2 != null)
        {
            sum += l2.val; 
            l2 = l2.next;
        }
        //sum+=add;
        
        result.next =  new ListNode(sum%10);
        result = result.next;
        sum = sum/10;

     }    
    //judge highest digit add or not
    result.next = (sum==1)?new ListNode(1):null;

    return stand.next; 
}