public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

         ListNode head = new ListNode(0);

         ListNode result = head;

         int carry = 0 , tempSum = 0;

         while(l1 != null || l2 != null){

             int v1 , v2;

             v1 = (l1 != null) ? l1.val : 0;

             v2 = (l2 != null) ? l2.val : 0;

             tempSum = v1 + v2 + carry;

             carry = tempSum / 10;

             tempSum = tempSum % 10;

             head.next = new ListNode(tempSum);

             head = head.next;

             l1 = (l1 != null) ? l1.next : null;

             l2 = (l2 != null) ? l2.next : null;

         }

         if(carry > 0) head.next = new ListNode(carry);

         return result.next;

     }