You have two numbers represented by a linked list, where each node contains a single digit. The digits are stored in forward order, such that the 1's digit is at the head of the list. Write a function that adds the two numbers and returns the sum as a linked list.

 class Solution {

 public:

     /**

      * @param l1: the first list

      * @param l2: the second list

      * @return: the sum list of l1 and l2

      */

     ListNode *addLists2(ListNode *l1, ListNode *l2) {

         reverse(l1);

         reverse(l2);

         ListNode *dummy = new ListNode();

         ListNode *tail = dummy;

         int carry = ;

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

             int sum = carry;

             if (l1 != NULL) {

                 sum += l1->val;

                 l1 = l1->next;

             }

             if (l2 != NULL) {

                 sum += l2->val;

                 l2 = l2->next;

             }

             if (sum > ) {

                 carry = ;

                 sum -= ;

             } else {

                 carry = ;

             }

             tail->next = new ListNode(sum);

             tail = tail->next;

         }

         if (carry == ) {

             tail->next = new ListNode();

             tail = tail->next;

         }

         reverse(dummy->next);

         return dummy->next;

     }

     void reverse(ListNode *&head) {

         ListNode *prev = NULL;

         while (head != NULL) {

             ListNode *temp = head->next;

             head->next = prev;

             prev = head;

             head = temp;

         }

         head = prev;

     }

 };

 public class Solution {

     /**

      * @param l1: the first list

      * @param l2: the second list

      * @return: the sum list of l1 and l2

      */

     public ListNode addLists2(ListNode l1, ListNode l2) {

         Stack<Integer> temp1 = reverseNode(l1);

         Stack<Integer> temp2 = reverseNode(l2);  

         ListNode point = new ListNode(0);

         int flag = 0;  

         while((!temp1.isEmpty()) && (!temp2.isEmpty())){

             int value = temp1.pop() + temp2.pop() + flag;

             flag = value / 10;

             value = value % 10;

             ListNode cur = new ListNode(value);

             cur.next = point.next;

             point.next = cur;

         }  

         while(!temp1.isEmpty()){

             int value = temp1.pop() + flag;

             flag = value / 10;

             value = value % 10;

             ListNode cur = new ListNode(value);

             cur.next = point.next;

             point.next = cur;

         }  

         while(!temp2.isEmpty()){

             int value = temp2.pop() + flag;

             flag = value / 10;

             value = value % 10;

             ListNode cur = new ListNode(value);

             cur.next = point.next;

             point.next = cur;

         }  

         if(flag == 1){

             ListNode cur = new ListNode(1);

             cur.next = point.next;

             point.next = cur;

         }  

         return point.next;

     }  

     public Stack<Integer> reverseNode(ListNode temp){

         Stack<Integer> record = new Stack<Integer>();  

         while(temp != null){

             record.push(temp.val);

             temp = temp.next;

         }  

         return record;

     }

 }