LeetCode#2 Add Two Numbers

public class Solution {
   public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
       ListNode ret = new ListNode(0);
       ListNode cur = ret;

       int sum = 0;
       while(true) {
           if(l1 != null) {
               sum += l1.val;
               l1 = l1.next;
           }
           if(l2 != null) {
               sum += l2.val;
               l2 = l2.next;
           }
           cur.val = sum % 10;
           sum /= 10;

           if(l1 != null || l2 != null || sum != 0) {
               //cur = (cur.next = new ListNode(0));
               cur.next = new ListNode(0);
               cur = cur.next;
           } else {
               break;
           }
       }
       return ret;
   }
}