Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. 

The new list should be made by splicing together the nodes of the first two lists.

 1 class Solution {
 2 public:
 3     ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
 4         ListNode dummy(0), *cur = &dummy;
 5         while(l1 && l2) {
 6             if(l1->val <= l2->val) {
 7                 cur->next = l1;
 8                 cur = cur->next;
 9                 l1 = l1->next;
10             }
11             else {
12                 cur->next = l2;
13                 cur = cur->next;
14                 l2 = l2->next;
15             }
16         }
17         if(l1) cur->next = l1;
18         if(l2) cur->next = l2;
19         return dummy.next;
20     }
21 };