Merge Two Sorted Lists

Description:

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.

Code:

 1  ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
 2         if (!l1)
 3             return l2;
 4         else if (!l2)
 5             return l1;
 6         else
 7         {
 8             ListNode * head, *p, *q, *result;
 9             if (l1->val < l2->val)
10             {
11                 head = l1;
12                 p = l1->next;
13                 q = l2;
14             }
15             else
16             {
17                 head = l2;
18                 p = l1;
19                 q = l2->next;
20             }
21             result = head;
22             while (p&&q)
23             {
24                 if (p->val < q->val)
25                 {
26                     result->next = p;
27                     result = p;
28                     p = p->next;
29                 }
30                 else
31                 {
32                     result->next = q;
33                     result = q;
34                     q = q->next;
35                 }
36             }
37             result->next = (p==NULL)?q:p;
38              return head; 
39         }
40     }