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:

 ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if (!l1)
            return l2;
        else if (!l2)
            return l1;
        else
        {
            ListNode * head, *p, *q, *result;
            if (l1->val < l2->val)
            {
                head = l1;
                p = l1->next;
                q = l2;
            }
            else
            {
                head = l2;
                p = l1;
                q = l2->next;
            }
            result = head;
            while (p&&q)
            {
                if (p->val < q->val)
                {
                    result->next = p;
                    result = p;
                    p = p->next;
                }
                else
                {
                    result->next = q;
                    result = q;
                    q = q->next;
                }
            }
            result->next = (p==NULL)?q:p;
             return head; 
        }
    }