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;
}
}