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.

代码：

    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(l1 == NULL)
            return l2;
        if(l2 == NULL)
            return l1;
        ListNode *result, *head = NULL;
        if(l1->val < l2->val){
            head = l1;
            l1 = l1->next;
        }            
        else{
            head = l2;
            l2 = l2->next;
        }
        result = head;
        while(l1 && l2){
            if(l1->val < l2->val){
                result->next = l1;
                l1 = l1->next;
            }
            else{
                result->next = l2; 
                l2 = l2->next;
            }
            result = result->next;
        }
        if(l1 == NULL)
            result->next = l2;
        else
            result->next = l1;
        return head;
    }