merge.cpp

ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode *newList = NULL, *newTail = NULL;
        
        while(l1 != NULL && l2 != NULL)
        {
            ListNode *newNext = (l1->val < l2->val) ? l1 : l2;
            if(newList == NULL)
            {
                newList = newNext;
                newTail = newNext;
            }
            else
            {
                newTail->next = newNext;
                newTail = newNext;
            }
            if(newNext == l1)
                l1 = l1->next;
            else
                l2 = l2->next;
        }

        if(l1 != NULL)
        {
            if(newList == NULL)
                newList = l1;
            else
                newTail->next = l1;
        }
        if(l2 != NULL)
        {
            if(newList == NULL)
                newList = l2;
            else
                newTail->next = l2;
        }
        return newList;
    }