A Practical Introduction to Data Structures and Algorithm Analysis

110 Chap. 4 Lists, Stacks, and Queuesheadcurrtailhead20 23 12 15curr(a)tail20 23 10 12(b)15Figure 4.7 Insertion using a header node, with curr pointing one node head ofthe current element. (a) Linked list before insertion. The current node contains12. (b) Linked list after inserting the node containing 10.Figure 4.8 shows the definition for the linked list class, named LList. ClassLList inherits from the abstract list class and thus must implement all of ClassList’s member functions.Implementation for most member functions of the list class is straightforward.However, insert and remove should be studied carefully.Inserting a new element is a three-step process. First, the new list node iscreated and the new element is stored into it. Second, the next field of the newlist node is assigned to point to the current node (the one (after) the node that currpoints to). Third, the next field of node pointed to by curr is assigned to point tothe newly inserted node. The following line in the insert method of Figure 4.8actually does all three of these steps.curr.setNext(new Link(it, curr.next()));Operator new creates the new link node and calls the constructor for the Linkclass, which takes two parameters. The first is the element. The second is the valueto be placed in the list node’s next field, in this case “curr.next.” Figure 4.9illustrates this three-step process. Once the new node is added, tail is pushedforward if the new element was added to the end of the list. Insertion requires Θ(1)time.Removing a node from the linked list requires only that the appropriate pointerbe redirected around the node to be deleted. This memory will eventually bereclaimed by the garbage collector. The following lines from the remove methodof Figure 4.8 do precisely this.E it = curr.next().element(); // Remember valuecurr.setNext(curr.next().next()); // Remove from list