Data Structures and Algorithm Analysis - Computer Science at ...

114 Chap. 4 Lists, Stacks, and Queues/** Doubly linked list node */class DLink {private E element;// Value for this nodeprivate DLink next; // Pointer to next node in listprivate DLink prev; // Pointer to previous node}/** Constructors */DLink(E it, DLink p, DLink n){ element = it; prev = p; next = n; }DLink(DLink p, DLink n) { prev = p; next = n; }/** Get and set methods for the data members */DLink next() { return next; }DLink setNext(DLink nextval){ return next = nextval; }DLink prev() { return prev; }DLink setPrev(DLink prevval){ return prev = prevval; }E element() { return element; }E setElement(E it) { return element = it; }Figure 4.14 Doubly linked list node implementation with a freelist.of the header and tailer nodes mean that there are no special cases to worry aboutwhen inserting into an empty list.The append method is also simple. Again, the Link class constructor sets theelement, prev, and next fields of the node when the new operator is executed.Method remove (illustrated by Figure 4.17) is straightforward, though thecode is somewhat longer. First, the variable it is assigned the value being removed.Note that we must separate the element, which is returned to the caller,from the link object. The following lines then adjust the list.E it = curr.next().element(); // Remember valuecurr.next().next().setPrev(curr);curr.setNext(curr.next().next()); // Remove from listThe first line stores the value of the node being removed. The second line makesthe next node’s prev pointer point to the left of the node being removed. Finally,the next field of the node preceding the one being deleted is adjusted. The finalsteps of method remove are to update the list length and return the value of thedeleted element.The only disadvantage of the doubly linked list as compared to the singly linkedlist is the additional space used. The doubly linked list requires two pointers pernode, and so in the implementation presented it requires twice as much overheadas the singly linked list.