public class DoublyLinkedList {
private Link first;
private Link last;
public DoublyLinkedList() {
first = null;
last = null;
}
public boolean isEmpty(){
return first == null;
}
public void insertFirst(long dd){
Link newLink = new Link(dd);
if (isEmpty())
last = newLink;
else
first.previous = newLink;
newLink.next = first;
first = newLink;
}
public void insertLast(long dd){
Link newLink = new Link(dd);
if (isEmpty())
first = newLink;
else {
last.next = newLink;
newLink.previous = last;
}
last = newLink;
}
public Link deleteFirst(){
Link temp = first;
if (first.next == null)
last = null;
else
first.next.previous = null;
first = first.next;
return temp;
}
public Link deleteLast(){
Link temp = last;
if (first.next == null)
first = null;
else
last.previous.next = null;
last = last.previous;
return temp;
}
public boolean insertAfter(long key, long dd) {
Link current = first;
while (current.dData != key){
current = current.next;
if (current == null)
return false; // cannot find it
}
Link newLink = new Link(dd); // make new link
if (current == last) // if last link,
{
newLink.next = null;
last = newLink;
} else // not last link,
{
newLink.next = current.next;
current.next.previous = newLink;
}
newLink.previous = current;
current.next = newLink;
return true; // found it, insert
}
public Link deleteKey(long key){
Link current = first;
while (current.dData != key)
{
current = current.next;
if (current == null)
return null; // cannot find it
}
if (current == first) // found it; first item?
first = current.next;
else
current.previous.next = current.next;
if (current == last) // last item?
last = current.previous;
else
// not last
current.next.previous = current.previous;
return current; // return value
}
public void displayForward() {
System.out.print("List (first to last): ");
Link current = first; // start at beginning
while (current != null) // until end of list,
{
current.displayLink();
current = current.next; // move to next link
}
System.out.println("");
}
public void displayBackward() {
System.out.print("List : ");
Link current = last;
while (current != null){
current.displayLink();
current = current.previous;
}
System.out.println("");
}
public static void main(String[] args) {
DoublyLinkedList theList = new DoublyLinkedList();
theList.insertFirst(22);
theList.insertFirst(44);
theList.insertLast(33);
theList.insertLast(55);
theList.displayForward();
theList.displayBackward();
theList.deleteFirst();
theList.deleteLast();
theList.deleteKey(11);
theList.displayForward();
theList.insertAfter(22, 77); // insert 77 after 22
theList.insertAfter(33, 88); // insert 88 after 33
theList.displayForward();
}
}
class Link {
public long dData; // data item
public Link next; // next link in list
public Link previous; // previous link in list
public Link(long d)
{
dData = d;
}
public void displayLink(){
System.out.print(dData + " ");
}
}
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