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Deque.java
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Deque.java
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import java.util.Iterator;
import java.util.NoSuchElementException;
import edu.princeton.cs.algs4.StdOut;
public class Deque<Item> implements Iterable<Item> {
private int count;
private class Node {
Item value;
Node prev;
Node next;
Node(final Item value) {
this.value = value;
}
}
private Node front;
private Node rear;
// construct an empty deque
public Deque() {
count = 0;
front = null;
rear = null;
}
// is the deque empty?
public boolean isEmpty() {
return count == 0;
}
// return the number of items on the deque
public int size() {
return count;
}
// add the item to the front
public void addFirst(final Item item) {
if (item == null)
throw new IllegalArgumentException();
final Node newnode = new Node(item);
if (front == null) {
front = newnode;
rear = front;
} else {
newnode.next = front;
front.prev = newnode;
front = newnode;
}
count++;
}
// add the item to the back
public void addLast(final Item item) {
if (item == null)
throw new IllegalArgumentException();
final Node newnode = new Node(item);
if (rear == null) {
rear = newnode;
front = rear;
} else {
newnode.prev = rear;
rear.next = newnode;
rear = newnode;
}
count++;
}
// remove and return the item from the front
public Item removeFirst() {
if (count == 0)
throw new NoSuchElementException();
Item temp = front.value;
front = front.next;
if (front == null)
rear = null;
else
front.prev = null;
count--;
return temp;
}
// remove and return the item from the back
public Item removeLast() {
if (count == 0)
throw new NoSuchElementException();
Item temp = rear.value;
rear = rear.prev;
if (rear == null)
front = null;
else
rear.next = null;
count--;
return temp;
}
// return an iterator over items in order from front to back
public Iterator<Item> iterator() {
return new LinkedListIterator(front);
}
private class LinkedListIterator implements Iterator<Item> {
Node currNode;
public LinkedListIterator(final Node firsNode) {
currNode = firsNode;
}
@Override
public boolean hasNext() {
return currNode != null;
}
@Override
public Item next() {
if (currNode == null)
throw new NoSuchElementException();
final Item currValue = currNode.value;
currNode = currNode.next;
return currValue;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
// unit testing (required)
public static void main(final String[] args) {
Deque<Integer> dq = new Deque<>();
dq.addFirst(12);
dq.addLast(13);
dq.addFirst(11);
dq.addLast(14);
dq.addFirst(10);
dq.addLast(15);
dq.removeFirst();
dq.removeLast();
Iterator<Integer> it = dq.iterator();
while (it.hasNext())
StdOut.println(it.next());
}
}