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Deque.java
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Deque.java
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/**
* Deque creates an iterable double-ended queue.
* Items can be added and removed to both the front and the end.
*
* @author manyanair, insanorcross
* @version Summer 2022
*/
package a02;
import java.util.Iterator;
import java.util.NoSuchElementException;
import edu.princeton.cs.algs4.*;
public class Deque<Item> implements Iterable<Item>
{
private Node first = null;
private Node last = null;
private int size = 0;
private class Node
{
private Item item;
private Node next;
private Node prev;
}
// Construct an empty deque
public Deque()
{ }
/**
* Checks whether the Deque is empty.
*
* @return if the deque is empty or not.
*/
public boolean isEmpty()
{
return (size == 0);
}
/**
* Size of Deque.
*
* @return number of items in Deque
*/
public int size()
{
return size;
}
/**
* Adds an item to the front of the queue.
*
* @param item - to be added to Deque
*/
public void addFirst(Item item)
{
if (item == null)
throw new NullPointerException("Cannot add a null item");
Node oldFirst = first;
first = new Node();
first.item = item;
first.next = oldFirst;
first.prev = null;
if (isEmpty())
{
last = first;
}
else
{
oldFirst.prev = first;
}
size++;
}
/**
* Adds an item to the front of the queue.
*
* @param item - to be added to Deque
*/
public void addLast(Item item)
{
if (item == null)
throw new NullPointerException("Cannot add a null item");
Node oldLast = last;
last = new Node();
last.item = item;
last.next = null;
last.prev = oldLast;
if (isEmpty())
{
first = last;
}
else
{
oldLast.next = last;
}
size++;
}
/**
* Removes an item from the front of the queue.
*
* @return item - that was removed from Deque
*/
public Item removeFirst()
{
if (size == 0)
throw new NoSuchElementException("Cannot remove an item from an empty Deque");
Item item = first.item;
size--;
if (isEmpty())
{
first = null;
last = null;
}
else
{
first = first.next;
first.prev = null;
}
return item;
}
/**
* Removes an item from the end of the queue.
*
* @return item - that was removed from Deque
*/
public Item removeLast()
{
if (size == 0)
throw new NoSuchElementException("Cannot remove an item from an empty Deque");
Item item = last.item;
size--;
if (isEmpty())
{
first = null;
last = null;
}
else
{
last = last.prev;
last.next = null;
}
return item;
}
/**
* Creates iterator
*/
public Iterator<Item> iterator()
{
return new dequeIterator();
}
/**
* Implements the methods for the Iterable interface.
*/
private class dequeIterator implements Iterator<Item>
{
private Node current = first;
public boolean hasNext()
{
return current != null;
}
public void remove()
{
throw new UnsupportedOperationException();
}
public Item next()
{
if (!hasNext())
{
throw new NoSuchElementException("No more items");
}
else
{
Item item = current.item;
current = current.next;
return item;
}
}
}
// For testing purposes.
public static void main(String[] args)
{
Deque<String> deque = new Deque<String>();
// Check if empty deque was created
StdOut.println(deque.isEmpty());
// Test for edge case
//deque.removeFirst();
//deque.removeLast();
//deque.addFirst(null);
//deque.addLast(null);
// Add strings to deque
deque.addFirst("One");
deque.addLast("Two");
deque.addFirst("Three");
deque.addLast("Four");
// Print resulting deque
StdOut.println(deque.size());
for (String d : deque)
{
StdOut.print(d + ' ');
}
// Remove items from deque
deque.removeFirst();
deque.removeLast();
// Print resulting deque
StdOut.println("\n" + deque.size());
for (String d : deque)
{
StdOut.print(d + ' ');
}
}
}