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Dequeue.java
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Dequeue.java
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package a02;
import java.util.Deque;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.NoSuchElementException;
import edu.princeton.cs.algs4.*;
public class Dequeue<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 dequeue
public Dequeue()
{
}
// is the dequeue empty?
public boolean isEmpty()
{
return (size == 0);
}
// return the number of items on the dequeue
public int size()
{
return size;
}
// add the item to the front
public void addFirst(Item 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++;
}
// add the item to the back
public void addLast(Item 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++;
}
// remove and return the item from the front
public Item removeFirst()
{
Item item = first.item;
size--;
if (isEmpty()) {
first = null;
last = null;
} else {
first = first.next;
first.prev = null;
}
return item;
}
// remove and return the item from the back
public Item removeLast()
{
Item item = last.item;
size--;
if (isEmpty()) {
first = null;
last = null;
} else {
last = last.prev;
last.next = null;
}
return item;
}
// return an iterator over items in order from front to back
public Iterator<Item> iterator() {
return new dequeIterator();
}
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();
} else {
Item item = current.item;
current = current.next;
return item;
}
}
}
// unit testing (required)
public static void main(String[] args)
{
//Deque<String> deque = new Deque<String>(); //? why is deque throwing an error
Deque<String> deque = new LinkedList<String>();
StdOut.println("k = ");
int itrs = StdIn.readInt();
StdOut.print("input the strings: ");
for (int i = 0; i < itrs; i++)
{
while (!StdIn.isEmpty())
{
String s = StdIn.readString();
if (s.equals("-"))
StdOut.print(deque.removeLast());
else
deque.addFirst(s);
}
}
for (String d : deque)
{
StdOut.print(d);
}
}
}