solve this java file (ALL the to do parts):

You will use Queue.java from course source.

package hw5;

import java.util.Iterator;
import java.util.NoSuchElementException;

public class PriceQueue implements Iterable {
private Node first; // beginning of queue
private Node last; // end of queue
private int n; // number of elements on queue
// TODO - Add a TreeMap that maps a price to the node before that price in the queue
// and maps the first price (nothing before it) to null. You will need to
// maintain this invariant on the TreeMap.
//
// NOTE1: You will use the TreeMap to improve the running time of enqueue and delete
// so that they run in logarithmic time.
//
// NOTE2: Because you add a new field (the TreeMap), you need to consider how ALL
// the methods in the PriceQueue class might need to change in order to
// correctly maintain the invariants on the TreeMap.

// helper linked list class
private static class Node {
private Price price;
private Node next;
}

/**
* Initializes an empty queue.
*/
public PriceQueue() {
first = null;
last = null;
n = 0;
}

/**
* Returns true if this queue is empty.
*
* @return {@code true} if this queue is empty; {@code false} otherwise
*/
public boolean isEmpty() {
return first == null;
}

/**
* Returns the number of Prices in this queue.
*
* @return the number of Prices in this queue
*/
public int size() {
return n;
}

/**
* Returns the Price least recently added to this queue.
*
* @return the Price least recently added to this queue
* @throws NoSuchElementException if this queue is empty
*/
public Price peek() {
if (isEmpty()) throw new NoSuchElementException("Queue underflow");
return first.price;
}

/**
* Adds a Price to the front of the queue if it is not already present
* in the queue.
*
* @param price the Price to be added
* @return {@code true} if the Price was added and {@code false} if it was
* not added (it was already present in the queue).
*/
public boolean enqueue(Price price) {
for(Price p : this)
if (p.equals(price))
return false;
Node oldlast = last;
last = new Node();
last.price = price;
last.next = null;
if (isEmpty()) first = last;
else oldlast.next = last;
n++;
return true;
}

/**
* Removes and returns the Price in this queue that was least recently added.
*
* @return the Price on this queue that was least recently added
* @throws NoSuchElementException if this queue is empty
*/
public Price dequeue() {
if (isEmpty()) throw new NoSuchElementException("Queue underflow");
Price price = first.price;
first = first.next;
n--;
if (isEmpty()) last = null; // to avoid loitering
return price;
}


/**
* Deletes a Price from the queue if it was present.
*
* @param price the Price to be deleted.
* @return {@code true} if the Price was deleted and {@code false} otherwise
*/
public boolean delete(Price price) {
if (first == null)
return false;
if (first.price.equals(price)) {
first = first.next;
n--;
if (first == null)
last = null;
return true;
}
Node current = first;
while (current.next != null && !current.next.price.equals(price))
current = current.next;
if (current.next == null)
return false;
current.next = current.next.next;
n--;
if (current.next == null)
last = current;
return true;
}


/**
* Returns an iterator that iterates over the Prices in this queue in FIFO order.
*
* @return an iterator that iterates over the Prices in this queue in FIFO order
*/
public Iterator iterator() {
return new PriceListIterator(first);
}

// an iterator, doesn't implement remove() since it's optional
private class PriceListIterator implements Iterator {
private Node current;

public PriceListIterator(Node first) {
current = first;
}

public boolean hasNext() { return current != null; }
public void remove() { throw new UnsupportedOperationException(); }

public Price next() {
if (!hasNext()) throw new NoSuchElementException();
Price price = current.price;
current = current.next;
return price;
}
}
}

Answer rating: 100% (QA)

To implement the TreeMap as specified in the comments we need to add a TreeMap field to the PriceQueue class and adjust the methods accordingly Heres the modified PriceQueue class with the TreeMap imp... View the full answer