package edu.princeton.cs.algs4.ch13;
import edu.princeton.cs.introcs.*;
/*************************************************************************
* Compilation: javac ResizingArrayQueue.java
* Execution: java ResizingArrayQueue < input.txt
* Data files: http://algs4.cs.princeton.edu/13stacks/tobe.txt
*
* Queue implementation with a resizing array.
*
* % java ResizingArrayQueue < tobe.txt
* to be or not to be (2 left on queue)
*
*************************************************************************/
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* The <tt>ResizingArrayQueue</tt> class represents a first-in-first-out (FIFO)
* queue of generic items.
* It supports the usual <em>enqueue</em> and <em>dequeue</em>
* operations, along with methods for peeking at the first item,
* testing if the queue is empty, and iterating through
* the items in FIFO order.
* <p>
* This implementation uses a resizing array, which double the underlying array
* when it is full and halves the underlying array when it is one-quarter full.
* The <em>enqueue</em> and <em>dequeue</em> operations take constant amortized time.
* The <em>size</em>, <em>peek</em>, and <em>is-empty</em> operations takes
* constant time in the worst case.
* <p>
* For additional documentation, see <a href="http://algs4.cs.princeton.edu/13stacks">Section 1.3</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class ResizingArrayQueue<Item> implements Iterable<Item> {
private Item[] q; // queue elements
private int N = 0; // number of elements on queue
private int first = 0; // index of first element of queue
private int last = 0; // index of next available slot
/**
* Initializes an empty queue.
*/
public ResizingArrayQueue() {
// cast needed since no generic array creation in Java
q = (Item[]) new Object[2];
}
/**
* Is this queue empty?
* @return true if this queue is empty; false otherwise
*/
public boolean isEmpty() {
return N == 0;
}
/**
* Returns the number of items in this queue.
* @return the number of items in this queue
*/
public int size() {
return N;
}
// resize the underlying array
private void resize(int max) {
assert max >= N;
Item[] temp = (Item[]) new Object[max];
for (int i = 0; i < N; i++) {
temp[i] = q[(first + i) % q.length];
}
q = temp;
first = 0;
last = N;
}
/**
* Adds the item to this queue.
* @param item the item to add
*/
public void enqueue(Item item) {
// double size of array if necessary and recopy to front of array
if (N == q.length) resize(2*q.length); // double size of array if necessary
q[last++] = item; // add item
if (last == q.length) last = 0; // wrap-around
N++;
}
/**
* Removes and returns the item on this queue that was least recently added.
* @return the item on this queue that was least recently added
* @throws java.util.NoSuchElementException if this queue is empty
*/
public Item dequeue() {
if (isEmpty()) throw new NoSuchElementException("Queue underflow");
Item item = q[first];
q[first] = null; // to avoid loitering
N--;
first++;
if (first == q.length) first = 0; // wrap-around
// shrink size of array if necessary
if (N > 0 && N == q.length/4) resize(q.length/2);
return item;
}
/**
* Returns the item least recently added to this queue.
* @return the item least recently added to this queue
* @throws java.util.NoSuchElementException if this queue is empty
*/
public Item peek() {
if (isEmpty()) throw new NoSuchElementException("Queue underflow");
return q[first];
}
/**
* Returns an iterator that iterates over the items in this queue in FIFO order.
* @return an iterator that iterates over the items in this queue in FIFO order
*/
public Iterator<Item> iterator() {
return new ArrayIterator();
}
// an iterator, doesn't implement remove() since it's optional
private class ArrayIterator implements Iterator<Item> {
private int i = 0;
public boolean hasNext() { return i < N; }
public void remove() { throw new UnsupportedOperationException(); }
public Item next() {
if (!hasNext()) throw new NoSuchElementException();
Item item = q[(i + first) % q.length];
i++;
return item;
}
}
/**
* Unit tests the <tt>ResizingArrayQueue</tt> data type.
*/
public static void main(String[] args) {
ResizingArrayQueue<String> q = new ResizingArrayQueue<String>();
while (!StdIn.isEmpty()) {
String item = StdIn.readString();
if (!item.equals("-")) q.enqueue(item);
else if (!q.isEmpty()) StdOut.print(q.dequeue() + " ");
}
StdOut.println("(" + q.size() + " left on queue)");
}
}
/*************************************************************************
* Copyright 2002-2012, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4-package.jar, which accompanies the textbook
*
* Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
* Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
* http://algs4.cs.princeton.edu
*
*
* algs4-package.jar is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* algs4-package.jar is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with algs4-package.jar. If not, see http://www.gnu.org/licenses.
*************************************************************************/