ch23v2.0

Queues, Deques, and

Priority Queues

Chapter 23

Slides by Steve ArmstrongLeTourneau University

Longview, TX2007,Prentice Hall

Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X

Chapter Contents• Specifications for the ADT Queue• Using a Queue to Simulate a Waiting Line

The Classes WaitLine and Customer

• Using a Queue to Compute the capital Gain in a Sale of Stock The Classes StockLedger and StockPurchase

• Java Class Library: the Interface Queue• Specifications of the ADT Deque


Chapter Contents

• Using a Deque to Compute the Capital Gain in a Sale of Stock

• Specifications of the ADT Priority Queue

• Using a Priority Queue to Compute the Capital Gain in a Sale of Stock

• Specifications of the ADT Priority Queue

• Using a Priority Queue to Track Your Assignments


Specifications for the ADT Queue

• Queue organizes entries according to order of entry Exhibits first-in, first-out behavior Contrast to stack which is last-in, first-out

• All additions are at the back of the queue

• Front of queue has items added first



Fig. 23-1 Some everyday queues.



• View interface for a queue of objects

• Note methods enqueue dequeue getFront isEmpty clear



Fig. 23-2 Queue of strings after (a) enqueue adds Jim;

(b) Jess; (c) Jill; (d) Jane;



Fig. 23-2 Queue of strings after (e) enqueue adds Joe; (f) dequeue retrieves, removes Jim; (g) enqueue adds

Jerry; (h) dequeue retrieves, removes Jess.


Using a Queue to Simulate a Waiting Line

Fig. 23-3 A line, or queue of people.


Classes WaitLine and Customer

Fig. 23-4 A CRC card for the class WaitLine.



Fig. 23-5 A diagram of the classes WaitLine and Customer.



Fig. 23-6 A simulated waiting line … continued →



Fig. 23-6 (ctd) A simulated waiting line.


The Class Waitline

• View source code

• Note methods Constructor simulate displayResults reset


Using a Queue to Compute Capital Gain in a Sale of Stock

• Must sell stocks in same order they were purchased Must use the difference in selling price and

purchase price to calculate capital gain

• We use a queue to Record investment transactions

chronologically Compute capital gain of the stock


Classes StockLedger and StockPurchase

Fig. 23-7 A CRC card for the class StockLedger



Fig. 23-8 A diagram of the class StockLedger and StockPurchase.



• View source code for class StockLedger

• Note method Constructor buy sell



Fig. 23-9 A queue of (a) individual shares of stock; (b) grouped shares.


Java Class Library: The Interface Queue

• Similar to our QueueInterface Specifies more methods

• Methods provided


Specifications of the ADT Deque

• A Double ended queue

• Has operations that Add, remove, or retrieve entries At both its front and back

• Combines and expands the operations of queue and stack



Fig. 23-10 An instance of a deque.



• A Java interface



Fig. 23-11 A comparison of the operations that add, remove, and retrieve the entries of a stack s, queue q,

and a deque d; (a) add;




and a deque d; (b) remove;




and a deque d; (c) retrieve.


Using a Deque to Compute Capital Gain in Sale of Stock

• Revise the class StockPurchase Represents purchase of n shares at d dollars per

share Constructor is changed Accessor methods for new fields added

• Revise class StockLedger Method ledger now an instance of a deque Method buy now creates instance of StockPurchase, places it at back of deque

Method sell also altered

Click to view new methodsClick to view new methods


Specifications of the ADT Priority Queue

• Organizes objects according to priorities Contrast to regular queue in order of arrival

• Priority queue example – a hospital ER• Priority can be specified by an integer

Must define whether high number is high priority or …

Low number (say 0) is high priority

• Other objects can specify priority Object must have a compareTo method


Specifications of the ADT Priority Queue

• Note specification for ADT priority queue

• Methods specified add remove peek getSize clear


Using Priority Queue to Track Your Assignments

• Organize class or work assignments by due dates Early due date, higher priority

• Figure 23-2 diagram of class Assignment


Using Priority Queue to Track Your Assignments

• Fig. 23-13 A diagram of the class AssignmentLog

• Note source code of class

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