Queues, Deques, and Priority Queues Chapter 23 Slides by Steve Armstrong LeTourneau University...

Queues, Deques, and

Priority Queues

Chapter 23

Slides by Steve ArmstrongLeTourneau University

Longview, TX2007,Prentice Hall

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 1

• 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

Specifications for the ADT Queue

Fig. 23-1 Some everyday queues.

• View interface for a queue of objects

• Note methods enqueue (item) add dequeue remove getFront (returns item) isEmpty clear

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

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

Specifications for the ADT Queue

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 5

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

Classes WaitLine and Customer

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

Classes WaitLine and Customer 6

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 10

• 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 11

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

Classes StockLedger and StockPurchase

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

Classes StockLedger and StockPurchase 12

• View source code for class StockLedger

• Note method Constructor buy sell

Classes StockLedger and StockPurchase

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 15

• 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

Specifications of the ADT Deque

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 17

• 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 //highest priority peek //retrieves highest priority getSize clear

Using Priority Queue to Track Your Assignments 19

• 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

Queues, Deques, and Priority Queues Chapter 23 Slides by Steve Armstrong LeTourneau University...

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