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Queues, Deques, and Priority Queues

Queues, Deques, and Priority Queues. Chapter 22. 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

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Queues, Deques, and Priority Queues

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  1. Queues, Deques, and Priority Queues Chapter 22

  2. 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 • Specifications of the ADT Deque • 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

  3. 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

  4. Specifications for the ADT Queue Fig. 22-1 Some everyday queues.

  5. Specifications for the ADT Queue • Interface for a queue of objects public interface queueInterface{ /** Task: Adds a new entry to the back of the queue. * @param newEntry an object to be added */public void enqueue(Object newEntry); /** Task: Removes and returns the front of the queue. * @return either the object at the front of the queue or null if the queue was empty */public Object dequeue(); /** Task: Retrieves the front of the queue. * @return either the object at the front of the queue or null if the queue is empty */public Object getFront(); /** Task: Determines whether the queue is empty. * @return true if the queue is empty */public boolean isEmpty(); /** Task: Removes all entries from the queue. */public void clear();} // end queueInterface

  6. Specifications for the ADT Queue Fig. 22-2 Queue of strings after (a) enqueue adds Jim; (b) Jess; (c) Jill; (d) Jane; (e) Joe; (f) dequeue retrieves, removes Jim; (g) enqueue adds Jerry; (h) dequeue retrieves, removes Jess.

  7. Using a Queue to Simulate a Waiting Line Fig. 22-3 A line, or queue of people.

  8. Classes WaitLine and Customer Fig. 22-4 A CRC card for the class WaitLine.

  9. Classes WaitLine and Customer Fig. 22-5 A diagram of the classes WaitLine and Customer.

  10. Classes WaitLine and Customer Fig. 22-6 A simulated waiting line … continued →

  11. Classes WaitLine and Customer Fig. 22-6 (ctd) A simulated waiting line.

  12. 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

  13. Classes StockLedger and StockPurchase Fig. 22-7 A CRC card for the class StockLedger

  14. Classes StockLedger and StockPurchase Fig. 22-8 A diagram of the class StockLedger and StockPurchase.

  15. Classes StockLedger and StockPurchase Fig. 22-9 A queue of (a) individual shares of stock; (b) grouped shares.

  16. 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

  17. Specifications of the ADT Deque Fig. 22-10 An instance of a deque.

  18. Specifications of the ADT Deque • A Java interface public interface DequeInterface{ public void addToFront(Object newEntry);public void addToBack(Object newEntry);public Object removeFront();public Object removeBack();public Object getFront();public Object getBack();public boolean isEmpty();public void clear();} // end DequeInterface

  19. Specifications of the ADT Deque Fig. 22-11 A comparison of the operations that add, remove, and retrieve the entries of a stack s, queue q, and a deque d; (a) add; (b) remove; (c) retrieve.

  20. 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

  21. 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

  22. Specifications of the ADT Priority Queue public interface PriorityQueueInterface{ public void add(Comparable newEntry); public Comparable remove();public Comparable get();public boolean isEmpty();public int getSize();public void clear();} // end PriorityQueueInterface

  23. Using Priority Queue to Compute Capital Gain in Sale of Stock • Revise class StockPurchase • Include data field date • Method compareTo is made available • This field is the priority – earliest date is highest priority

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