Queue Deque and Priority Queue Implementations Chapter 11

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Queue, Deque, and Priority Queue Implementations Chapter 11 Copyright © 2012 by Pearson Education,

Queue, Deque, and Priority Queue Implementations Chapter 11 Copyright © 2012 by Pearson Education, Inc. All rights reserved

Contents • A Linked Implementation of a Queue • An Array-Based Implementation of a

Contents • A Linked Implementation of a Queue • An Array-Based Implementation of a Queue § A Circular Array with One Unused Location • A Vector-Based Implementation of a Queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Contents • Circular Linked Implementations of a Queue § A Two-Part Circular Linked Chain

Contents • Circular Linked Implementations of a Queue § A Two-Part Circular Linked Chain • Java Class Library: The Class Abstract. Queue • A Doubly Linked Implementation of a Deque • Possible Implementations of a Priority Queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Objectives • Implement ADT queue by using chain of linked nodes, an array, or

Objectives • Implement ADT queue by using chain of linked nodes, an array, or vector • Add or delete nodes at either end of chain of doubly linked nodes • Implement ADT deque by using chain of doubly linked nodes • Implement ADT priority queue by using array or chain of linked nodes Copyright © 2012 by Pearson Education, Inc. All rights reserved

Linked Implementation of a Queue • Consider chain of linked nodes § Head reference

Linked Implementation of a Queue • Consider chain of linked nodes § Head reference insufficient § Must also have tail reference • Which should be front of queue? § Head easier to be front of queue for entry removal § Adding entries at tail/back of queue easily done Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -1 A chain of linked nodes that implements a queue Copyright ©

Figure 11 -1 A chain of linked nodes that implements a queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Linked Implementation of a Queue • Note code for linked Implementation Listing 11 -1

Linked Implementation of a Queue • Note code for linked Implementation Listing 11 -1 Note: Code listing files must be in same folder as Power. Point files for links to work Figure 11 -2 (a) Before adding a new node to an empty chain; (b) after adding it Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -3 (a) Before, (b) during, and (c) after adding a new node

Figure 11 -3 (a) Before, (b) during, and (c) after adding a new node to the end of a nonempty chain that has a tail reference Copyright © 2012 by Pearson Education, Inc. All rights reserved

FIGURE 11 -4 (a) A queue of more than one entry; (b) after removing

FIGURE 11 -4 (a) A queue of more than one entry; (b) after removing the entry at the front of the queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -5 (a) A queue of one entry; (b) after removing the entry

Figure 11 -5 (a) A queue of one entry; (b) after removing the entry at the front of the queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Array-Based Implementation of a Queue • Listing 11 -2 : Array named queue, §

Array-Based Implementation of a Queue • Listing 11 -2 : Array named queue, § queue[0] is front § front. Index, back. Index are indices of front and back of queue • Now to decide … § With queue[0] always as front, must shift elements § Instead, move front. Index § Then we run off the end of the array!? Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -6 An array that represents a queue without moving any entries: (a)

Figure 11 -6 An array that represents a queue without moving any entries: (a) initially; (b) after removing the entry at the front twice; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -6 An array that represents a queue without moving any entries: (c)

Figure 11 -6 An array that represents a queue without moving any entries: (c) after several more additions and removals; (d) after two additions that wrap around to the beginning of the array; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Array-Based Implementation of a Queue • Solution: “Circular” array § First location follows last

Array-Based Implementation of a Queue • Solution: “Circular” array § First location follows last § Increment pointers with modulo operator back. Index = (back. Index + 1) % queue. length; front. Index = (front. Index + 1) % queue. length; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -6 An array that represents a queue without moving any entries: (a)

Figure 11 -6 An array that represents a queue without moving any entries: (a) initially; (b) after removing the entry at the front twice; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -6 An array that represents a queue without moving any entries: (c)

Figure 11 -6 An array that represents a queue without moving any entries: (c) after several more additions and removals; (d) after two additions that wrap around to the beginning of the array Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -7 A circular array that represents a queue: (a) when full; (b)

Figure 11 -7 A circular array that represents a queue: (a) when full; (b) after removing two entries; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -7 A circular array that represents a queue: (c) after removing three

Figure 11 -7 A circular array that represents a queue: (c) after removing three more entries; (d) after removing all but one entry; (e) after removing the remaining entry Copyright © 2012 by Pearson Education, Inc. All rights reserved

Circular Array with One Unused Element • Allows detection of empty vs. full queue

Circular Array with One Unused Element • Allows detection of empty vs. full queue § Examine front. Index, back. Index Figure 11 -8 A seven-location circular array that contains at most six entries of a queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -8 A seven-location circular array that contains at most six entries of

Figure 11 -8 A seven-location circular array that contains at most six entries of a queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -8 A seven-location circular array that contains at most six entries of

Figure 11 -8 A seven-location circular array that contains at most six entries of a queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -9 An array-based queue: (a) initially; (b) after removing its front entry

Figure 11 -9 An array-based queue: (a) initially; (b) after removing its front entry by incrementing front. Index; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -9 An array-based queue(c) after removing its front entry by setting queue[front.

Figure 11 -9 An array-based queue(c) after removing its front entry by setting queue[front. Index] to null and then incrementing front. Index Copyright © 2012 by Pearson Education, Inc. All rights reserved

Vector-Based Implementation of a Queue • Front of queue at beginning of vector •

Vector-Based Implementation of a Queue • Front of queue at beginning of vector • Vector add method used at back of queue • Remove from front of queue § Vector takes care of moving elements § No indices needed • Vector manages additional space as needed • View Listing 11 -3 Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -11 A vector that represents a queue Copyright © 2012 by Pearson

Figure 11 -11 A vector that represents a queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Circular Linked Implementations of a Queue Figure 11 -12 A circular linked chain with

Circular Linked Implementations of a Queue Figure 11 -12 A circular linked chain with an external reference to its last node that (a) has more than one node; (b) has one node; (c) is empty Copyright © 2012 by Pearson Education, Inc. All rights reserved

Two-Part Circular Linked Chain Figure 11 -13 A two-part circular linked chain that represents

Two-Part Circular Linked Chain Figure 11 -13 A two-part circular linked chain that represents both a queue and the nodes available to the queue Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -14 A two-part circular linked chain that represents a queue: (a) when

Figure 11 -14 A two-part circular linked chain that represents a queue: (a) when it is empty; (b) after adding one entry; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -14 A two-part circular linked chain that represents a queue: (c) after

Figure 11 -14 A two-part circular linked chain that represents a queue: (c) after adding three more entries; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -14 A two-part circular linked chain that represents a queue: (d) after

Figure 11 -14 A two-part circular linked chain that represents a queue: (d) after removing the front entry; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -14 A two-part circular linked chain that represents a queue: (e) after

Figure 11 -14 A two-part circular linked chain that represents a queue: (e) after adding one more entry Copyright © 2012 by Pearson Education, Inc. All rights reserved

Two-Part Circular Linked Chain • Outline of the class, Listing 11 -4 Figure 11

Two-Part Circular Linked Chain • Outline of the class, Listing 11 -4 Figure 11 -15 A chain that requires a new node for an addition to a queue: (a) before the addition; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -15 A chain that requires a new node for an addition to

Figure 11 -15 A chain that requires a new node for an addition to a queue: (b) after the addition Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -16 (a) A chain with nodes available for additions to a queue;

Figure 11 -16 (a) A chain with nodes available for additions to a queue; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -16 (b) the chain after one addition; Copyright © 2012 by Pearson

Figure 11 -16 (b) the chain after one addition; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -16 (c) the chain after another addition; Copyright © 2012 by Pearson

Figure 11 -16 (c) the chain after another addition; Copyright © 2012 by Pearson Education, Inc. All rights reserved

Java Class Library: The Class Abstract. Queue • Methods provided § public boolean add(T

Java Class Library: The Class Abstract. Queue • Methods provided § public boolean add(T new. Entry) § public boolean offer(T new. Entry) § public T remove() § public T poll() § public T element() § public T peek() § public boolean is. Empty() § public void clear() § public int size() Copyright © 2012 by Pearson Education, Inc. All rights reserved

Doubly Linked Implementation of a Deque • Problem: each node in a chain references

Doubly Linked Implementation of a Deque • Problem: each node in a chain references only the next node. § We need to be able to move backward from a node • This suggests a doubly linked chain Copyright © 2012 by Pearson Education, Inc. All rights reserved

Doubly Linked Implementation of a Deque • View implementation, Listing 11 -5 Figure 11

Doubly Linked Implementation of a Deque • View implementation, Listing 11 -5 Figure 11 -17 A doubly linked chain with head, tail references Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -18 Adding to the back of a nonempty deque: (a) after the

Figure 11 -18 Adding to the back of a nonempty deque: (a) after the new node is allocated; (b) after the addition is complete Copyright © 2012 by Pearson Education, Inc. All rights reserved

Figure 11 -19 (a) A deque containing at least two entries; (b) after removing

Figure 11 -19 (a) A deque containing at least two entries; (b) after removing the first node and obtaining a reference to the deque’s new first entry Copyright © 2012 by Pearson Education, Inc. All rights reserved

Possible Implementations of a Priority Queue Figure 11 -20 Two possible implementations of a

Possible Implementations of a Priority Queue Figure 11 -20 Two possible implementations of a priority queue using (a) an array; (b) a chain of linked nodes Copyright © 2012 by Pearson Education, Inc. All rights reserved

End Chapter 11 Copyright © 2012 by Pearson Education, Inc. All rights reserved

End Chapter 11 Copyright © 2012 by Pearson Education, Inc. All rights reserved

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