1. Data Structures Using C++
Chapter 8
Queues
Data Structures Using C++

2. Data Structures Using C++
Chapter Objectives
Learn about queues
Examine various queue operations
Learn how to implement a queue as an array
Learn how to implement a queue as a linked list
Data Structures Using C++

3. Data Structures Using C++
Chapter Objectives
Discover queue applications
Examine the STL class queue
Discover priority queues
Data Structures Using C++

4. Data Structures Using C++
Queues
Definition: data structure in which the elements are added at one end, called the rear, and deleted from the other end, called the front or first
First In First Out (LIFO) data structure
Data Structures Using C++

5. Basic Operations on a Queue
initializeQueue: Initializes the queue to an empty state
destroyQueue: Removes all the elements from the queue, leaving the queue empty
isEmptyQueue: Checks whether the queue is empty. If the queue is empty, it returns the value true; otherwise, it returns the value false
Data Structures Using C++

6. Basic Operations on a queue
isFullQueue: Checks whether the queue is full. If the queue is full, it returns the value true; otherwise, it returns the value false
front: Returns the front (first) element of the queue; the queue must exist
back: Returns the front (first) element of the queue; the queue must exist
Data Structures Using C++

7. Basic Operations on a queue
addQueue: Adds a new element to the rear of the queue; the queue must exist and must not be full
deleteQueue: Removes the front element of the queue; the queue must exist and must not be empty
Data Structures Using C++

8. Data Structures Using C++
Queues as Arrays
Data Structures Using C++

9. Data Structures Using C++
Queues as Arrays
Data Structures Using C++

10. Data Structures Using C++
Circle Queue
Data Structures Using C++

11. Data Structures Using C++
Queues as Arrays
Data Structures Using C++

12. Data Structures Using C++
Queues as Arrays
Data Structures Using C++

13. Data Structures Using C++
Queues as Arrays
Data Structures Using C++

14. Data Structures Using C++
Queues as Arrays
Data Structures Using C++

15. Data Structures Using C++
Queues as Arrays
Data Structures Using C++

16. Data Structures Using C++
Queues as Arrays
Data Structures Using C++

17. Data Structures Using C++
Queues as Arrays
Data Structures Using C++

18. UML Diagram of the class queueType
Data Structures Using C++

19. Data Structures Using C++
Initialize Queue
Definition of the function initializeQueue:
template<class Type>
void queueType<Type>::initializeQueue() {
queueFront = 0;
queueRear = maxQueueSize - 1;
count = 0; }
Data Structures Using C++

20. Empty Queue and Full Queue
template<class Type>
bool queueType<Type>::isEmptyQueue() {
return (count == 0); }
bool queueType<Type>::isFullQueue()
return (count == maxQueueSize);
Data Structures Using C++

21. Data Structures Using C++
Destroy Queue
template<class Type>
void queueType<Type>::destroyQueue() {
queueFront = 0;
queueRear = maxQueueSize - 1;
count = 0; }
Data Structures Using C++

22. Data Structures Using C++
front and back
template<class Type>
Type queueType<Type>::front() {
assert(!isEmptyQueue());
return list[queueFront]; }
template<class Type>
Type queueType<Type>::back() {
assert(!isEmptyQueue());
return list[queueRear]; }
Data Structures Using C++

23. Data Structures Using C++
Add Queue
template<class Type>
void queueType<Type>::addQueue(const Type& newElement) {
if(!isFullQueue())
queueRear = (queueRear + 1) % maxQueueSize; //use the mod
//operator to advance queueRear
//because the array is circular
count++;
list[queueRear] = newElement; }
else
cerr<<"Cannot add to a full queue."<<endl;
Data Structures Using C++

24. Data Structures Using C++
Delete Queue
template<class Type>
void queueType<Type>::deleteQueue() {
if(!isEmptyQueue())
count--;
queueFront = (queueFront + 1) % maxQueueSize; //use the mod
//operator to advance queueFront
//because the array is circular }
else
cerr<<"Cannot remove from an empty queue."<<endl;
Data Structures Using C++

25. Constructor and Destructor
Creates an array of the size specified by the user
Default value is 100
Initializes queueFront queueRear to indicate that the queue is empty
Destructor
When queue object goes out of scope, destructor reallocates memory occupied by the array that stores the queue elements
Data Structures Using C++

26. Data Structures Using C++
Linked Queue as an ADT
Data Structures Using C++

27. Empty, Full, and Destroy Queue
Queue is empty if queueFront is NULL
Queue is full only if we run out of memory
Destroy queue removes all elements of the queue
Data Structures Using C++

28. Data Structures Using C++
addQueue
Adds a new element to the end of the queue
Access the pointer queueRear to implement addQueue
Data Structures Using C++

29. Front, Back, and Delete Queue
If queue is nonempty:
operation front returns the first element of the queue
operation back returns the last element of the queue
operation deleteQueue removes the first element of the queue
If queue is empty:
function front terminates the program
function back terminates the program
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30. STL class queue (Queue Container Adapter)
Data Structures Using C++

31. Data Structures Using C++
Priority Queue
FIFO rules of a queue are relaxed
Customers or jobs with higher priority are pushed to front of queue
To implement:
use an ordinary linked list, which keeps the items in order from the highest to lowest priority
use a treelike structure
Data Structures Using C++

32. Data Structures Using C++
Application of Queues
Data Structures Using C++

33. Data Structures Using C++
Application of Queues
Data Structures Using C++

34. Data Structures Using C++
Application of Queues
Data Structures Using C++

35. Application of Queues: waitingCustomerQueueType
Data Structures Using C++

36. Data Structures Using C++
Poisson Distribution
Data Structures Using C++

37. Data Structures Using C++
Chapter Summary
Queue Data Structure
Restricted Version of arrays and linked list
Basic operations
First In First Out (FIFO)
Queues Implemented as Arrays
Data Structures Using C++

38. Data Structures Using C++
Chapter Summary
Queues Implemented as Linked Lists
STL class queue
Priority Queues
Application of Queues
Data Structures Using C++