ADTs Stack and Queue. Outline

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1 Chapter 5 ADTs Stack and Queue Fall 2017 Yanjun Li CS Outline Stack Array-based Implementation Linked Implementation Queue Array-based Implementation Linked Implementation Comparison Fall 2017 Yanjun Li CS2200 2

2 Queues Fall 2017 Yanjun Li CS Queues Fall 2017 Yanjun Li CS2200 4

3 Queues What do these composite objects all have in common? Fall 2017 Yanjun Li CS Queue Queues An abstract data type in which elements are added to the rear and removed from the front; a first in, first out (FIFO) structure Fall 2017 Yanjun Li CS2200 6

4 Queues What operations would be appropriate for a queue? Fall 2017 Yanjun Li CS Queues Transformers MakeEmpty Enqueue Dequeue Observers IsEmpty IsFull change state observe state What about an iterator? Fall 2017 Yanjun Li CS2200 8

5 Queues For what type of problems would queues be useful? Print server maintains a queue of print jobs. Disk driver maintains a queue of disk input/output requests. Scheduler (e.g., in an operating system) maintains a queue of processes awaiting a slice of machine time. Fall 2017 Yanjun Li CS Queues class QueueType Logical Level public: QueueType(int max); QueueType(); ~QueueType(); bool IsEmpty() const; bool IsFull() const; void Enqueue(ItemType item); //add newitem to the rear of the queue. void Dequeue(ItemType& item); //remove front item from queue Fall 2017 Yanjun Li CS

6 Array-Based Implementation private: ItemType* items; // Dynamically allocated array int maxque; // Whatever else we need ; Implementation level Fall 2017 Yanjun Li CS Array-Based Implementation One data structure: An array with the front of the queue fixed in the first position Enqueue A, B, C, D Dequeue Move elements forward What s wrong with this design? Fall 2017 Yanjun Li CS

7 Array-Based Implementation Another data structure: An array where the front floats What happens if we add X, Y, and Z? Fall 2017 Yanjun Li CS Array-Based Implementation We can let the queue wrap around in the array; i.e. treat the array as a circular structure Fall 2017 Yanjun Li CS

8 Array-Based Implementation (a) Initial conditions A [0] [1] [2] [3] [4] (b) queue.dequeue(item) [0] [1] [2] [3] [4] front = 2 rear = 2 front = 3 rear = 2 Empty Queue Full Queue How can we tell the difference? Fall 2017 Yanjun Li CS Array-Based Implementation A third data structure:front indicates the slot preceding the front item;it is reserved and not used Empty Queue Full Queue Fall 2017 Yanjun Li CS

9 Array-Based Implementation private: int front; int rear; int maxque; Complete implementation level ItemType* items; ; To what do we initialize front and rear? Fall 2017 Yanjun Li CS Array-Based Implementation QueueType::QueueType( int max) maxque = max + 1; front = maxque - 1; rear = maxque - 1; items = new ItemType[maxQue]; QueueType::QueueType( ) maxque = ; front = maxque - 1; rear = maxque - 1; items = new ItemType[maxQue]; Why is the array declared max + 1? QueueType::~QueueType( ) delete [] items; Fall 2017 Yanjun Li CS

10 Array-Based Implementation //Pre: the queue is not full //Post: newitem is at the rear of the queue void QueueType::Enqueue(ItemType newitem) if (IsFull()) throw FullQueue(); else rear = (rear+1)%maxque; items[rear] = newitem; Fall 2017 Yanjun Li CS Array-Based Implementation //pre: the queue is not empty //post: the front of the queue has been removed // and a copy returned in item void QueueType::Dequeue(ItemType& item) if (IsEmpty()) throw EmptyQueue(); else front = (front+1)%maxque; item = items[front]; Fall 2017 Yanjun Li CS

11 Array-Based Implementation //returns true if the queue is empty bool QueueType::IsEmpty( ) return ( rear == front ); //returns true if the queue is full bool QueueType::IsFull( ) return ( (rear + 1) % maxque == front ) Fall 2017 Yanjun Li CS Counted Queue Counted Queue A queue that has an additional function GetLength that returns the number of items in the queue What functions must be defined in class CountedQue? Fall 2017 Yanjun Li CS

12 Counted Queue class CountedQueueType : public QueueType public: CountedQueueType(); void Enqueue(ItemType newitem); void Dequeue(ItemType& item); int GetLength( ) const; private: int length; ; Fall 2017 Yanjun Li CS Counted Queue Fall 2017 Yanjun Li CS

13 Counted Queue void CountedQueueType::Enqueue(ItemType newitem) What is this? try QueueType::Enqueue(newItem); length++; catch(fullqueue e) throw FullQueue(); Why must the call to Enqueue be embedded within a try/catch statement? Fall 2017 Yanjun Li CS Counted Queue Does the derived class have access to the base class s private data members in C++? Exercise: finish Counted Queue Implementation. Fall 2017 Yanjun Li CS

14 Linked Implementation Data structure for linked queue What data members are needed? Fall 2017 Yanjun Li CS Linked Implementation Enqueue(newItem) Set newnode to the address of newly allocated node Set Info(newNode) to newitem Set Next(newNode) to NULL If queue is empty Set front to newnode else Set Next(rear) to newnode Set rear to newnode Fall 2017 Yanjun Li CS

15 Linked Implementation Dequeue(item) Set tempptr to front Set item to Info(front) Set front to Next(front) if queue is now empty Set rear to NULL Deallocate Node(tempPtr) Fall 2017 Yanjun Li CS Storage Requirements What does this table tell you? Fall 2017 Yanjun Li CS

16 Reference Reproduced from C++ Plus Data Structures, 4 th edition by Nell Dale. Reproduced by permission of Jones and Bartlett Publishers International. Fall 2017 Yanjun Li CS

Propedéutico de Programación

Propedéutico de Programación Coordinación de Ciencias Computacionales Semana 4, Tercera Parte Dra. Pilar Gómez Gil Versión 1.1 01.07.08 http://ccc.inaoep.mx/~pgomez/cursos/programacion/ Capítulo 5 ADT