GROUP MEMBERSNames Roll No.Fatima Saqib 39Bilal Younus 10Areesha Butt 58Muhammad Fahim 42Poshma Kiyani 02Abdur Rehman 41

Presentation Topic

Queue

QUEUEA queue is two ended data structure in which items can be inserted from one end and taken out from the other end. Therefore , the first item inserted into queue is the first item to be taken out from the queue. This property is called First in First out [FIFO].e.g: the picture given below:

Queue Example ● A queue of people in the bank who are trying to submit utility bills. ● A line of vehicle on the motorway toll plaza. ● Consider a shared printer in a computer laboratory. Student can send their print request to the printer and each print request goto queue and serve one by one. ● Computer input operations performing through mouse and keyboard are also recorded into queue and serve on the basis of FIFO.

QUEUE example

Deque stands for double-end queueA data structure in which elements can be added or deleted at either the front or rear.But no changes can be made in the listDeque is generalization of both stack and queue.

Deque

Variations In Deque:

There are two variations of a deque. Input Restricted Deque Output Restricted Deque

An input restricted deque restricts the insertion of elements at one end only, but the deletion of elements can perform at

both the ends.

Input Restricted Deque

An output restricted queue, restricts the deletion of elements at one end only, and

allows insertion to be done at both the ends of deque

Output Restricted Deque

Possibilities The two possibilities that must be considered while inserting or deleting elements into the queue are : When an attempt is made to insert an element into a deque which is already full, an overflow occurs. When an attempt is made to delete an element from a deque which is empty, underflow occurs

Deque

The Queue Operations• A queue is like a line of people

waiting for a bank teller. The queue has a front and a rear.

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Front

Rear

The Queue Operations

• New people must enter the queue at the rear. • The C++ queue class calls this a push,

although it is usually called an enqueue operation.

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FrontRear

The Queue Operations

• When an item is taken from the queue, it always comes from the front. The C++ queue calls this a pop, although it is usually called a dequeue operation.

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FrontRear

Function of Queue REAR FRONT APPEND SERVE IsEmpty IsFull

RearRear is the tail/bottom of the queue. The

entry at rear is the most recently arrived item and must wait until the other entries are

present in the queue.

Insert (Enqueue)

Remove(Dequeu) rearfront

FRONTFront is the position from where items can be

taken out from queue. It is also termed as head or top of the queue. The entry at the

front position is ready to be served

Insert (Enqueue)

Remove(Dequeu) rearfront

APPENDThe operation to add an item at the rear

position of the queue is termed as append or enqueue. We can append items at the rear position of the queue until the queue is not full. The rear points towards the position

where new item has been appended.

17 23 97 44 333After insertion:

17 23 97 44Initial queue:

Serve The operation to remove an item from the front position of the queue is termed as

serve or dequeue. We can serve the items in the queue until the queue is not empty. The front points towards the position from where

the available item can be severed

SERVE

Queue is consider empty when there is no item on front of the queue. IsEmpty operation checks for this condition and return true if the queue is empty else

return false.

IsEmpty

0 1 2 3 4 5 6 7myQueue:

If no element can be appended at rear of

the queue then queue consider as full. When rear of the queue reaches this limit, then queue is full and the IsFull operation

return true else return false

IsFull

44 55 66 77 88 11 22 33

0 1 2 3 4 5 6 7myQueue:

Array Implementation of Queue• When enqueuing, the front index is always fixed and

the rear index moves forward in the array.• There are several different algorithms to implement

Enqueue and Dequeue

front

rear

Enqueue(3)

3

front

rear

Enqueue(6)

3 6

front

rear

Enqueue(9)

3 6 9

Queue Implementation of Array• When enqueuing, the front index is always fixed

and the rear index moves forward in the array.• When dequeuing, the element at the front of the

queue is removed. Move all the elements after it by one position.

Dequeue()

front

rear

6 9

Dequeue() Dequeue()

front

rear

9

rear = -1

front

Queue Implementation of Array

• Better way• When an item is enqueued, make the rear

index move forward.• When an item is dequeued, the front index

moves by one element towards the back of the queue (thus removing the front item).

Array Implementation....• A queue can be implemented with an array.

For example, this queue contains the integers 4 (at the front), 8 and 6 (at the rear).

[ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ] . ..

An array of integers to implement a queue of integers

4 8 6

Array Implementation....• The easiest implementation also

keeps track of the number of items in the queue and the index of the first element (at the front of the queue), the last element (at the rear).

[ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ] . . .

4 8 6

size3

first0

last2

..Array implementation of queues

• A queue is a first in, first out (FIFO) data structure• This is accomplished by inserting at one end (the

rear) and deleting from the other (the front)

• To insert: put new element in location 4, and set rear to 4

• To delete: take element from location 0, and set front to 1

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17 23 97 44

0 1 2 3 4 5 6 7myQueue:

rear = 3front = 0

…Array implementation of queues

• Notice how the array contents “crawl” to the right as elements are inserted and deleted

• This will be a problem after a while!

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17 23 97 44 333After insertion:

23 97 44 333After deletion:

rear = 4front = 1

17 23 97 44Initial queue:

rear = 3front = 0

Representation of queue by program

• How to insert Value• How to delete value• How to print value• Complete Program Example

To Insert ValueAlgorithm:R=F=-1 IF R >= SIZE THEN

PRINT ‘’Overflow’’RETURN

ELSE {R=R+1 [Insert Item]

Q[R]=‘’item’’ IF F=-1 THEN F=0 } END IF

Algorithm: If ( FRONT = -1 ) then print "Queue is empty" Exit Else ITEM = Que [ FRONT ] If ( FRONT = REAR ) REAR = -1 FRONT = -1 Else FRONT = FRONT + 1 Stop

To Delete Value

Main body of program

Class of the program

Main body of program Output

ThanksYes, finished