Brief description of Queue and its types. Easy and helpful to clear the doubts regarding the Topic.Come and Try .

2. TOPIC:
QUEUESQuooooooooooooooos……………………

3. Contents:
• Introduction to Queues
• Basic features of Queues
• Operations on Queues
• Algorithms and representation of Queues
• Types of Queues
• Applications of Queues
• How Queue is different from Stack?
• References

4. DATA STRUCTURE
▪Data structure is a way of organization
of all data items that considers not only
the elements stored but also their
relationship to each other.
▪Data structure is a specialized format
for organizing and storing data.
▪Ex. English Dictionary (sorted words).

5. TYPE OF DATA STRUCTURE

6. QUEUE
S:
▪ Queue is Non- primitive Linear Data
structure.
▪ Queue is also an abstract data type(ADT).
▪ In queue the first element is inserted from
one end called REAR(also called tail).
▪ The deletion of existing element takes
place from the other end called as
FRONT(also called head).

7. BASIC FEATURES OF
QUEUE:
• Like Stack, Queue is also an ordered list of
elements of similar data types.
i.e. It is a collection of homogeneous elements.
• Queue is a FIFO( First in First Out ) structure.
i.e. - the element which is inserted first will be
removed first.
- the middle elements are logically
inaccessible.
• Queue is used for temporary storage of data
values.

9. OPERATIONS ON QUEUE:
Basic Operations:
• Queue operations may involve initializing or defining
the queue, utilizing it, and then completely erasing it
from the memory.
• Queue operations involve basically two main
operations as follows:

10. • enqueue() − add (store) an item to the queue.
For enqueing (or storing) data in the queue we take
help of rear pointer.
•dequeue() − remove (access) an item from the queue.
In queue, we always dequeue (or access) data, pointed
by front pointer.
•Init() - This function is used for initializing the queue.
•Front – This is used to get the front data item from the
queue.
•Rear - This is used to get the last data item from the
queue.

12. ALGORITHMS
OF
QUEUES

13. •.
• Queue can be implemented using an
Array, Stack or Linked List.
• The easiest way of implementing a queue
is by using an Array.
• Initially the head(FRONT) and the
tail(REAR) of the queue points at the first
index of the array (starting the index of
array from 0).

14. Conditions in Queue
• FRONT < 0 ( Queue is Empty )
• REAR = Size of Queue ( Queue is Full )
• FRONT < REAR ( Queue contains at least one
element )
• No of elements in queue is : ( REAR - FRONT ) +
1
Restriction in Queue
•We can not insert element directly at middle index
(position) in Queue and vice verse for deletion.
• Insertion operation possible at REAR end only and
deletion operation at FRONT end. To insert we
increment REAR and to delete we increment
FRONT.

15. Enqueue Operation:
The following steps should be taken to enqueue (insert)
data into a queue −
•Step1− Check if the queue is full.
•Step2− If the queue is full, produce overflow error and
exit.
•Step3− If the is not full increment the rear pointer
to point the next empty space.
•Step4− Add data element to the queue location, where
the rear is pointing.
•Step5− return success.

16. Procedure enqueue(data)
if queue is full
return overflow
endif
rear ← rear + 1
queue[rear] ← data
return true
end procedure
int enqueue(int data)
if(isfull())
return 0;
rear = rear + 1;
queue[rear] = data;
return 1;
end procedure
ALGORITH
M:
IMPLEMENTATIO
N :

17. The following steps are taken to perform dequeue
operation −
•Step 1 − Check if the queue is empty.
•Step 2 − If the queue is empty, produce underflow
error and exit.
•Step 3 − If the queue is not empty, access the data
where front is pointing.
•Step 4 − Increment front pointer to point to the next
available data element.
•Step 5 − Return success.
Dequeue Operation:

18. procedure dequeue
if queue is empty
return underflow
end if
data = queue[front]
front ← front + 1
return true
end procedure
int dequeue()
{
if(isempty())
return 0;
int data = queue[front];
front = front + 1;
return data;
}
Algorithm: Implementation:

19. Program to implement Queue using Array:
#include<stdio.h>
#include<conio.h>
#define SIZE 10
void enQueue(int);
void deQueue();
void display();
int queue[SIZE], front = -1, rear = -1;
void main()
{
int value, choice;
clrscr();
while(1){
printf("nn***** MENU *****n");
printf("1.Insertion n2.Deletion n3.Display n4.Exit“);
printf("nEnter your choice: ");
scanf("%d",&choice);
switch(choice){

20. case 1: printf("Enter the value to be insert: ");
scanf("%d",&value);
enQueue(value);
break;
case 2: deQueue();
break;
case 3: display();
break;
case 4: exit(0);
default: printf("nWrong selection!!! Try again!!!");
}
}
}
void enQueue(int value){
if(rear == SIZE-1)
printf("nQueue is Full!!! Insertion is not possible!!!");
else{
if(front == -1)
front = 0;
rear++;
queue[rear] = value;
printf("nInsertion success!!!");

21. }
}
void deQueue(){
if(front == rear)
printf("nQueue is Empty!!! Deletion is not possible!!!");
else{
printf("nDeleted : %d", queue[front]);
front++;
if(front == rear)
front = rear = -1;
}
}
void display(){
if(rear == -1)
printf("nQueue is Empty!!!");
else{
int i;
printf("nQueue elements are:n");
for(i=front; i<=rear; i++)
printf("%dt",queue[i]);
}
}

22. Output:

23. Array Representation of
Queues:

24. Linked-List Representation
of Queues:

25. Types
of
Queue:

26. Basically there are FOUR main types of
queue, they are
as follows:
• SIMPLE QUEUE
• CIRCULAR QUEUE
• PRIORITY QUEUE
• DEQUE

27. SIMPLE QUEUE:
• Simple queue defines the simple
operation of queue in which
insertion occurs at the REAR of
the queue and deletion occurs at
the FRONT of the queue.
REAR FRONT

28. CIRCULAR QUEUE:
• Circular queue are used to remove the
drawback of simple queue.
• Both the front and the rear pointers
wrap around to the beginning of the array.
• It is also called as “RING BUFFER”.
• It is an ADT (abstract data type) .

29. PRIORITY QUEUE:
• Priority queue is the collection of elements
where elements are stored according to their
priority levels.
• Inserting and deleting of elements from queue
is decided by the priority of the elements.
• An element of higher priority is processed first.
• The two elements of same priority is processed
on FCFS (First come First served )basis.

30. • An example of priority queue in computer
science occurs in timesharing system in which
the processes of higher priority is executed
before any process of lower priority.
•
There are two types of priority queue:
• Ascending priority queue : It is a collection of
items in to which items can be inserted arbitrarily
and from which only the smallest item can be
removed.
• Descending priority queue : It is similar but
allows deletion of only the largest item.

31. DEQUE QUEUE:
• Deque stands for double ended queue.
• Also known as head–tail linked list.
• Elements can be deleted or inserted at
either end.

32. TYPES OF DEQUE:
•Input restricted deques : It allows insertions at only one end
of the array or list but deletions allows at both ends.
•Output restricted deques : It allows deletions at only one end
of the array or list but insertions allow at both ends.

34. In Computer Science field:
• Scheduler: for controlling access to shared
resources.
• Round Robin scheduling
• Job scheduling
• Keyboard buffer
• Print lines of a document
• Recognizing Palindromes
• Shared resource usage(CPU ,memory
access)
• Simulation

35. Shared printer Usage
Job

36. In Real Life Scenario:
• Simulation of Real World Illustrations:
- Waiting in line.
- Waiting on hold for Tech support.
- Waiting for your turn in mess-hall.
- Computer Lab.
• Telephone Operators:
- queuing system for handling calls to toll-
free numbers.

37. Queue in a Bank
Computer Lab

39. HOW QUEUE
IS
DIFFERENT
FROM STACK?

41. References:
• “ Introduction to Algorithms ”
by Thomas H.
• mycodeschool Videos
• www.w3schools.com
• www.hackerearth.com
• www.tutorialspoint.com

42. ANY
QUESTIO
NS