The document provides a comprehensive overview of queues, including their definition as a FIFO data structure where insertion occurs at the rear and deletion at the front. It covers various types of queues such as circular queues, double-ended queues (deques), and priority queues, as well as their applications in both real life and computer science, such as job scheduling and resource management. The document also discusses operations related to each type of queue and their specific functionalities.

1. 1

2. Index
S.No Topic Slide No.
1. Introduction 3
2. Representation Of Queue 5
3. Three States Of Queue 6
4. Applications Of Queue 7
5. Types Of Queue 8
6. Circular Queue 9
7. Double – Ended Queue (Deque) 10
8. Operations On Deque 11
9. Application Of Queue 12
10. Priority Queue 13
11. Application Of Priority Queue 14
2

3. Introduction
Queue is an ADT data structure similar to stack, except
that the first item to be inserted is the first one to be
removed.
This mechanism is called First-In-First-Out (FIFO).
Placing an item in a queue is called “insertion or
enqueue”, which is done at the end of the queue called
“rear”.
Removing an item from a queue is called “deletion or
dequeue”, which is done at the other end of the queue
called “front”.
Some of the applications are : printer queue, keystroke
queue, etc.
3

4. C
B C
A B C
A
b a c k
f r o n t
p u s h A
A B
f r o n t b a c k
p u s h B
f r o n t b a c k
p u s h C
f r o n t b a c k
p o p A
f r o n t
b a c k
p o p B
A Queue is a FIFO (First in First
Out) Data Structure. Elements
are inserted in the Rear of the
queue and are removed at the
Front.
4

5. Representation Of Queue
Using An Array
Using A Linked List
5

6. 3 States Of Queue
Queue is Empty :
 Front = Rear
Queue is Full :
 Rear = N
Queue contains element >=1 :
 Front < Rear
 No. Of Element = Rear – Front + 1
6

7. Applications Of Queue
Real Life Applications
 Waiting in line
 Waiting on hold for tech support
Applications Related to computer life
 Round Robin Scheduling
 Job Scheduling
 Key Board Buffer
7

8. Types Of Queue
Circular Queue
Double Ended Queue (Deque)
Priority Queue
8

9. Circular Queue
When a new item is inserted at the rear, the pointer to
rear moves upwards.
Similarly, when an item is deleted from the queue the
front arrow moves downwards.
After a few insert and delete operations the rear might
reach the end of the queue and no more items can be
inserted although the items from the front of the queue
have been deleted and there is space in the queue.
To solve this problem, queues implement wrapping
around. Such queues are called Circular Queues.
Both the front and the rear pointers wrap around to the
beginning of the array
9

10. Double – Ended Queue (Deque)
Items can be inserted and deleted from either ends.
Input Restricted Deque: Elements can be inserted at
only at one end but can be removed from both ends.
Output Restricted Deque: Elements can be inserted at
both ends and can be removed only from one side
10

11. Operations On Deque
Insert element at back
Insert element at front
Remove element at front
Remove element at back
11

12. Applications Of Deque
A-Steal job scheduling algorithm
The A-Steal algorithm implements task scheduling for
several processors(multiprocessor scheduling).
The processor gets the first element from the deque.
When one of the processor completes execution of its own
threads it can steal a thread from another processor.
 It gets the last element from the deque of another
processor and executes it.
Undo-Redo : operations in Software applications.
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13. Priority Queue
A Special form of queue from which items are removed
according to their designated priority and not the order in
which they entered.
Items are removed from the front.
Items are ordered by key value so that the item with the
lowest key (or highest) is always at the front.
Items are inserted in proper position to maintain the
order.
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14. Applications Of Priority Queue
Standby flyers
Auctions
Stock market
Sorting
Huffman Coding
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