A queue is a first-in, first-out (FIFO) linear data structure where elements are inserted at the rear of the queue and deleted from the front, with Agner Krarup Erlang applying queueing theory principles to telecommunications; common queue types include deque, circular queue, and priority queue, with priority queues processing elements based on assigned priority levels rather than insertion order. Real-world applications of queues include lines at stores, people on escalators, traffic light patterns, and resource sharing in computer systems like CPU and disk scheduling.

1. Queue is an abstract data structure that follows the FIFO
(First In First Out) principle where an element that is added
first will be deleted first. Also, there are linear data structures
as the elements are linearly arranged.
QUEUE

2. Agner Krarup Erlang (1878-1929) the Danish
telecommunication engineer started applying principles of
queuing theory in the area of telecommunications.

3. QUEUE--

4. Operations on Queue---
 1.Insertion :
Placing an item in a queue is called “insertion or “enqueue”, which is done at the end
of the queue called “rear”.
 2.Deletion :
Removing an item from a queue is called “deletion or “dequeue” , which is done at the
other end of the queue called “front”

6. Types of Queues--
1. Deque
2. Circular Queue
3. Priority Queue

7. DEQUES--
 1.Deque stands for double ended queue.
 2.Elements can be inserted or deleted at either end.
 3. Also known as head-tail linked list.

8. TYPE OF DEQUEUE--
 Input restricted dequeue
Element can be inserted only at one end.
Element can be removed by both end.
 Output restricted dequeuer
Element can be inserted at both end.
Element can be removed by one end.

9. CIRCULAR QUEUES---
 • 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”

10. PRIORITY QUEUE---
 1.It is collection of elements where elements are stored according to the their
priority levels.
 2.Inserting and removing of elements from queue is decided by the priority of the
elements.
 3. An element of the higher priority is processed first.
 4.Two element of same priority are processed on first-come-first-served basis.

11. Example: Suppose you have a few assignment
from different subjects.Which assignment will you
want to do first?
Subject Due date Priority
DLD 6 OCT 2020 1
OR 12 OCT 2020 3
DSN 10 OCT 2020 2
DSA 13 OCT 2020 4

12. APPLICATIONS--
**Real world applications**
 Cashier line in any store.
 Waiting on hold for tech support.
 people on an escalator.
 Checkout at any book store
 Traffic light functioning is the best example for circular queues. The colors in the
traffic light follow a circular pattern.
 In page replacement algorithms, a circular list of pages is maintained and when a page
needs to be replaced, the page in the front of the queue will be chosen.

13. Real world applications---
Please play this Video

14. Real world applications---

15. Applications related to computer science:
 1.When data is transferred asynchronously between two processes.
eg. IO Buffers.
 2.When a resource is shared among multiple consumers. Examples include CPU
scheduling, Disk Scheduling.
 3.In recognizing palindrome.
 4.In shared resources management.
 5.Keyboard buffer.
 6.Round robin scheduling.
 7.Job scheduling. 8.Simulation

16. DHEERENDRA
KUMAR
19BEE10025