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Queue

Subtopics:

Simple Queue

Circular Queue

Project Made by:

Mehul BhanderiKishan Jasani

Vinesh KumbhaniNilay Bharti

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1. Introduction ____________________________________________________3

2. Operations _____________________________________________________6

3.Illustration of Simple Queue _______________________________________7

4.Algorithm for inserting data in Simple Queue __________________________8

5.Algorithm for deleting data from Simple Queue ________________________96.Drawback of Simple Queue________________________________________10

7.Circular Queue__________________________________________________12

8. Illustration of Circular Queue______________________________________13

9.Algorithm for inserting data in Circular Queue_________________________19

10. Algorithm for deleting data from Cicular Queue ______________________20

11. Summary and Conclusion________________________________________21

12. Sources______________________________________________________22

INDEX

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1. Introduction

QueueA queue is a particular kind of collection in which the entitiesin the collection are kept in order and the principal (or only)operations on the collection are the addition of entities tothe rear terminal position and removal of entities from the

front terminal position. This makes the queue a First-In-First-Out (FIFO) data structure. In a FIFO data structure,the first element added to the queue will be the first one tobe removed. This is equivalent to the requirement thatonce an element is added, all elements that were added

before have to be removed before the new element can beinvoked. A queue is an example of a linear data structure.

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Queues provide services in computer science,transport, and operations research where variousentities such as data, objects, persons, or events arestored and held to be processed later. In thesecontexts, the queue performs the function of a buffer.

Queues are common in computer programs, wherethey are implemented as data structures coupledwith access routines, as an abstract data structure orin object-oriented languages as classes. Common

implementations are circular buffers and linked lists.

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The defining attribute of a queue data structure is

the fact that allows access to only the front andback of the structure. Furthermore, elements canonly be removed from the front and can only beadded to the back. In this way, an appropriatemetaphor often used to represent queues is the

idea of a checkout line. Other examples of queuesare people traveling up an escalator, machineparts on an assembly line, or cars in line at apetrol station. The recurring theme is clear:

queues are essentially the same as a queue youwould get in a shop waiting to pay.

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2. Operations

In queue, data elements are added at one end, calledthe rear and removed from another end, called the fron tof the list.

Two basic operations are associated with queue:

1. Insert operation is used to insert an element into a

queue.

2. Delete operation is used to delete an element from a

queue.

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3. Consider the following queue (simple queue).

Rear = 4 and Front = 1 and N = 7

10 50 30 40

(1) Insert 20. Now Rear = 5 and Front = 1

1 2 3 4 5 6 7

10 50 30 40 201 2 3 4 5 6 7

(2) Delete Front Element. Now Rear = 5 and Front = 2

50 30 40 201 2 3 4 5 6 7

(3) Delete Front Element. Now Rear = 5 and Front = 3

30 40 201 2 3 4 5 6 7

(4) Insert 60. Now Rear = 6 and Front = 3

30 40 20 601 2 3 4 5 6 7

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4. Algorithm for inserting data inSimple Queue:Insert ( ):Here QUEUE is an array with N locations. FRONT andREAR points to the front and rear ofthe QUEUE. ITEM is the value to be inserted.1. If (REAR == N) Then [Check for overflow]2. Print: Overflow

3. Else4. If (FRONT and REAR == 0) Then [Check if QUEUE isempty](a) Set FRONT = 1(b) Set REAR = 15. Else

6. Set REAR = REAR + 1 [Increment REAR by 1][End of Step 4 If]7. QUEUE[REAR] = ITEM8. Print: ITEM inserted[End of Step 1 If]9. Exit

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5. Algorithm for deleting data:Delete ( ):

Here QUEUE is an array with N locations. FRONT and REARpoints to the front and rear ofthe QUEUE.1. If (FRONT == 0) Then [Check for underflow]2. Print: Underflow3. Else

4. ITEM = QUEUE[FRONT]5. If (FRONT == REAR) Then [Check if only one element is left](a) Set FRONT = 0(b) Set REAR = 06. Else7. Set FRONT = FRONT + 1 [Increment FRONT by 1][End of Step 5 If]8. Print: ITEM deleted[End of Step 1 If]9. Exit

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6. Drawback of Simple Queue

Problem: RightwardDrifting:

After a sequence of additions and removals, items will

drift towards the end of the array

Even though, there are empty spaces in front of the

queue array, insert operation cannot be performed

on the queue, since back= size - 1.

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Rightward Drifting Solutions

To optimize space and to solve rightward drifting:

Shift array elements after each deletion.

However, shifting is not effective and dominates

the cost of the implementation.

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7. Circular Queue:Using a circular array makes it easier: When front

or back reach theend of the array, wrap them around to the

beginning of the array.

Let's see inserting and

Deleting of data.

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8. Example: Consider the following circular queuewith N=5

.

Initially, Rear = 0, Front =

0.

2. Insert 10, Rear = 1, Front = 1.Rear

Front

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3. Insert 50, Rear = 2, Front = 1.

RearFront

4. Insert 20, Rear = 3, Front = 0.

Rear

Front

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5. Insert 70, Rear = 4, Front = 1.

6. Delete front, Rear = 4, Front = 2.

Rear

Rear

Front

Front

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7. Insert 100, Rear = 5, Front = 2.

8. Insert 40, Rear = 1, Front = 2.

Front

Rear

Front

Rear

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9. Insert 140, Rear = 1, Front = 2. As Front = Rear + 1, so Queue overflow.

Rear Front

10. Delete front, Rear = 1, Front = 3.

Rear

Front

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11. Delete front, Rear = 1, Front = 4.

12. Delete front, Rear = 1, Front = 5.

Rear

Rear

Front

Front

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9. Algorithm to insert data in Circular Queue:Here QUEUE is an array with N locations. FRONT and REAR points to the front and rear

elements of the QUEUE. ITEM is the value to be inserted.1. If (FRONT == 1 and REAR == N) or (FRONT == REAR + 1) Then

2. Print: Overflow

3. Else

4. If (REAR == 0) Then [Check if QUEUE is empty]

(a) Set FRONT = 1

(b) Set REAR = 1

5. Else If (REAR == N) Then [If REAR reaches end if QUEUE]

6. Set REAR = 1

7. Else

8. Set REAR = REAR + 1 [Increment REAR by 1]

[End of Step 4 If]9. Set QUEUE[REAR] = ITEM

10. Print: ITEM inserted

[End of Step 1 If]

11. Exit

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10. Algorithm to delete data from CircularQueue:Here QUEUE is an array with N locations. FRONT and

REAR points to the front and rearelements of the QUEUE.1. If (FRONT == 0) Then [Check for Underflow]2. Print: Underflow3. Else4. ITEM = QUEUE[FRONT]

5. If (FRONT == REAR) Then [If only element is left](a) Set FRONT = 0(b) Set REAR = 06. Else If (FRONT == N) Then [If FRONT reaches end ifQUEUE]7. Set FRONT = 1

8. Else9. Set FRONT = FRONT + 1 [Increment FRONT by 1][End of Step 5 If]10. Print: ITEM deleted[End of Step 1 If]11. Exit

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11. Summary and Conclusion Queue can be implemented using linear array and

circulararray. Structure of queue is linear, items that manage thearray are front and back. Insertion happens at back, while deletion happens at

front. Drawback of simple queue is that it will lead torightward drifting problem after sequence of deletionand insertion is performed on the queue. Circular Queue can be used in order to solve the

problem, whereby after front or back reach the end ofthe array, it will wrap around to the beginning of thearray.

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12 . Sources:

http://www.wiziq.com/tutorial/191784-Linear-Queue-and-Circular-Queue

https://www.princeton.edu/~achaney/tmve/wiki100k/docs/

Queue_(data_structure).html

http://www.w3professors.com/Pages/Courses/Data-Structure/Algorithms/Data-Structure-Algorithm.html

http://ocw.utm.my/file.php/31/Module/ocwQueueDec2011.pdf

http://mithun039.weebly.com/uploads/3/5/3/6/3536408/queue.ppt

http://www.wiziq.com/tutorial/191784-Linear-Queue-andhttps://www.princeton.edu/~achaney/tmve/wiki100k/docs/http://www.w3professors.com/Pages/Courses/Data-Structurehttp://www.w3professors.com/Pages/Courses/Data-Structurehttp://www.w3professors.com/Pages/Courses/Data-Structurehttp://www.w3professors.com/Pages/Courses/Data-Structurehttp://www.w3professors.com/Pages/Courses/Data-Structurehttps://www.princeton.edu/~achaney/tmve/wiki100k/docs/https://www.princeton.edu/~achaney/tmve/wiki100k/docs/http://www.wiziq.com/tutorial/191784-Linear-Queue-andhttp://www.wiziq.com/tutorial/191784-Linear-Queue-andhttp://www.wiziq.com/tutorial/191784-Linear-Queue-andhttp://www.wiziq.com/tutorial/191784-Linear-Queue-andhttp://www.wiziq.com/tutorial/191784-Linear-Queue-andhttp://www.wiziq.com/tutorial/191784-Linear-Queue-andhttp://www.wiziq.com/tutorial/191784-Linear-Queue-andhttp://www.wiziq.com/tutorial/191784-Linear-Queue-and