Queues presentation

ALLAH
the most Gracious, the most
merciful
In the name of

Assignment
Submitted by:
 Toseef Hassan (BSF1600847)
 Muhammad Ishfaq (BSF1604280)
 Muhammad Shahzad (BSF1600951)
 Muhammad Umar (BSF1600824)
Class: BS Information Technology (Eve)-A
Semester: IV Semester
Submitted to:
 Mr. Khalid Mehmood
(Head Of Department)
Information Technology
Division of Science & Technology

Overview:
 Simple Queue
 Circular Queue
 Priority Queue
 Deques
• Input restricted deque
• Output restricted deque

What is a Queue?
 A queue is a linear list which obeys FIFO (First In First
Out) principle to insert & delete values.
 An ordered collection of homogeneous elements.
It’s a non-primitive linear data structure.

Simple Queue
45 20 67 7Q
RearFront

The Queue Operations:
Insertion or Enqueue:
Placing an item in a queue is called “insertion or
enqueue”, which is done at the end of the queue called
“rear” or “tail”.
Deletion or Dequeue:
Removing an item from a queue is called “deletion or
dequeue”, which is done at the other end of the queue
called “front” or “head”.

Algorithm:
If (rear = N-1 )
print (“*Queue is Full*”);
Else
rear = rear + 1; //rear=0
Q[rear] = item
45Q
Rear
0 1 2 3
Where N is the length of array (4 in this
case)
Rear= -1 (First time only)
Front= -1
Item 45

Algorithm:
If (rear = N-1 ) // rear=0
Else
Q[rear] = item
45 32Q
Rear
0 1 2 3
N= 4
Front= -1
Item 32

Algorithm:
Else
Q[rear] = item
45 32 23Q
Rear
0 1 2 3
N= 4
Front= -1
Item 23

Algorithm:
Else
Q[rear] = item
45 32 23 07Q
Rear
0 1 2 3
N= 4
Front= -1
Item 07

NOW
If we again call the insert() function, insertion
is unsuccessful because queue is full.

Algorithm:
Else
rear = rear + 1;
Q[rear] = item
45 32 23 07Q
Rear
0 1 2 3
N= 4
Front= -1
Item 10
*Insertion Unsuccessful*

Algorithm:
If (front =rear) // -1 = 3
print (“Queue is empty”);
Else
Front = front + 1;
item = Q [front];
Return item;
45 32 23 07Q
Rear
0 1 2 3
N= 4
Front= -1
Front

Algorithm:
If (front =rear) // 0 = 3
Else
Front = front + 1;
item = Q [front];
Return item;
32 23 07Q
Rear
0 1 2 3
N= 4
Front= 0
Front

Algorithm:
Else
Front = front + 1;
item = Q [front];
Return item;
23 07Q
Rear
0 1 2 3
N= 4
Front= 1
Front

Algorithm:
Else
Front = front + 1;
item = Q [front];
Return item;
07Q
Rear
0 1 2 3
N= 4
Front= 2
Front

Algorithm:
Else
Front = front + 1;
item = Q [front];
Return item;
Q
Rear
0 1 2 3
N= 4
Front= 3
Front

We have seen that all the values of queue are deleted
one by one, hence it can accommodate four more
values being empty.
But still, we can’t insert new values because;
Rear=3 and “Queue is full” condition invokes.
This is the major fault of simple queue that we can
only insert values once in a queue because there is no
mechanism to bring “rear” back to beginning (0).
Disadvantages of Simple Queue:

Circular Queue:
Circular queues were introduced to overcome the
limitations of simple queue.
As the name indicates a circular queue is not linear in
structure but instead it is circular.
Front and Rear variables display a circular movement
(clock wise) over the queue data structure.
As the Rear or Front variable reaches the end of the
queue, it is send back to beginning of the queue
using the mod function.

A B DCCirc_Q
Front Rear
(a) Initial circular queue
DCCirc_Q
Front Rear
(b) Circular queue after two
deletions
E DCCirc_Q
FrontRear
(c) Circ_Q after insertion of e
E F DCCirc_Q
FrontRear
(d) Circ_Q after insertion of
f
Workingofacircularqueue

Insertion:
 Algorithm:
Insert (front, rear, n, item)
{ int p=rear;
rear= (rear+1)%n; // rear=1
If (front==rear)
{ Print “*Queue is full*”
rear=p;}
Q [rear] = item;
}
45Q
Rear
0 1 2 3
Where N is the length of array (4
in this case)
Rear= 0 (First time only)
Front= 0
Item 45
Front

Insertion:
 Algorithm:
{ int p=rear;
If (front==rear)
rear=p;}
Q [rear] = item;
}
45 32Q
Rear
0 1 2 3
Item 32
Front

Insertion:
 Algorithm:
{ int p=rear;
If (front==rear)
rear=p;}
Q [rear] = item;
}
45 32 23Q
Rear
0 1 2 3
Item 23
Front

Insertion:
 Algorithm:
{ int p=rear; // p=3
If (front==rear)
rear=p;}
Q [rear] = item;
}
45 32 23Q
Rear
0 1 2 3
Item 23
Front

Deletion:
 Algorithm:
Delete (front, rear, n, item)
{ If (front==rear)
Print “*Queue is empty*”;
front = (front+1) % n; // front=1
Item = Q [front];
}
45 32 23Q
Rear
0 1 2 3
Front

Deletion:
 Algorithm:
{ If (front==rear)
Item = Q [front];
}
32 23Q
Rear
0 1 2 3
Front

Deletion:
 Algorithm:
{ If (front==rear)
Item = Q [front];
}
23Q
Rear
0 1 2 3
Front

Deletion:
 Algorithm:
{ If (front==rear)
Item = Q [front];
}
Q
Rear
0 1 2 3
Front

Let’s try Insertion again
{ int p=rear;
If (front==rear)
rear=p;}
Q [rear] = item;
}
70Q
Rear Front
Item 70
0 1 2 3
Rear= 3
Front= 3

{ int p=rear;
If (front==rear)
rear=p;}
Q [rear] = item;
}
70 89Q
Rear Front
Item 89
0 1 2 3
Rear= 0
Front= 3

{ int p=rear;
If (front==rear)
rear=p;}
Q [rear] = item;
}
70 89 27Q
Rear Front
Item 27
0 1 2 3
Rear= 1
Front= 3

{ int p=rear;
If (front==rear)
rear=p;}
Q [rear] = item;
}
70 89 27Q
Rear Front
0 1 2 3
Rear= 2
Front= 3

Priority Queue:
 A priority queue is a queue in which insertion or deletion of
items from any position in the queue are done based on some
property (such as priority of task).

Doctor Example:
Normal Patients Queue
Emergency Patients Queue
1 2 3 4 5
Doctor
SUSPENDED

Deques:
 A deque (double ended queue) is a linear list in which all insertions and
deletions are made at the end of the list. A dequeue is pronounced as
‘deck’ or ‘de queue.’
 A deque is more general than a stack or queue and is a sort of FLIDLO
(First In Last In First Out Last Out).
 A deque has two variants; input restricted queue and output restricted
queue.
 An input restricted dequeue is one where insertions are allowed at one
end only while deletions are allowed at both ends.
 An output restricted dequeue allows insertions at both ends of the queue
but permits deletions only at one end.

Bottom Top
Push
Pop
Stack
Front Rear
Insert
Delete
Queue

Front Rear
Insert
Delete
Dequeue
Delete
Insert

Front Rear
Insert
Delete
Input restricted Dequeue
Delete

Front Rear
Insert
Output restricted Dequeue
Delete
Insert

Queues presentation

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