Dynamic Queue.

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Presentation Topic
Dynamic Queue.

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Queues
 A Queue is a special kind of list, where
items are inserted at one end (the rear)
And deleted at the other end (the front).
 Accessing the elements of queues follows
a First In First Out (FIFO) order.
 Example
 Like customers standing in a check-out
line in a store, the first customer in is
the first customer served.
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Common Operations on Queues
 getFRONT(Q): Returns the first element on
Queue Q.
 ENQUEUE(x,Q): Inserts element x at the
end of Queue Q.
 DEQUEUE(Q): Deletes the first element of
Q.
 ISEMPTY(Q): Returns true if and only if Q
is an empty queue.
 ISFULL(Q): Returns true if and only if Q is
full.
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Enqueue and Dequeue
 Primary queue operations: Enqueue and
Dequeue
 Enqueue – insert an element at the rear of
the queue.
 Dequeue – remove an element from the
front of the queue.
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Queues Implementations
Static:
Queue is implemented by an array, and size
of queue remains fix
Dynamic:
A queue can be implemented as a linked
list and expand or shrink with each enqueue
or dequeue operation.
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Static Implementation of Queues
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Dynamic Implementation of Queues
Dynamic implementation is done using pointers.
• Front : A pointer to the first element of the
queue.
• Rear : A pointer to the last element of the
queue.
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x y z
Front
Rear
.

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Dynamic Implemenatation
• Enqueue (X)
• Enqueue (Y)
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Q.front
Q.Rear
.
x
Q.front
Q.Rear
x .
y

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Dynamic Implementation
• Dequeue:
• MakeNULL:
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Q.front
Q.Rear
.
y
Q.front
Q.Rear
NULL

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Dynamic implementation of Queue
struct queueNode
{
int num;
queueNode next;
};
queueNode front = NULL;
queueNode rear = NULL;
class dynQueue{
int size;
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public:
dynQueue();
void enqueue();
void dequeue();
bool isEmpty();
void displayQueue();
void makeNull();
};

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Constructor
dynQueue()
{
size=0;
}
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12. z Enqueue( ) Function
Void enqueue(int x)
{
/*Linked list node*/
queueNode *n = new Node();
n->setData(x);
n->Next= NULL;
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if (front == NULL)
{
front = n;
rear = n;
size++;
}
else
{
rear->Next=n;
rear = n;
size++;
}
}

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Dequeue( ) Function
int dequeue()
{
if(front == NULL)
{
cout<<“Queue is Empty“;
}
else
{ queueNode *temp=front;
int x = front->getData();
front = front->getNext();
Delete temp;
return x;
}
}
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getFront() and isEmpty()
int getFront()
{
return front->Data;
}
int isEmpty()
{
return ( front == NULL );
}
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Display( ) Function
void display()
{
if(isEmpty())
cout<<“Queue is empty“;
else
{
for (int i=0; i<counter; i++)
cout<<queue[(front+ i)% maxSize];
}
}
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Use of Queues
Out of the numerous uses of the queues, one of the most
useful is simulation.
A simulation program attempts to model a real-world
phenomenon.
Many popular video games are simulations, e.g., SimCity,
Flight Simulator.
Each object and action in the simulation has a counterpart in
real world.
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Uses of Queues
If the simulation is accurate, the result of the program should
mirror the results of the real-world event.
Thus it is possible to understand what occurs in the real-world
without actually observing its occurrence.
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