In this post we will study about “QUEUE” and its application.

                                                             “QUEUE”

• Like stack queue is a linear structure.
• which follows a particular order in which the operations are performed.
• The order is First In First Out (FIFO).
•  Unlike stacks, a queue is open at both its ends.
• One end is always used to insert data (enqueue) and the other is used to remove data (dequeue).

Examples of QUEUE:

• examplee of queue can be a single-lane one-way road where the vehicle enters first exits first.
• queue at the ticket windows and bus-stop.

 

 

Operations on Queue:

There are 4 type of operation performed in queue:

1. Enqueue
2. Dequeue
3. Front
4. Rear. 

 

 

ENQUEUE:

1. The word means add an item to the queue.
2. If the queue is full, then it is said to be an Overflow condition.

Algorithm for enqueue operation:

1. Create a new node
ptr=(qType*)malloc(sizeof(qType))

2. Assign the item to info

set ptr->info = item

3. Adjust ptr
set ptr->next= NULL

4. Check for existing queue

if ( rear==NULL)
{
set rear=ptr
set front=ptr
}

else goto 5.

5. Adjust rear pointer

Set  rear -> next =ptr
Set rear= ptr

6.exit

before enqueue

after enqueue

CODE:

int enqueue(int data)      
   if(isfull())
      return 0;
   
   rear = rear + 1;
   queue[rear] = data;
   
   return 1;
end procedure

 

DEQUEUE:

• Removes an item from the queue.
• The items are popped in the same order in which they are pushed.
• If the queue is empty, then it is said to be an Underflow condition.

 

Algorithm for dequeue operation:

1. Check if  queue is Empty

if (front==NULL)

display “Stack Empty ” and exit else goto 2

2. Set temp=front
3. Adjust fron

front=front->next

4. Display temp->info
5.Free(temp)
6.Exit

before dequeue

after dequeue

code

int dequeue()
 {
   if(isempty())
      return 0;

   int data = queue[front];
   front = front + 1;

   return data;
}

 

FRONT:

• Get the front item from queue.

Code:

int peek() {
   return queue[front];
}

 

REAR:

• Get the last item from queue

code:

bool isempty() {
   if(front < 0 || front > rear) 
      return true;
   else
      return false;
}