What is Queue ? Algorithms to insert and delete in queue.

What is Queue ?

Queue is ordered collection of homogeneous data elements in which insertion and deletion operation take place at two end . insertion allowed from starting of queue called FRONT point and deletion allowed from REAR end only

• insertion operation is called ENQUEUE
• deletion operation is called DEQUEUE 

Block Diagram of Queue

Conditions in Queue

• FRONT < 0 ( Queue is Empty )
• REAR = Size of Queue ( Queue is Full )
• FRONT < REAR ( Queue contains at least one element )
• No of elements in queue is : ( REAR - FRONT ) + 1

Restriction in Queue

we can not insert element directly at middle index (position) in Queue and vice verse for deletion. insertion operation possible at REAR end only and deletion operation at FRONT end, to insert we increment REAR and to delete we increment FRONT.

Algorithm for ENQUEUE (insert element in Queue)

Input : An element say ITEM that has to be inserted.
Output : ITEM is at the REAR of the Queue.
Data structure : Que is an array representation of queue structure with two pointer FRONT and REAR.

Steps: 1.  If ( REAR = size ) then //Queue is full 2.        print "Queue is full" 3.        Exit 4.  Else 5.        If ( FRONT = 0 ) and ( REAR = 0 ) then //Queue is empty 6.               FRONT = 1 7.        End if 8.        REAR = REAR + 1 // increment REAR 9.        Que[ REAR ] = ITEM 10. End if 11. Stop

Algorithm for DEQUEUE (delete element from Queue)

Input : A que with elements. FRONT and REAR are two pointer of queue .
Output : The deleted element is stored in ITEM.
Data structure : Que is an array representation of queue structure..

Steps: 1.  If ( FRONT = 0 ) then 2.        print "Queue is empty" 3.        Exit 4.  Else 5.        ITEM = Que [ FRONT ] 6.        If  ( FRONT  =  REAR ) 7.               REAR = 0 8.               FRONT = 0 9.        Else 10.             FRONT  =  FRONT + 1 11.      End if 12. End if  13. Stop

What Next !!

Implement program using this Algorithms, if any query or suggestion then comment it.