Queue ADT

Introduction:

• Like stacks, queues are also lists.
• In queue insertion is done at one end(Rear) and deletion is done at the other end(Front).
• The removal of elements from a queue is possible in the same order in which the insertion of elements is made in to the queue. 
• Since it is always the first  item to be put in to the queue that is the first item to be removed a queue is a First In First Out(FIFO) data structure

                                           A   B   C    D   E   F
                                            |                            |
                                        Front                      Rear

• Queues are used in network programming,operating systems and other situations in which many different processes must share resources such as CPU time.

Basic Queue Operation: 

• Elements can only be added to the rear of the queue and removed from the front of the queue. 
• Insertion of an element in to a queue is known as enqueue and removing an element from the queue is known as dequeue. 

      1. Insertion operation in a queue(enqueue)  

• Inserts an element at the end of the queue.
• When a new element is added to the queue the rear pointer is incremented

      2. Deletion operation in a queue(dequeue)

• removes and returns the element at the front of the queue. 
• When a dequeue operation is performed the element pointed by the front pointer is removed and the front pointer is incremented.

Applications of Queue:

1. Waiting Lists
2. Access to shared resources (eg,Printer)
3. Multiprogramming 
4. Round Robin Scheduling