implementation of Queue, Priority Queue,Circular Queue,Double Ended Queue

In computer science, the queue is a particular kind of abstract data type or the collection in which the entities in the collection are kept in the order and the principal (or only) operations on the collection are the addition of the entities to the rear terminal position, known as enqueue, and removal of the entities from the front terminal position, known as dequeue. This makes the queue a First-In-First-Out (FIFO) data structure. In FIFO data structure, first element added to queue will be the the first one to be removed. This is equivalent to the the requirement that once a new element is added, all elements that were added before have to be removed before the new element can be removed. Often a peek or front operation is also entered, returning the value of the front element without dequeuing it. A queue is an example of a linear data structure, or more abstractly a sequential collection.

Queues provide services in computer science, transport, and the operations research where the various entities such as the data, objects, persons, or events are stored and held to be processed later. In these contexts, the the queue performs the function of a buffer.

Queues are common in computer programs, where they are the implemented as the data structures coupled with the access routines, as the an abstract data structure or in object-oriented languages as the classes. Common implementations are the circular buffers and the linked lists.