A queue is an ordered list in which insertions are done at one end (rear) and deletions are done at other end (front). The first element to be inserted is the first one to be deleted. Hence, it is called First in First out (FIFO) or Last in Last out (LILO) list.
Similar to Stacks, special names are given to the two changes that can be made to a queue. When an element is inserted in a queue, the concept is called EnQueue, and when an element is removed from the queue, the concept is called DeQueue.
DeQueueing an empty queue is called underflow and EnQueuing an element in a full queue is called overflow. Generally, we treat them as exceptions. As an example, consider the snapshot ofthe queue.
- EnQueue(int data): Inserts an element at the end of the queue.
- DeQueue(): Removes and returns the element at the front of the queue.
- Front(): Returns the element at the front without removing it.
- QueueSize(): Returns the number of elements stored in the queue.
- IsEmptyQueueQ: Indicates whether no elements are stored in the queue or not.
- Operating systems schedule jobs (with equal priority) in the order of arrival (e.g., a print queue).
- Simulation of real-world queues such as lines at a ticket counter or any other first-
- come first-served scenario requires a queue.
- Multiprogramming.
- Asynchronous data transfer (file IO, pipes, sockets).
- Waiting times of customers at call center.
- Determining number of cashiers to have at a supermarket.
- Auxiliary data structure for algorithms
- Component of other data structures