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Queue overflow results from trying to add an element onto a full queue and queue underflow happens when trying to remove an element from an empty queue. A bounded queue is a queue limited to a fixed number of items. [1] There are several efficient implementations of FIFO queues.
A double-ended queue is represented as a sextuple (len_front, front, tail_front, len_rear, rear, tail_rear) where front is a linked list which contains the front of the queue of length len_front. Similarly, rear is a linked list which represents the reverse of the rear of the queue, of length len_rear.
The list handle should then be a pointer to the last data node, before the sentinel, if the list is not empty; or to the sentinel itself, if the list is empty. The same trick can be used to simplify the handling of a doubly linked linear list, by turning it into a circular doubly linked list with a single sentinel node.
Examples of FIFO status flags include: full, empty, almost full, and almost empty. A FIFO is empty when the read address register reaches the write address register. A FIFO is full when the write address register reaches the read address register. Read and write addresses are initially both at the first memory location and the FIFO queue is empty.
For queue, because enqueuing and dequeuing occur at opposite ends, peek cannot be implemented in terms of basic operations, and thus is often implemented separately. One case in which peek is not trivial is in an ordered list type (i.e., elements accessible in order) implemented by a self-balancing binary search tree.
A priority queue must at least support the following operations: is_empty: check whether the queue has no elements. insert_with_priority: add an element to the queue with an associated priority. pull_highest_priority_element: remove the element from the queue that has the highest priority, and return it.
The bucket queue is the priority-queue analogue of pigeonhole sort (also called bucket sort), a sorting algorithm that places elements into buckets indexed by their priorities and then concatenates the buckets. Using a bucket queue as the priority queue in a selection sort gives a form of the pigeonhole sort algorithm. [2]
Another example is a similar singly linked type in Java: class List < E > { E value ; List < E > next ; } This indicates that non-empty list of type E contains a data member of type E, and a reference to another List object for the rest of the list (or a null reference to indicate that this is the end of the list).