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In computer science, a double-ended priority queue (DEPQ) [1] or double-ended heap [2] is a data structure similar to a priority queue or heap, but allows for efficient removal of both the maximum and minimum, according to some ordering on the keys (items) stored in the structure. Every element in a DEPQ has a priority or value.
A queue may be implemented as circular buffers and linked lists, or by using both the stack pointer and the base pointer. Queues provide services in computer science, transport, and operations research where various entities such as data, objects, persons, or events are stored and held to be processed later. In these contexts, the queue ...
Priority queue (such as a heap) Double-ended queue (deque) Double-ended priority queue (DEPQ) Single-ended types, such as stack, generally only admit a single peek, at the end that is modified. Double-ended types, such as deques, admit two peeks, one at each end. Names for peek vary. "Peek" or "top" are common for stacks, while for queues ...
While priority queues are often implemented using heaps, they are conceptually distinct from heaps. A priority queue is an abstract data type like a list or a map; just as a list can be implemented with a linked list or with an array, a priority queue can be implemented with a heap or another method such as an ordered array.
A double-ended queue can be used to store the browsing history: new websites are added to the end of the queue, while the oldest entries will be deleted when the history is too large. When a user asks to clear the browsing history for the past hour, the most recently added entries are removed.
This is the motivation for the second readers–writers problem, in which the constraint is added that no writer, once added to the queue, shall be kept waiting longer than absolutely necessary. This is also called writers-preference. A solution to the writers-preference scenario is: [2]
Similarly to a stack of plates, adding or removing is only practical at the top. Simple representation of a stack runtime with push and pop operations. In computer science, a stack is an abstract data type that serves as a collection of elements with two main operations: Push, which adds an element to the collection, and
Both stacks and queues are often implemented using linked lists, and simply restrict the type of operations which are supported. The skip list is a linked list augmented with layers of pointers for quickly jumping over large numbers of elements, and then descending to the next layer. This process continues down to the bottom layer, which is the ...