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FIFO's opposite is LIFO, last-in-first-out, where the youngest entry or "top of the stack" is processed first. [2] A priority queue is neither FIFO or LIFO but may adopt similar behaviour temporarily or by default. Queueing theory encompasses these methods for processing data structures, as well as interactions between strict-FIFO queues.
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
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 ...
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.
Stack (first in, last out) implemented as a singly linked list, Queue, implemented as a real-time queue, Double-ended queue, implemented as a real-time double-ended queue, (Multi)set of ordered elements and map indexed by ordered keys, implemented as a red–black tree, or more generally by a search tree, Priority queue, implemented as a Brodal ...
Double-ended queues can also be implemented as a purely functional data structure. [3]: 115 Two versions of the implementation exist. The first one, called 'real-time deque, is presented below. It allows the queue to be persistent with operations in O(1) worst-case time, but requires lazy lists with memoization. The second one, with no lazy ...
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 ...
The priority queue can be further improved by not moving the remaining elements of the result set directly back into the local queues after a k_extract-min operation. This saves moving elements back and forth all the time between the result set and the local queues. By removing several elements at once a considerable speedup can be reached.