# Different Queue Algorithms and Techniques

19 March

Queue algorithms and techniques are fundamental in computer science and are used in a wide variety of applications, such as job scheduling, network packet processing, and operating systems. Queues are data structures that store a collection of items and process them in a specific order. Different types of queue algorithms and techniques are designed to serve specific purposes like java program to add two numbers, and they differ in their processing order and the rules they follow for adding and removing items.

First-In-First-Out (FIFO)

First-In-First-Out (FIFO) is a queue algorithm that processes items in the order they were added to the queue. The first item that was added to the queue is the first one to be processed, and so on. This means that the queue operates on a "first come, first served" basis.

In a FIFO queue, items are added to the end of the queue and removed from the front. This is commonly referred to as the "enqueue" and "dequeue" operations, respectively. The enqueue operation adds an item to the back of the queue, while the dequeue operation removes the item from the front of the queue.

FIFO queues are commonly used in a variety of applications, such as job scheduling, process scheduling, and network packet processing. They are also used in computer science as a data structure to implement other algorithms, such as breadth-first search, multilevel feedback queue scheduling and level-order traversal in trees.

Last-In-First-Out (LIFO)

Last-In-First-Out (LIFO) is a queue algorithm that processes items in the opposite order they were added to the queue. The last item that was added to the queue is the first one to be processed, and so on. This means that the queue operates on a "last come, first served" basis.

In a LIFO queue, items are added to the front of the queue and removed from the front as well. This is commonly referred to as the "push" and "pop" operations, respectively. The push operation adds an item to the front of the queue, while the pop operation removes the item from the front of the queue.

LIFO queues are commonly used in a variety of applications, such as function call stack in programming languages, where the most recent function call is executed first, and in undo-redo operations, where the most recent change is undone or redone first.

Priority Queue

A priority queue is a queue algorithm that processes items based on their priority level. Items with higher priority are processed before items with lower priority. Priority levels can be set either by the user or automatically based on specific criteria.

In a priority queue, items are added with a priority level, and the algorithm ensures that items with higher priority are processed first, regardless of the order in which they were added. Items with equal priority are processed in the order in which they were added.

Priority queues can be implemented using various data structures such as binary heaps, Fibonacci heaps, or balanced search trees. A binary heap is a common implementation that uses a binary tree where each node is smaller than its children. The root node of the binary heap contains the highest-priority item in multilevel feedback queue scheduling.

A priority queue is a queue algorithm that processes items based on their priority level. Items with higher priority are processed before items with lower priority. Priority levels can be set either by the user or automatically based on specific criteria.

In a priority queue, items are added with a priority level, and the algorithm ensures that items with higher priority are processed first, regardless of the order in which they were added. Items with equal priority are processed in the order in which they were added.

Priority queues can be implemented using various data structures such as binary heaps, Fibonacci heaps, or balanced search trees. A binary heap is a common implementation that uses a binary tree where each node is smaller than its children. The root node of the binary heap contains the highest-priority item.

Priority queues are used in many applications, such as job scheduling, event-driven simulations, and network packet processing. They are also used as a core data structure for various algorithms, such as Dijkstra's algorithm for finding the shortest path in a graph, and Huffman coding for data compression.

Round Robin

Round Robin is a queue algorithm that processes items in a circular manner, where each item is assigned a time slice or quantum, and then the algorithm moves on to the next item. Each item is processed for a certain amount of time, and then the algorithm moves on to the next item, regardless of whether the previous item has finished processing or not.

In a Round Robin queue, items are added to the end of the queue, and the algorithm processes them in the order they were added. Each item is assigned a fixed time slice, and the algorithm switches to the next item after the time slice has elapsed. If an item is not finished processing when its time slice ends, it is moved to the back of the queue and processed again when its turn comes up.

Round Robin is commonly used in time-sharing systems, such as operating systems, where multiple processes share the CPU. Each process is assigned a fixed time slice, and the CPU switches between the processes in a circular manner, giving each process a chance to execute. Round Robin can ensure fairness among the processes, as each process is given a fixed amount of CPU time.

Double-ended Queue (Deque)

A double-ended queue (Deque) is a queue algorithm that allows insertion and removal of items from both ends of the queue. Items can be added to or removed from the front or back of the queue.

In a deque, items are stored in a linear data structure, such as an array or a linked list. The front and back of the deque are two pointers that point to the first and last items in the queue, respectively.

Deques are commonly used in applications that require frequent insertion and removal of items from both ends of the queue, such as implementing a sliding window protocol or a breadth-first search algorithm.

Double-ended queues can be implemented using various data structures such as arrays, linked lists, or circular buffers. Linked lists are a common implementation, as they allow dynamic resizing of the deque.

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