In the former, each parent node is equal to or less than the values of its child nodes. This can be done with either a min heap or a max heap. This is because they’re a tree structure with the heap property. This implementation is preferred a lot of the time, as it often gives better performance. The operations used with this type of queue follow the same syntax, so for brevity’s sake, they won’t be included here. The element is inserted by assigning the new node as the next node of the current node. If the priority of the inserted element is lower than the head node, then we must traverse the list and compare it with each element to find the correct position. Therefore, they must be inserted more thoughtfully. This is because we can simply update the front pointer to the next node to remove an element, but linked lists don’t have random access to elements. The “delete” method is relatively simple here, but the “insert” method is more complicated than before. We must declare the “Node” class to represent each element. Most of the logic here is the same, but we define the methods differently. While current.next is not None and <= priority: This is similar to an array but uses pointers and nodes, and can be dynamically resized. © Linked list-based priority queueĪnother way to implement a priority queue is by using a linked list. A priority queue is implemented using an array. The size and highest-priority element are printed, then each task is printed as it’s processed and deleted. We finish by creating a queue with 3 elements, or “tasks”, with their priorities. After that, the “isEmpty” and “size” methods are defined. Similarly, the “peek” method iterates over the list and returns the item with the highest priority. The elements are then reordered according to priority, and the highest-priority element is removed via the “pop” method. We then assign the highest priority to the first element, but then compare this with the other elements. The “delete” method is defined after this, which removes the element with the highest priority. Then, we define the “insert” method, which takes the “item” argument and the “priority” argument, which is used to assign a priority value to the element. Print("Processing:", task) Explanation of codeįirst, we declare the “PriorityQueue” class, and the “_init_” method, which initializes the queue. The following code in Python shows an example of this. One of the simplest ways to use a priority queue is with an array. We’re going to cover each of these briefly. Generally, you can use an array, a linked list, or a binary heap. Similar to other queues, there are many ways to implement a priority queue. We can also use size and isEmpty with priority queues, to check the queue size and status. Since a priority queue doesn’t obey the FIFO principle, elements are inserted or removed depending on their priority. Priority queues use many of the same operations as other queues – these include insertion, deletion, and peek (retrieves the highest-priority element). Generally, the priority is predefined before execution. When implementing a priority queue, the elements are accessed in order of their priority, with the highest-priority elements being dealt with first. As such, a priority queue is a much more appropriate structure to use here. In these cases, there is still a queue present, but the order in which people leave the queue depends on their priority. Think about the emergency room at a hospital, loyalty customers of a business, or prioritized baggage at an airport. However, this type of queue isn’t applicable to some situations. This logic is found in many real-life queues, such as people queuing for a burger stand or theme park ride, or waiting in a call list for a call center. This means that the first element to be inserted will be the first to be removed. Typical queues, such as linear or circular queues, follow the First-In-First-Out (FIFO) principle. In this article, we’re going to look at how priority queues work, the different ways we can implement them, and best practices. This kind of queue departs from the typical conventions of an ordinary queue but this behavior is desirable in certain scenarios. One of the most fundamental types is the priority queue. There are many kinds of queue structures in programming, each with its own advantages and applications.
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