Why can’t a Priority Queue wrap around like an ordinary Queue?

Introduction

A queue is an abstract Data type that inserts elements from the Rear end and removes them from the Front end. There are three types of queues: Simple Queue, Priority Queue, and Circular Queue. In this tutorial, we understand why we cannot wrap around a Priority queue and the reasons for it.

Priority Queue

It is a unique queue that is not based on the FIFO principle for Queue operations. What makes it unique? It is the priority of its elements for removing or deQueue. Each element of the priority queue has some priority and they are removed based on that.

The element with the highest priority is removed first from the Queue. When two queue elements have the same priority, they will be removed by the FIFO principle.

The Priority Queue is implemented by using an array, linked list, heap, or binary tree. There are two types of priority queues: the Min priority queue and the max priority queue

Queue

An ordinary queue in a data structure is similar to a real-life queue. It can be implemented by using an array and a linked list. For array queue implementation, you have to define the queue size in advance and this results in a waste of memory. When using an array to implement a simple queue, a few spaces before the rear end remains unused.

Wrap Around: Meaning

To overcome the problem of memory wastage in ordinary queues. A queue is wrapped by forming a cycle between the front end and the rear end. The resulting Queue is known as Circular Queue.

By wrapping, if you insert an element after reaching the maximum size of the Queue, it will be easily inserted.

Before wrapping around the concept, the queue will throw an exception in Java on adding elements after the maximum Queue size. After multiple times of insertions and deletions of Queue elements, you will find that at a certain point Rear end will be below the Front end. This will be because of Wrapping around.

Why Priority Queue cannot be Wrapped Around?

It is possible to use a Priority Queue with wrap-around logic but this will reduce its performance.

The most effective implementation of the priority queue is a binary tree. A binary tree does not have any impact on the wrapping of the front and rear ends.

Priority Queue does not define the different queue operations and it is used for its implementations using an array, linked list, or binary tree.

Wrapping around an ordinary queue results in a ring buffer and Priority Queue can be implemented in various ways.

Priority Queue has various other features than using wrapping around and it defines both queue and stack.

Conclusion

A priority queue is an ordered queue that removes its data with the highest priority. There are several ways to implement it and the most used is the binary tree. The wrapping-around implementation is used with the normal queue.

A normal Queue is unsorted and its elements are removed in the FIFO order. It has two ends: Rear and Front end. It is used in traffic handling, CPU scheduling, or Managing playlists.