A priority queue is a queue in which we insert an element at the back (enqueue) and remove an element from the front (dequeue). In addition, every element has a priority associated with it. The element with the highest priority shall be dequeued first. The Priority queue can be implemented with array or heap.

There are two ways to implement with array. The first is to implement as an ordered array. All element are ordered when insert. To dequeue, remove the last element which has the highest priority. The second way is to allow new element to enter in an arbitrary order. To dequeue, find the highest priority element by checking all elements and remove it. This post is using the first approach. For the second approach, check out implement priority queue with unordered array.

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Enqueue

To enqueue an element in priority queue is the same as adding an element in a sorted array. If it is a descending priority (ie the bigger the key, the higher the priority), you can put the highest key at the end. If it is a ascending priority (ie the lower the key, the higher the priority), you put the lowest key at the end. In this implementation, we are applying descending priority.

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Doodle

priority queue ordered array


Dequeue

The dequeue operation is to remove the highest priority element from the array. Since the array is already sorted, we can just remove the last element.

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Peek

Peek is to return the value of the highest priority element. The same as dequeue, we simply return the value of the element at highest index.

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Print

Print is to print all elements in the array, starting from the index 0 to highest index. A for loop is used to iterate through each element.

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