PriorityQueue

A queue data structure that maintains a maximum heap property.

Installation

1. File > Add Package Dependency
2. Type https://github.com/Jordan-Gallivan/PriorityQueue in the search window.
3. Select "Add Package"
4. Enjoy!

How to Use

You can use a priority queue instead of a queue when the maximum element in the queue must be accessible in O(1) time without modifying the queue, or O(log n) time by removing the maximum element.

You can create a priority queue with any element type that conforms to the Comparable protocol and that element's comparison method will be used if no comparison function is passed through the trailing closure. If a comparison function is passed as through the trailing closure, the element's existing comparison method will be ignored, and the heap property will be maintained through the use of the passed comparison function.

// create a maximum heap priority queue using the element's comparison function
var intQueue = PriorityQueue([10, 20, 30, 40, 50])
if let intQueueMax = intQueue.peek() {
    print(intQueueMax)
}
// Prints "50"

// create a minimum heap priority queue using a custom comparison function
var minQueue = PriorityQueue([10, 20, 30, 40, 50]) { $1 > $0 }
if let minQueueMin = minQueue.peek() {
    print(minQueueMin)
}
// Prints "10"

You can also create a priority queue with any element type provided a comparison function is passed through the trailing closure.

enum Status {
    case success
    case failure(Int)
}

let collection: [Status] = [.failure(1), .success, .failure(2), .failure(3)]

var enumQueue = PriorityQueue(collection) {
    switch ($0, $1) {
    case let (.failure(aAttempts), .failure(bAttempts)):
        return aAttempts < bAttempts
    case (.success, .success):
        return false
    case (.success, .failure(_)):
        return true
    case (.failure(_), .success):
        return false
    }
}

if let maxElement = enumQueue.poll() {
    print(maxElement)
}
// Prints "success"

if let nextMaxElement = enumQueue.poll() {
    print(nextMaxElement)
}
// Prints "failure(1)"

Accessing Priority Queue Values

Use the isEmpty property to check quickly whether the priority queue has any elements, or use the count property to find the number of elements in the priority queue.

if intQueue.isEmpty {
    print("The Queue is Empty")
} else {
    print("The Queue has \(intQueue.count) elements.")
}
// Prints "The Queue has 5 elements."

Priority Queue Operations

Use the add(_:) method to add an element to the priority queue.

intQueue.add(60)
if let maxElement = intQueue.peek() {
    print(maxElement)
}
// Prints "60"

Use the peek() method to view the maximum element in the priority queue without modifying the queue.

print("The Queue has \(intQueue.count) elements")
if let currentMaxElement = intQueue.peek() {
    print(currentMaxElement)
}
print("The Queue has \(intQueue.count) elements")
// Prints "The Queue has 6 elements."
// Prints "60"
// Prints "The Queue has 6 elements."

Use the poll() method to view and remove the maximum element in the priority queue.

print("The Queue has \(intQueue.count) elements")
if let removedMaxElement = intQueue.poll() {
    print(removedMaxElement)
}
print("The Queue has \(intQueue.count) elements")
// Prints "The Queue has 6 elements."
// Prints "60"
// Prints "The Queue has 5 elements."