Implemented Queue data structure using array andstack techniques

DevKit.podspec

@@ -127,6 +127,11 @@ Collection of commonly used swift code.
     sp.subspec 'Stack' do |ssp|
         ssp.source_files = 'DevKit/DevKit/Classes/Data\ Structures/Stack/*'
     end
+
+    # Queue
+    sp.subspec 'Queue' do |ssp|
+        ssp.source_files = 'DevKit/DevKit/Classes/Data\ Structures/Queue/*'
+    end
   end
 
 end

DevKit/DevKit.xcodeproj/project.pbxproj

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+		8E54C4372142EA73003207CC /* QueueStackTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8E54C4362142EA73003207CC /* QueueStackTests.swift */; };
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 		8E8F4AC22139C87300E2FD66 /* StackTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8E8F4AC12139C87300E2FD66 /* StackTests.swift */; };
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+		8ED0CAB92141CEAE00F05CD6 /* Queueable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8ED0CAB82141CEAE00F05CD6 /* Queueable.swift */; };
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+		8E54C4342142E91A003207CC /* QueueArrayTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = QueueArrayTests.swift; sourceTree = "<group>"; };
+		8E54C4362142EA73003207CC /* QueueStackTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = QueueStackTests.swift; sourceTree = "<group>"; };
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 		8E8F4AC12139C87300E2FD66 /* StackTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StackTests.swift; sourceTree = "<group>"; };
+		8E8F4AC42141B18A00E2FD66 /* QueueArray.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = QueueArray.swift; sourceTree = "<group>"; };
+		8ED0CAB82141CEAE00F05CD6 /* Queueable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Queueable.swift; sourceTree = "<group>"; };
+		8ED0CABA2141D14500F05CD6 /* QueueStack.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = QueueStack.swift; sourceTree = "<group>"; };
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@@ -485,11 +495,21 @@
 			name = Pods;
 			sourceTree = "<group>";
 		};
+		8E54C4332142E906003207CC /* Queue */ = {
+			isa = PBXGroup;
+			children = (
+				8E54C4342142E91A003207CC /* QueueArrayTests.swift */,
+				8E54C4362142EA73003207CC /* QueueStackTests.swift */,
+			);
+			path = Queue;
+			sourceTree = "<group>";
+		};
 		8E8F4AB22138696E00E2FD66 /* Data Structures */ = {
 			isa = PBXGroup;
 			children = (
-				8E8F4ABD2139C6D800E2FD66 /* Stack */,
 				8E8F4AB32138697600E2FD66 /* Linked List */,
+				8E8F4AC32141B17300E2FD66 /* Queue */,
+				8E8F4ABD2139C6D800E2FD66 /* Stack */,
 			);
 			path = "Data Structures";
 			sourceTree = "<group>";
@@ -514,8 +534,9 @@
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 			isa = PBXGroup;
 			children = (
-				8E8F4AC02139C86700E2FD66 /* Stack */,
 				8E8F4ABA2138730100E2FD66 /* Linked List */,
+				8E54C4332142E906003207CC /* Queue */,
+				8E8F4AC02139C86700E2FD66 /* Stack */,
 			);
 			path = "Data Structures";
 			sourceTree = "<group>";
@@ -544,6 +565,16 @@
 			path = Stack;
 			sourceTree = "<group>";
 		};
+		8E8F4AC32141B17300E2FD66 /* Queue */ = {
+			isa = PBXGroup;
+			children = (
+				8ED0CAB82141CEAE00F05CD6 /* Queueable.swift */,
+				8E8F4AC42141B18A00E2FD66 /* QueueArray.swift */,
+				8ED0CABA2141D14500F05CD6 /* QueueStack.swift */,
+			);
+			path = Queue;
+			sourceTree = "<group>";
+		};
 		B4EADB9A0901D69BD2E4AFA6 /* Frameworks */ = {
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@@ -790,6 +821,7 @@
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 				20524724209BB3550067A328 /* StringExtension.swift in Sources */,
 				205246F0209BA8B40067A328 /* UIScreenExtension.swift in Sources */,
+				8ED0CAB92141CEAE00F05CD6 /* Queueable.swift in Sources */,
 				205246F9209BA8B40067A328 /* UICollectionViewExtension.swift in Sources */,
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@@ -800,6 +832,7 @@
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 				205246FD209BA8B40067A328 /* UIColorExtension.swift in Sources */,
 				205246F7209BA8B40067A328 /* UIStackViewExtension.swift in Sources */,
+				8ED0CABB2141D14500F05CD6 /* QueueStack.swift in Sources */,
 				205246FF209BA8B40067A328 /* UISearchBarExtension.swift in Sources */,
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@@ -808,6 +841,7 @@
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 				205246F8209BA8B40067A328 /* UIImageExtension.swift in Sources */,
 				205246D5209BA3200067A328 /* TransitioningNavigationViewOptions.swift in Sources */,
+				8E8F4AC52141B18A00E2FD66 /* QueueArray.swift in Sources */,
 				8E8F4AB52138698B00E2FD66 /* LinkedListNode.swift in Sources */,
 				205246D3209B9E8F0067A328 /* TransitioningNavigationView.swift in Sources */,
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@@ -823,6 +857,8 @@
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 				8E8F4AC22139C87300E2FD66 /* StackTests.swift in Sources */,
+				8E54C4352142E91A003207CC /* QueueArrayTests.swift in Sources */,
+				8E54C4372142EA73003207CC /* QueueStackTests.swift in Sources */,
 				8E8F4ABC2138731500E2FD66 /* LinkedListTests.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;

DevKit/DevKit/Classes/Data Structures/Queue/QueueArray.swift

@@ -0,0 +1,70 @@
+//
+//  QueueArray.swift
+//  DevKit
+//
+//  Created by Thibault Klein on 9/6/18.
+//  Copyright © 2018 Jonathan Samudio. All rights reserved.
+//
+
+import Foundation
+
+/// QueueArray.
+/// A queue is a collection of elements following a First-In-First-Out (FIFO) order.
+/// This implementation uses an array to store the elements.
+///
+/// - Note:
+/// Use a Queue if you need a sequence ordered as FIFO.
+///
+/// - The advantage of using an array is its simplicity and relative low memory impact.
+/// - The disadvantage is a O(n) complexity every time an element gets dequeued.
+/// Very large queues will have a bad performance using QueueArray.
+open class QueueArray<T>: Queueable {
+    public typealias Element = T
+
+    // MARK: - Public Properties
+
+    /// `true` if the stack is empty. `false` if not.
+    public var isEmpty: Bool {
+        return peek() == nil
+    }
+
+    // MARK: - Private Properties
+
+    private var storage: [Element] = []
+
+    // MARK: - Initialization
+
+    public init() { }
+
+    // MARK: - Public Functions
+    // MARK: General Functions
+
+    /// Returns the value at the end of the queue.
+    ///
+    /// - Complexity: O(1)
+    /// - Returns: The value at the end of the queue.
+    public func peek() -> Element? {
+        return storage.last
+    }
+
+    // MARK: Adding Functions
+
+    /// Enqueues an element at the beginning of the queue.
+    ///
+    /// - Complexity: O(1)
+    /// - Parameter value: The value to enqueue.
+    public func enqueue(_ value: Element) {
+        storage.append(value)
+    }
+
+    // MARK: Removing Functions
+
+    /// Dequeues the element at the end of the queue.
+    ///
+    /// - Complexity: O(n)
+    /// - Returns: The dequeued element.
+    public func dequeue() -> Element? {
+        return isEmpty ? nil : storage.removeFirst()
+    }
+
+}

DevKit/DevKit/Classes/Data Structures/Queue/QueueStack.swift

@@ -0,0 +1,75 @@
+//
+//  QueueStack.swift
+//  DevKit
+//
+//  Created by Thibault Klein on 9/6/18.
+//  Copyright © 2018 Jonathan Samudio. All rights reserved.
+//
+
+import Foundation
+
+/// QueueStack.
+/// A queue is a collection of elements following a First-In-First-Out (FIFO) order.
+/// This implementation uses two stacks to store the elements.
+///
+/// - Note:
+/// Use a Queue if you need a sequence ordered as FIFO.
+///
+/// - The advantage of using two stack is constant complexity when enqueueing and dequeueing.
+/// QueueStack has better performance when working with large queues than QueueArray.
+open class QueueStack<T>: Queueable {
+    public typealias Element = T
+
+    // MARK: - Public Properties
+
+    /// `true` if the stack is empty. `false` if not.
+    public var isEmpty: Bool {
+        return leftStack.isEmpty && rightStack.isEmpty
+    }
+
+    // MARK: - Private Properties
+
+    private var leftStack: [T] = []
+    private var rightStack: [T] = []
+
+    // MARK: - Initialization
+
+    public init() { }
+
+    // MARK: - Public Functions
+    // MARK: General Functions
+
+    /// Returns the value at the end of the queue.
+    ///
+    /// - Complexity: O(1)
+    /// - Returns: The value at the end of the queue.
+    public func peek() -> T? {
+        return !leftStack.isEmpty ? leftStack.last : rightStack.first
+    }
+
+    // MARK: Adding Functions
+
+    /// Enqueues an element at the beginning of the queue.
+    ///
+    /// - Complexity: O(1)
+    /// - Parameter value: The value to enqueue.
+    public func enqueue(_ value: T) {
+        rightStack.append(value)
+    }
+
+    // MARK: Removing Functions
+
+    /// Dequeues the element at the end of the queue.
+    ///
+    /// - Complexity: O(1)
+    /// - Returns: The dequeued element.
+    public func dequeue() -> T? {
+        if leftStack.isEmpty {
+            leftStack = rightStack.reversed()
+            rightStack.removeAll()
+        }
+
+        return leftStack.popLast()
+    }
+
+}

DevKit/DevKit/Classes/Data Structures/Queue/Queueable.swift

@@ -0,0 +1,23 @@
+//
+//  Queueable.swift
+//  DevKit
+//
+//  Created by Thibault Klein on 9/6/18.
+//  Copyright © 2018 Jonathan Samudio. All rights reserved.
+//
+
+import Foundation
+
+/// Defines how a queue can be implemented.
+/// There are different techniques you can use to create a queue (array, doubly linked list, ring buffer, double stack...)
+/// that can confirm to this protocol.
+public protocol Queueable {
+    associatedtype Element
+
+    var isEmpty: Bool { get }
+
+    func peek() -> Element?
+    func enqueue(_ value: Element)
+    func dequeue() -> Element?
+
+}

DevKit/DevKitTests/Classes/Data Structures/Queue/QueueArrayTests.swift

@@ -0,0 +1,69 @@
+//
+//  QueueArrayTests.swift
+//  DevKitTests
+//
+//  Created by Thibault Klein on 9/7/18.
+//  Copyright © 2018 Jonathan Samudio. All rights reserved.
+//
+
+import DevKit
+import XCTest
+
+class QueueArrayTests: XCTestCase {
+
+    func test_queueArray_IsEmpty_EmptyList() {
+        // Given
+        let queue = QueueArray<Int>()
+        // Then
+        XCTAssertTrue(queue.isEmpty)
+    }
+
+    func test_queueArray_IsEmpty_NonEmptyList() {
+        // Given
+        let queue = QueueArray<Int>()
+        // When
+        queue.enqueue(1)
+        // Then
+        XCTAssertFalse(queue.isEmpty)
+    }
+
+    func test_queueArray_Peek_EmptyList() {
+        // Given
+        let queue = QueueArray<Int>()
+        // Then
+        XCTAssertNil(queue.peek())
+    }
+
+    func test_queueArray_Enqueue() {
+        // Given
+        let queue = QueueArray<Int>()
+        XCTAssertNil(queue.peek())
+        // When
+        queue.enqueue(1)
+        // Then
+        XCTAssertEqual(queue.peek()!, 1)
+    }
+
+    func test_queueArray_Dequeue_EmptyList() {
+        // Given
+        let queue = QueueArray<Int>()
+        XCTAssertNil(queue.peek())
+        // When
+        queue.enqueue(1)
+        // Then
+        XCTAssertEqual(queue.dequeue()!, 1)
+    }
+
+    func test_queueArray_Dequeue() {
+        // Given
+        let queue = QueueArray<Int>()
+        XCTAssertNil(queue.peek())
+        // When
+        queue.enqueue(1)
+        queue.enqueue(2)
+        queue.enqueue(3)
+        // Then
+        XCTAssertEqual(queue.dequeue()!, 1)
+    }
+
+}