playground 一个 queueArray 示例

public struct QueueArray<T>: Queue {
  
  private var array: [T] = []
  public init() {}

  public var isEmpty: Bool {
    array.isEmpty
  }
  
  public var peek: T? {
    array.first
  }
  
  public mutating func enqueue(_ element: T) -> Bool {
    array.append(element)
    return true
  }
  
  public mutating func dequeue() -> T? {
    isEmpty ? nil : array.removeFirst()
  }
}

extension QueueArray: CustomStringConvertible {
  
  public var description: String {
    String(describing: array)
  }
}

var queue = QueueArray<String>()
queue.enqueue("Ray")
queue.enqueue("Brian")
queue.enqueue("Eric")
queue
queue.dequeue()
queue
queue.peek

练习题

Whose turn is it?

Imagine that you are playing a game of Monopoly with your friends. The problem is that everyone always forget whose turn it is! Create a Monopoly organizer that always tells you whose turn it is. Below is a protocol that you can conform to:

public protocol BoardGameManager {
    
  associatedtype Player
  mutating func nextPlayer() -> Player?
}

extension QueueArray: BoardGameManager {
    
  public typealias Player = T
  
  public mutating func nextPlayer() -> T? {
    guard let person = dequeue() else {
      return nil
    }
    enqueue(person)
    return person
  }
}

var queue = QueueArray<String>()
queue.enqueue("Vincent")
queue.enqueue("Remel")
queue.enqueue("Lukiih")
queue.enqueue("Allison")
print(queue)

print("===== boardgame =======")
queue.nextPlayer()
print(queue)
queue.nextPlayer()
print(queue)
queue.nextPlayer()
print(queue)
queue.nextPlayer()
print(queue)