swift 创建队列(queue)

/// 队列 queue
// 用数组来实现队列内部的线性表
public struct Queue<T> {
    fileprivate var queueArray = [T]()
    
    public var count: Int {
        return queueArray.count
    }
    
    public var isEmpty: Bool {
        return queueArray.isEmpty
    }
    
    // 前面的元素
    public var front: T? {
        if isEmpty {
            print("queue is empty")
            return nil
        } else {
            return queueArray.first
        }
    }
    
    // 添加元素
    public mutating func enqueue(_ element: T) {
        queueArray.append(element)
    }
    
    // 移除元素
    public mutating func dequeue() -> T? {
        if isEmpty {
            print("queue is empty")
            return nil
        } else {
            return queueArray.removeFirst()
        }
    }
    
    // 打印元素
    public mutating func printAllElements() {
        guard count > 0 else {
            print("queue is empty")
            return
        }
        
        print("nprint all queue elements:")
        for (index, value) in queueArray.enumerated() {
            print("[(index)](value)")
        }
    }
        
}

// 使用队列
var queue = Queue.init(queueArray: [])
queue.isEmpty
queue.printAllElements()
queue.count
queue.enqueue("abc")
queue.printAllElements()
queue.enqueue("xyz")
queue.printAllElements()
queue.front