没有数组(年代)

//Javascript stack linked list data structure (no array)

function node(value, noderef) {
    this.value = value;
    this.next = noderef;
}
function stack() {
    this.push = function (value) {
        this.next = this.first;
        this.first = new node(value, this.next);
    }
    this.pop = function () {
        var popvalue = this.first.value;
        this.first = this.first.next;
        return popvalue;
    }
    this.hasnext = function () {
        return this.next != undefined;
    }
    this.isempty = function () {
        return this.first == undefined;
    }

}

//Javascript stack linked list data structure (no array)
function node(value, noderef) {
    this.value = value;
    this.next = undefined;
}
function queue() {
    this.enqueue = function (value) {
        this.oldlast = this.last;
        this.last = new node(value);
        if (this.isempty())
            this.first = this.last;
        else 
           this.oldlast.next = this.last;
    }
    this.dequeue = function () {
        var queuvalue = this.first.value;
        this.first = this.first.next;
        return queuvalue;
    }
    this.hasnext = function () {
        return this.first.next != undefined;
    }
    this.isempty = function () {
        return this.first == undefined;
    }

}

我在实现BFS时遇到了这个线程。在疑惑为何表现如此糟糕之后，我做了一些调查。array.shift()通常在O(n)中运行，这将我的BFS运行时从O(V+E)增加到O(V^2+E)。

我没有从头开始实现一个队列，而是使用了npm包双端队列，它与之前使用的数组方法兼容，工作起来很有魅力。 deque可以用作堆栈或队列。

    //import package
    import Deque from 'double-ended-queue';

    //create queue
    let queue = new Deque();
    //append
    queue.push(item);
    //dequeue (get first item inserted)
    let firstItem = queue.shift();

    //pop (get last item inserted)
    let lastItem = queue.pop();

Javascript中的常规数组结构是一个堆栈(先入后出)，也可以用作队列(先入先出)，这取决于你所做的调用。

检查这个链接，看看如何让一个数组像一个队列:

队列

如果你理解栈的push()和pop()函数，那么queue只是在相反的意义上进行这些操作之一。push()的对边是unshift()， pop()的对边是shift()。 然后:

//classic stack
var stack = [];
stack.push("first"); // push inserts at the end
stack.push("second");
stack.push("last");
stack.pop(); //pop takes the "last" element

//One way to implement queue is to insert elements in the oposite sense than a stack
var queue = [];
queue.unshift("first"); //unshift inserts at the beginning
queue.unshift("second");
queue.unshift("last");
queue.pop(); //"first"

//other way to do queues is to take the elements in the oposite sense than stack
var queue = [];
queue.push("first"); //push, as in the stack inserts at the end
queue.push("second");
queue.push("last");
queue.shift(); //but shift takes the "first" element

下面是一个队列的链表版本，它也包括最后一个节点，这是@perkins建议的，也是最合适的。

// QUEUE Object Definition

var Queue = function() {
  this.first = null;
  this.last = null;
  this.size = 0;
};

var Node = function(data) {
  this.data = data;
  this.next = null;
};

Queue.prototype.enqueue = function(data) {
  var node = new Node(data);

  if (!this.first){ // for empty list first and last are the same
    this.first = node;
    this.last = node;
  } else { // otherwise we stick it on the end
    this.last.next=node;
    this.last=node;
  }

  this.size += 1;
  return node;
};

Queue.prototype.dequeue = function() {
  if (!this.first) //check for empty list
    return null;

  temp = this.first; // grab top of list
  if (this.first==this.last) {
    this.last=null;  // when we need to pop the last one
  }
  this.first = this.first.next; // move top of list down
  this.size -= 1;
  return temp;
};

在我看来，内建数组对于堆栈来说是很好的。如果你想在TypeScript中使用Queue，这里有一个实现

/**
 * A Typescript implementation of a queue.
 */
export default class Queue {

  private queue = [];
  private offset = 0;

  constructor(array = []) {
    // Init the queue using the contents of the array
    for (const item of array) {
      this.enqueue(item);
    }
  }

  /**
   * @returns {number} the length of the queue.
   */
  public getLength(): number {
    return (this.queue.length - this.offset);
  }

  /**
   * @returns {boolean} true if the queue is empty, and false otherwise.
   */
  public isEmpty(): boolean {
    return (this.queue.length === 0);
  }

  /**
   * Enqueues the specified item.
   *
   * @param item - the item to enqueue
   */
  public enqueue(item) {
    this.queue.push(item);
  }

  /**
   *  Dequeues an item and returns it. If the queue is empty, the value
   * {@code null} is returned.
   *
   * @returns {any}
   */
  public dequeue(): any {
    // if the queue is empty, return immediately
    if (this.queue.length === 0) {
      return null;
    }

    // store the item at the front of the queue
    const item = this.queue[this.offset];

    // increment the offset and remove the free space if necessary
    if (++this.offset * 2 >= this.queue.length) {
      this.queue = this.queue.slice(this.offset);
      this.offset = 0;
    }

    // return the dequeued item
    return item;
  };

  /**
   * Returns the item at the front of the queue (without dequeuing it).
   * If the queue is empty then {@code null} is returned.
   *
   * @returns {any}
   */
  public peek(): any {
    return (this.queue.length > 0 ? this.queue[this.offset] : null);
  }

}

这里有一个笑话测试

it('Queue', () => {
  const queue = new Queue();
  expect(queue.getLength()).toBe(0);
  expect(queue.peek()).toBeNull();
  expect(queue.dequeue()).toBeNull();

  queue.enqueue(1);
  expect(queue.getLength()).toBe(1);
  queue.enqueue(2);
  expect(queue.getLength()).toBe(2);
  queue.enqueue(3);
  expect(queue.getLength()).toBe(3);

  expect(queue.peek()).toBe(1);
  expect(queue.getLength()).toBe(3);
  expect(queue.dequeue()).toBe(1);
  expect(queue.getLength()).toBe(2);

  expect(queue.peek()).toBe(2);
  expect(queue.getLength()).toBe(2);
  expect(queue.dequeue()).toBe(2);
  expect(queue.getLength()).toBe(1);

  expect(queue.peek()).toBe(3);
  expect(queue.getLength()).toBe(1);
  expect(queue.dequeue()).toBe(3);
  expect(queue.getLength()).toBe(0);

  expect(queue.peek()).toBeNull();
  expect(queue.dequeue()).toBeNull();
});

希望有人觉得这有用，

欢呼,

Stu