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();

这是我的实现堆栈。

function Stack() {
this.dataStore = [];
this.top = 0;
this.push = push;
this.pop = pop;
this.peek = peek;
this.clear = clear;
this.length = length;
}
function push(element) {
this.dataStore[this.top++] = element;
}
function peek() {
return this.dataStore[this.top-1];
}
function pop() {
return this.dataStore[--this.top];
}
function clear() {
this.top = 0;
}
function length() {
return this.top;
}

var s = new Stack();
s.push("David");
s.push("Raymond");
s.push("Bryan");
console.log("length: " + s.length());
console.log(s.peek());

Javascript数组shift()很慢，特别是当包含很多元素时。我知道两种方法来实现平摊O(1)复杂度的队列。

首先是使用循环缓冲区和表加倍。我以前实现过这个。你可以在这里看到我的源代码 https://github.com/kevyuu/rapid-queue

第二种方法是使用两个堆栈。这是带有两个堆栈的队列的代码

function createDoubleStackQueue() {
var that = {};
var pushContainer = [];
var popContainer = [];

function moveElementToPopContainer() {
    while (pushContainer.length !==0 ) {
        var element = pushContainer.pop();
        popContainer.push(element);
    }
}

that.push = function(element) {
    pushContainer.push(element);
};

that.shift = function() {
    if (popContainer.length === 0) {
        moveElementToPopContainer();
    }
    if (popContainer.length === 0) {
        return null;
    } else {
        return popContainer.pop();
    }
};

that.front = function() {
    if (popContainer.length === 0) {
        moveElementToPopContainer();
    }
    if (popContainer.length === 0) {
        return null;
    }
    return popContainer[popContainer.length - 1];
};

that.length = function() {
    return pushContainer.length + popContainer.length;
};

that.isEmpty = function() {
    return (pushContainer.length + popContainer.length) === 0;
};

return that;}

这是使用jsPerf进行的性能比较

CircularQueue.shift() vs Array.shift()

http://jsperf.com/rapidqueue-shift-vs-array-shift

正如你所看到的，大数据集的速度要快得多

你可以使用WeakMaps来实现ES6类中的私有属性，以及JavaScript语言中String属性和方法的好处，如下所示:

const _items = new WeakMap();

class Stack {
  constructor() {
    _items.set(this, []);
  }

push(obj) {
  _items.get(this).push(obj);
}

pop() {
  const L = _items.get(this).length;
  if(L===0)
    throw new Error('Stack is empty');
  return _items.get(this).pop();
}

peek() {
  const items = _items.get(this);
  if(items.length === 0)
    throw new Error ('Stack is empty');
  return items[items.length-1];
}

get count() {
  return _items.get(this).length;
}
}

const stack = new Stack();

//now in console:
//stack.push('a')
//stack.push(1)
//stack.count   => 2
//stack.peek()  => 1
//stack.pop()   => 1
//stack.pop()   => "a"
//stack.count   => 0
//stack.pop()   => Error Stack is empty

var stack = [];
stack.push(2);       // stack is now [2]
stack.push(5);       // stack is now [2, 5]
var i = stack.pop(); // stack is now [2]
alert(i);            // displays 5

var queue = [];
queue.push(2);         // queue is now [2]
queue.push(5);         // queue is now [2, 5]
var i = queue.shift(); // queue is now [5]
alert(i);              // displays 2

摘自“9个你可能不知道的JavaScript技巧”

Create a pair of classes that provide the various methods that each of these data structures has (push, pop, peek, etc). Now implement the methods. If you're familiar with the concepts behind stack/queue, this should be pretty straightforward. You can implement the stack with an array, and a queue with a linked list, although there are certainly other ways to go about it. Javascript will make this easy, because it is weakly typed, so you don't even have to worry about generic types, which you'd have to do if you were implementing it in Java or C#.