在JavaScript中实现堆栈和队列的最佳方法是什么?
我想做调车场算法我需要这些数据结构。
当前回答
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;
};
其他回答
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;
}
}
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
单端队列
这是一个使用映射的队列。由于插入顺序得到了保证，所以可以像迭代数组一样迭代它。除此之外，它的思想与Queue.js非常相似。
我做了一些简单的测试，但还没有进行广泛的测试。我还添加了一些我认为很好的功能(通过数组构造)或易于实现(例如last()和first())。
它背后的简单版本/直觉如下:
class Queue {
constructor() {
this.offset = 0
this.data = new Map()
}
enqueue(item) {
const current = this.offset + this.length()
this.data.set(current, item)
}
dequeue() {
if (this.length() > 0) {
this.data.delete(this.offset)
this.offset += 1
}
}
first() {
return this.data.get(this.offset)
}
last() {
return this.data.get(this.offset + this.length() - 1)
}
length() {
return this.data.size
}
}
简单版本的问题是，当内存索引超过9千万亿(Number.MAX_SAFE_INTEGER的值)时，需要重新映射内存。此外，我认为它可能很好有数组构造，它很高兴看到值正在进入队列和退出队列返回。可以通过编写以下代码来解释这一点:
class Queue {
constructor() {
this.offset = 0
this.data = new Map()
if (arguments.length === 1) this._initializeFromArray(arguments[0])
}
enqueue(item) {
const current = this.offset + this.length()
this.data.set(current, item)
let result = this.data.get(current)
this._remapDataIfMaxMemoryViolation(current, Number.MAX_SAFE_INTEGER)
return result
}
dequeue() {
let result = undefined
if (this.length() > 0) {
result = this.data.get(this.offset)
this.data.delete(this.offset)
this.offset += 1
}
if (this.length() === 0) this.offset = 0
return result
}
first() {
return this.data.get(this.offset)
}
last() {
return this.data.get(this.offset + this.length() - 1)
}
length() {
return this.data.size
}
_remapDataIfMaxMemoryViolation(current, threshhold) {
if (current+1 === threshhold) {
const length = this.length()
this.offset = 0
for (const [key, value] of this.data) {
this.data.set(this.offset, value)
this.data.delete(key, value)
this.offset += 1
if (this.offset === length) break
}
}
}
_initializeFromArray(array) {
for (const value of array) {
this.data.set(this.offset, value)
this.offset += 1
}
}
}
我在Chrome开发控制台进行了一些测试，对完整版本进行了以下调用。
l = console.log // I'm lazy with typing
q = new Queue()
l('enqueue', q.enqueue(1))
l('enqueue', q.enqueue(2))
l('enqueue', q.enqueue(3))
l('enqueue', q.enqueue("hello"))
l('enqueue', q.enqueue("monkey"))
l('show 5 elements: ', q.data)
l('length', q.length())
l('first', q.first())
l('last', q.last())
l('dequeue', q.dequeue())
l('dequeue', q.dequeue())
l('show 3 elements', q.data)
q._remapDataIfMaxMemoryViolation(q.length()+q.offset-1, 5)
l('show 3 remapped elements', q.data)
l(queue = new Queue([3,4,5,6,7,8,9]))
l(queue.data)
数组是Javascript中的堆栈。只需使用arr.push(x)和y = arr.pop()。
下面是用Javascript实现队列的最简单方法，对于enqueue(x)和y = dequeue()，它的平摊时间都是O(1)。它使用从插入索引到元素的映射。
function newQueue() {
return {
headIdx: 0,
tailIdx: 0,
elts: {},
enqueue: (elt) => queue.elts[queue.tailIdx++] = elt,
dequeue: () => {
if (queue.headIdx == queue.tailIdx) {
throw new Error("Queue is empty");
}
return queue.elts[queue.headIdx++];
},
size: () => queue.tailIdx - queue.headIdx,
isEmpty: () => queue.tailIdx == queue.headIdx
};
}
使用链表实现的队列比这种基于映射的方法更有效，使用循环缓冲区实现的队列比这种基于映射的方法更有效，但这两种数据结构的实现更复杂(特别是循环缓冲区数据结构)。
有很多方法可以在Javascript中实现堆栈和队列。上面的大多数答案都是非常肤浅的实现，我将尝试实现一些更可读(使用es6的新语法特性)和更健壮的东西。
下面是堆栈实现:
class Stack {
constructor(...items){
this._items = []
if(items.length>0)
items.forEach(item => this._items.push(item) )
}
push(...items){
//push item to the stack
items.forEach(item => this._items.push(item) )
return this._items;
}
pop(count=0){
//pull out the topmost item (last item) from stack
if(count===0)
return this._items.pop()
else
return this._items.splice( -count, count )
}
peek(){
// see what's the last item in stack
return this._items[this._items.length-1]
}
size(){
//no. of items in stack
return this._items.length
}
isEmpty(){
// return whether the stack is empty or not
return this._items.length==0
}
toArray(){
return this._items;
}
}
下面是如何使用堆栈:
let my_stack = new Stack(1,24,4);
// [1, 24, 4]
my_stack.push(23)
//[1, 24, 4, 23]
my_stack.push(1,2,342);
//[1, 24, 4, 23, 1, 2, 342]
my_stack.pop();
//[1, 24, 4, 23, 1, 2]
my_stack.pop(3)
//[1, 24, 4]
my_stack.isEmpty()
// false
my_stack.size();
//3
如果您想查看关于此实现的详细描述以及如何进一步改进，请阅读这里:http://jschap.com/data-structures-in-javascript-stack/
下面是es6中队列实现的代码:
class Queue{
constructor(...items){
//initialize the items in queue
this._items = []
// enqueuing the items passed to the constructor
this.enqueue(...items)
}
enqueue(...items){
//push items into the queue
items.forEach( item => this._items.push(item) )
return this._items;
}
dequeue(count=1){
//pull out the first item from the queue
this._items.splice(0,count);
return this._items;
}
peek(){
//peek at the first item from the queue
return this._items[0]
}
size(){
//get the length of queue
return this._items.length
}
isEmpty(){
//find whether the queue is empty or no
return this._items.length===0
}
}
下面是如何使用这个实现:
let my_queue = new Queue(1,24,4);
// [1, 24, 4]
my_queue.enqueue(23)
//[1, 24, 4, 23]
my_queue.enqueue(1,2,342);
//[1, 24, 4, 23, 1, 2, 342]
my_queue.dequeue();
//[24, 4, 23, 1, 2, 342]
my_queue.dequeue(3)
//[1, 2, 342]
my_queue.isEmpty()
// false
my_queue.size();
//3
要完整地了解如何实现这些数据结构以及如何进一步改进这些数据结构，您可能需要阅读jschap.com上的“在javascript中处理数据结构”系列。这是队列的链接——http://jschap.com/playing-data-structures-javascript-queues/
