简单的JS解决方案**

注:我从其他人的评论中获得了一些想法

/* enQueue(q, x) 1) Push x to stack1 (assuming size of stacks is unlimited). deQueue(q) 1) If both stacks are empty then error. 2) If stack2 is empty While stack1 is not empty, push everything from stack1 to stack2. 3) Pop the element from stack2 and return it. */ class myQueue { constructor() { this.stack1 = []; this.stack2 = []; } push(item) { this.stack1.push(item) } remove() { if (this.stack1.length == 0 && this.stack2.length == 0) { return "Stack are empty" } if (this.stack2.length == 0) { while (this.stack1.length != 0) { this.stack2.push(this.stack1.pop()) } } return this.stack2.pop() } peek() { if (this.stack2.length == 0 && this.stack1.length == 0) { return 'Empty list' } if (this.stack2.length == 0) { while (this.stack1.length != 0) { this.stack2.push(this.stack1.pop()) } } return this.stack2[0] } isEmpty() { return this.stack2.length === 0 && this.stack1.length === 0; } } const q = new myQueue(); q.push(1); q.push(2); q.push(3); q.remove() console.log(q)

如何反转堆栈

要理解如何使用两个堆栈构造队列，您应该清楚地了解如何反转堆栈。记住堆叠是如何工作的，它非常类似于你厨房里的盘子堆。最后洗完的盘子会放在干净盘子堆的最上面，这在计算机科学中被称为后进先出(LIFO)。

让我们想象我们的堆栈像一个瓶子，如下所示;

如果我们分别压入整数1,2,3，那么3将在堆栈的顶部。因为1会先被推，然后2会被放在1的上面。最后，将3放在堆栈的顶部，我们的堆栈的最新状态表示为一个瓶子，如下所示;

现在我们的堆栈表示为一个装满值3,2,1的瓶子。我们想要反转堆栈使堆栈顶部的元素为1而堆栈底部的元素为3。我们能做什么?我们可以拿起瓶子，把它倒着拿，这样所有的值都应该按顺序颠倒?

是的，我们可以这样做，但那是一个瓶子。为了完成同样的过程，我们需要有第二个堆栈，它将以相反的顺序存储第一个堆栈元素。让我们把已填充的堆栈放到左边，把新的空堆栈放到右边。为了颠倒元素的顺序，我们将从左堆栈中取出每个元素，并将它们推入右堆栈。你可以在下图中看到我们这样做时发生了什么;

我们知道如何反转堆栈。

使用两个堆栈作为队列

On previous part, I've explained how can we reverse the order of stack elements. This was important, because if we push and pop elements to the stack, the output will be exactly in reverse order of a queue. Thinking on an example, let's push the array of integers {1, 2, 3, 4, 5} to a stack. If we pop the elements and print them until the stack is empty, we will get the array in the reverse order of pushing order, which will be {5, 4, 3, 2, 1} Remember that for the same input, if we dequeue the queue until the queue is empty, the output will be {1, 2, 3, 4, 5}. So it is obvious that for the same input order of elements, output of the queue is exactly reverse of the output of a stack. As we know how to reverse a stack using an extra stack, we can construct a queue using two stacks.

我们的队列模型将由两个堆栈组成。一个堆栈将用于入队操作(左边的堆栈#1，将被称为输入堆栈)，另一个堆栈将用于出队操作(右边的堆栈#2，将被称为输出堆栈)。看看下面的图片;

我们的伪代码如下;

---

入队操作

Push every input element to the Input Stack

出列操作

If ( Output Stack is Empty)
    pop every element in the Input Stack
    and push them to the Output Stack until Input Stack is Empty

pop from Output Stack

---

让我们分别将整数{1,2,3}编入队列。整数将被压入位于左侧的输入堆栈(堆栈#1);

那么如果执行出队列操作会发生什么呢?每当执行出队列操作时，queue将检查输出堆栈是否为空(参见上面的伪代码)。如果输出堆栈为空，则输入堆栈将在输出上提取，因此输入堆栈的元素将反转。在返回值之前，队列的状态如下所示;

检查输出堆栈(堆栈#2)中元素的顺序。很明显，我们可以从输出堆栈中弹出元素，这样输出将与从队列中退出队列时相同。因此，如果我们执行两次出队列操作，首先我们将分别获得{1,2}。那么元素3将是输出堆栈中唯一的元素，而输入堆栈将为空。如果我们将元素4和5编入队列，那么队列的状态将如下所示;

现在输出堆栈不是空的，如果我们执行出队列操作，只有3个将从输出堆栈中弹出。这样的状态如下所示;

同样，如果我们再执行两个出队列操作，在第一个出队列操作时，queue将检查Output Stack是否为空，这是true。然后弹出输入堆栈的元素，并将它们推到输出堆栈，直到输入堆栈为空，然后队列的状态将如下所示;

很容易看出，两个出队列操作的输出将是{4,5}

用两个栈构造队列的实现

下面是Java中的一个实现。我不打算使用现有的Stack实现所以这里的示例将会重新发明轮子;

C - 1) MyStack类:简单的堆栈实现

public class MyStack<T> {

    // inner generic Node class
    private class Node<T> {
        T data;
        Node<T> next;

        public Node(T data) {
            this.data = data;
        }
    }

    private Node<T> head;
    private int size;

    public void push(T e) {
        Node<T> newElem = new Node(e);

        if(head == null) {
            head = newElem;
        } else {
            newElem.next = head;
            head = newElem;     // new elem on the top of the stack
        }

        size++;
    }

    public T pop() {
        if(head == null)
            return null;

        T elem = head.data;
        head = head.next;   // top of the stack is head.next

        size--;

        return elem;
    }

    public int size() {
        return size;
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public void printStack() {
        System.out.print("Stack: ");

        if(size == 0)
            System.out.print("Empty !");
        else
            for(Node<T> temp = head; temp != null; temp = temp.next)
                System.out.printf("%s ", temp.data);

        System.out.printf("\n");
    }
}

C - 2) MyQueue类:使用两个堆栈的队列实现

public class MyQueue<T> {

    private MyStack<T> inputStack;      // for enqueue
    private MyStack<T> outputStack;     // for dequeue
    private int size;

    public MyQueue() {
        inputStack = new MyStack<>();
        outputStack = new MyStack<>();
    }

    public void enqueue(T e) {
        inputStack.push(e);
        size++;
    }

    public T dequeue() {
        // fill out all the Input if output stack is empty
        if(outputStack.isEmpty())
            while(!inputStack.isEmpty())
                outputStack.push(inputStack.pop());

        T temp = null;
        if(!outputStack.isEmpty()) {
            temp = outputStack.pop();
            size--;
        }

        return temp;
    }

    public int size() {
        return size;
    }

    public boolean isEmpty() {
        return size == 0;
    }

}

C - 3)演示代码

public class TestMyQueue {

    public static void main(String[] args) {
        MyQueue<Integer> queue = new MyQueue<>();

        // enqueue integers 1..3
        for(int i = 1; i <= 3; i++)
            queue.enqueue(i);

        // execute 2 dequeue operations 
        for(int i = 0; i < 2; i++)
            System.out.println("Dequeued: " + queue.dequeue());

        // enqueue integers 4..5
        for(int i = 4; i <= 5; i++)
            queue.enqueue(i);

        // dequeue the rest
        while(!queue.isEmpty())
            System.out.println("Dequeued: " + queue.dequeue());
    }

}

C - 4)样品输出

Dequeued: 1
Dequeued: 2
Dequeued: 3
Dequeued: 4
Dequeued: 5

您必须从第一个堆栈中取出所有元素来获取底部元素。然后在每次“出队列”操作时将它们都放回第二个堆栈。

这是我的解决方案在Java使用链表。

class queue<T>{
    static class Node<T>{
        private T data;
        private Node<T> next;
        Node(T data){
            this.data = data;
            next = null;
        }
    }
    Node firstTop;
    Node secondTop;
    
    void push(T data){
        Node temp = new Node(data);
        temp.next = firstTop;
        firstTop = temp;
    }
    
    void pop(){
        if(firstTop == null){
            return;
        }
        Node temp = firstTop;
        while(temp != null){
            Node temp1 = new Node(temp.data);
            temp1.next = secondTop;
            secondTop = temp1;
            temp = temp.next;
        }
        secondTop = secondTop.next;
        firstTop = null;
        while(secondTop != null){
            Node temp3 = new Node(secondTop.data);
            temp3.next = firstTop;
            firstTop = temp3;
            secondTop = secondTop.next;
        }
    }
    
}

注意:在这种情况下，弹出操作非常耗时。因此，我不建议使用两个堆栈创建队列。

// Two stacks s1 Original and s2 as Temp one
    private Stack<Integer> s1 = new Stack<Integer>();
    private Stack<Integer> s2 = new Stack<Integer>();

    /*
     * Here we insert the data into the stack and if data all ready exist on
     * stack than we copy the entire stack s1 to s2 recursively and push the new
     * element data onto s1 and than again recursively call the s2 to pop on s1.
     * 
     * Note here we can use either way ie We can keep pushing on s1 and than
     * while popping we can remove the first element from s2 by copying
     * recursively the data and removing the first index element.
     */
    public void insert( int data )
    {
        if( s1.size() == 0 )
        {
            s1.push( data );
        }
        else
        {
            while( !s1.isEmpty() )
            {
                s2.push( s1.pop() );
            }
            s1.push( data );
            while( !s2.isEmpty() )
            {
                s1.push( s2.pop() );
            }
        }
    }

    public void remove()
    {
        if( s1.isEmpty() )
        {
            System.out.println( "Empty" );
        }
        else
        {
            s1.pop();

        }
    }

下面是使用ES6语法的javascript语言解决方案。

Stack.js

//stack using array
class Stack {
  constructor() {
    this.data = [];
  }

  push(data) {
    this.data.push(data);
  }

  pop() {
    return this.data.pop();
  }

  peek() {
    return this.data[this.data.length - 1];
  }

  size(){
    return this.data.length;
  }
}

export { Stack };

QueueUsingTwoStacks.js

import { Stack } from "./Stack";

class QueueUsingTwoStacks {
  constructor() {
    this.stack1 = new Stack();
    this.stack2 = new Stack();
  }

  enqueue(data) {
    this.stack1.push(data);
  }

  dequeue() {
    //if both stacks are empty, return undefined
    if (this.stack1.size() === 0 && this.stack2.size() === 0)
      return undefined;

    //if stack2 is empty, pop all elements from stack1 to stack2 till stack1 is empty
    if (this.stack2.size() === 0) {
      while (this.stack1.size() !== 0) {
        this.stack2.push(this.stack1.pop());
      }
    }

    //pop and return the element from stack 2
    return this.stack2.pop();
  }
}

export { QueueUsingTwoStacks };

用法如下:

index.js

import { StackUsingTwoQueues } from './StackUsingTwoQueues';

let que = new QueueUsingTwoStacks();
que.enqueue("A");
que.enqueue("B");
que.enqueue("C");

console.log(que.dequeue());  //output: "A"