使用栈实现队列的下列操作：

push(x) -- 将一个元素放入队列的尾部。
pop() -- 从队列首部移除元素。
peek() -- 返回队列首部的元素。
empty() -- 返回队列是否为空。
示例:

MyQueue queue = new MyQueue();

queue.push(1);
queue.push(2);
queue.peek(); // 返回 1
queue.pop(); // 返回 1
queue.empty(); // 返回 false
说明:

你只能使用标准的栈操作 -- 也就是只有 push to top, peek/pop from top, size, 和 is empty 操作是合法的。
你所使用的语言也许不支持栈。你可以使用 list 或者 deque（双端队列）来模拟一个栈，只要是标准的栈操作即可。
假设所有操作都是有效的、 （例如，一个空的队列不会调用 pop 或者 peek 操作）。

/*
 * @lc app=leetcode id=232 lang=javascript
 *
 * [232] Implement Queue using Stacks
 */
/**
 * Initialize your data structure here.
 */
var MyQueue = function () {
  // tag: queue stack array
  this.stack = [];
  this.helperStack = [];
};

/**
 * Push element x to the back of queue.
 * @param {number} x
 * @return {void}
 */
MyQueue.prototype.push = function (x) {
  let cur = null;
  while ((cur = this.stack.pop())) {
    this.helperStack.push(cur);
  }
  this.helperStack.push(x);

  while ((cur = this.helperStack.pop())) {
    this.stack.push(cur);
  }
};

/**
 * Removes the element from in front of queue and returns that element.
 * @return {number}
 */
MyQueue.prototype.pop = function () {
  return this.stack.pop();
};

/**
 * Get the front element.
 * @return {number}
 */
MyQueue.prototype.peek = function () {
  return this.stack[this.stack.length - 1];
};

/**
 * Returns whether the queue is empty.
 * @return {boolean}
 */
MyQueue.prototype.empty = function () {
  return this.stack.length === 0;
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * var obj = new MyQueue()
 * obj.push(x)
 * var param_2 = obj.pop()
 * var param_3 = obj.peek()
 * var param_4 = obj.empty()
 */

class MyQueue:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.stack = []
        self.help_stack = []

    def push(self, x: int) -> None:
        """
        Push element x to the back of queue.
        """
        while self.stack:
            self.help_stack.append(self.stack.pop())
        self.help_stack.append(x)
        while self.help_stack:
            self.stack.append(self.help_stack.pop())

    def pop(self) -> int:
        """
        Removes the element from in front of queue and returns that element.
        """
        return self.stack.pop()

    def peek(self) -> int:
        """
        Get the front element.
        """
        return self.stack[-1]

    def empty(self) -> bool:
        """
        Returns whether the queue is empty.
        """
        return not bool(self.stack)


# Your MyQueue object will be instantiated and called as such:
# obj = MyQueue()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.peek()
# param_4 = obj.empty()

class MyQueue {
    Stack<Integer> pushStack = new Stack<> ();
    Stack<Integer> popStack = new Stack<> ();

    /** Initialize your data structure here. */
    public MyQueue() {

    }

    /** Push element x to the back of queue. */
    public void push(int x) {
        while (!popStack.isEmpty()) {
            pushStack.push(popStack.pop());
        }
        pushStack.push(x);
    }

    /** Removes the element from in front of queue and returns that element. */
    public int pop() {
        while (!pushStack.isEmpty()) {
            popStack.push(pushStack.pop());
        }
        return popStack.pop();
    }

    /** Get the front element. */
    public int peek() {
        while (!pushStack.isEmpty()) {
            popStack.push(pushStack.pop());
        }
        return popStack.peek();
    }

    /** Returns whether the queue is empty. */
    public boolean empty() {
        return pushStack.isEmpty() && popStack.isEmpty();
    }
}

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue obj = new MyQueue();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.peek();
 * boolean param_4 = obj.empty();
 */