# 232.ImplementQueueusingStacks

// https://leetcode-cn.com/problems/implement-queue-using-stacks/

/**
 * Initialize your data structure here.
 */
var MyQueue = function () {
  this.stack1 = [];
  this.stack2 = [];
};

/**
* Push element x to the back of queue.
* @param {number} x
* @return {void}
*/
MyQueue.prototype.push = function (x) {
  this.stack1.push(x);
};

/**
* Removes the element from in front of queue and returns that element.
* @return {number}
*/
MyQueue.prototype.pop = function () {
  if (this.empty()) {
    return -1;
  }
  if (!this.stack2.length) {
    while (this.stack1.length) {
      var item = this.stack1.pop();
      this.stack2.push(item);
    }
  }
  return this.stack2.pop();
};

/**
* Get the front element.
* @return {number}
*/
MyQueue.prototype.peek = function () {
  if (this.empty()) {
    return -1;
  }
  if (!this.stack2.length) {
    while (this.stack1.length) {
      var item = this.stack1.pop();
      this.stack2.push(item);
    }
  }
  return this.stack2[this.stack2.length - 1];
};

/**
* Returns whether the queue is empty.
* @return {boolean}
*/
MyQueue.prototype.empty = function () {
  return this.stack1.length === 0 && this.stack2.length === 0;
};

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