232.用栈实现队列.js

/*
 * @lc app=leetcode.cn id=232 lang=javascript
 *
 * [232] 用栈实现队列
 */

// @lc code=start

var MyQueue = function() {
  this.stack1 = [];
  this.stack2 = [];
};

/** 
 * @param {number} x
 * @return {void}
 */
MyQueue.prototype.push = function(x) {
  this.stack1.push(x)
};

/**
 * @return {number}
 */
MyQueue.prototype.pop = function() {
  this.peek();
  return this.stack2.pop();
};

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

/**
 * @return {boolean}
 */
MyQueue.prototype.empty = function() {
  return !this.stack2.length && !this.stack1.length;
};

/**
 * 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()
 */
// @lc code=end