数据结构与算法每日一题——栈和队列(232. 用栈实现队列)

232. 用栈实现队列

var MyQueue = function() {
   this.stackIn = [];
   this.stackOut = [];
};

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

/**
 * @return {number}
 */
MyQueue.prototype.pop = function() {
   const size = this.stackOut.length;
   if(size) {
       return this.stackOut.pop();
   }
   while(this.stackIn.length) {
       this.stackOut.push(this.stackIn.pop());
   }
   return this.stackOut.pop();
};

/**
 * @return {number}
 */
MyQueue.prototype.peek = function() {
   const x = this.pop();
   this.stackOut.push(x);
   return x;
};

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