225_implement-queue-using-stacks.js

/**
 * 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.stack2.length) {
    return this.stack2.pop()
  } else {
    while (this.stack1.length) {
      this.stack2.push(this.stack1.pop())
    }
    if (this.stack2.length) {
      return this.stack2.pop()
    } else {
      return null
    }
  }
};

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

/**
 * 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 = new MyQueue()
 * obj.push(x)
 * var param_2 = obj.pop()
 * var param_3 = obj.peek()
 * var param_4 = obj.empty()
 */
var obj = new MyQueue()
obj.push(1)
obj.push(2)
var param_1 = obj.peek()
var param_2 = obj.pop()
var param_3 = obj.peek()
var param_4 = obj.empty()

console.log(param_1, param_2, param_3, param_4)