225-easy-Implement_Stack_using_Queues.js

/**
225. Implement Stack using Queues

Implement the following operations of a stack using queues.

push(x) -- Push element x onto stack.
pop() -- Removes the element on top of the stack.
top() -- Get the top element.
empty() -- Return whether the stack is empty.
Notes:
You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).
 */

/**
 * Initialize your data structure here.
 */
var MyStack = function () {
  this.stack = [];
};

/**
 * Push element x onto stack.
 * @param {number} x
 * @return {void}
 */
MyStack.prototype.push = function (x) {
  this.stack[this.stack.length] = x;
};

/**
 * Removes the element on top of the stack and returns that element.
 * @return {number}
 */
MyStack.prototype.pop = function () {
  var el = this.stack[this.stack.length - 1];
  var newStack = [];
  for (var i = 0; i < this.stack.length - 1; i++) {
    newStack[i] = this.stack[i];
  }
  this.stack = newStack;
  return el;
};

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

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

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