0225-implement-stack-using-queues.rb

# frozen_string_literal: true

# 225. Implement Stack using Queues
# Easy
# https://leetcode.com/problems/implement-stack-using-queues

=begin
Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push, top, pop, and empty).

Implement the MyStack class:
* void push(int x) Pushes element x to the top of the stack.
* int pop() Removes the element on the top of the stack and returns it.
* int top() Returns the element on the top of the stack.
* boolean empty() Returns true if the stack is empty, false otherwise.

Notes:
You must use only standard operations of a queue, which means that only push to back, peek/pop from front, size and is empty operations are valid.
Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue's standard operations.

Example 1:
Input
["MyStack", "push", "push", "top", "pop", "empty"]
[[], [1], [2], [], [], []]
Output
[null, null, null, 2, 2, false]
Explanation
MyStack myStack = new MyStack();
myStack.push(1);
myStack.push(2);
myStack.top(); // return 2
myStack.pop(); // return 2
myStack.empty(); // return False

Constraints:
* 1 <= x <= 9
* At most 100 calls will be made to push, pop, top, and empty.
* All the calls to pop and top are valid.
=end

class MyStack
  def initialize
    @stack = []
  end

  def push(x)
    @stack.push(x)
  end

  def pop
    @stack.pop()
  end

  def top
    @stack.last
  end

  def empty
    @stack.empty?
  end
end

# Your MyStack object will be instantiated and called as such:
# obj = MyStack.new()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.top()
# param_4 = obj.empty()