stack_implemented_with_array.rb

# A very basic Stack implemented with an array

class Stack
  attr_reader :length, :top

  def initialize(size = 1)
    @length = size
    self.reset
  end

  def empty?
    @top.nil?
  end

  def full?
    @top == @length - 1
  end

  def singleton?
    @top == 0
  end

  def push(element)
    raise "Stack Overflow - The stack is full" if self.full?
    if self.empty?
      @top = 0
    else
      @top = @top + 1
    end
    @array[@top] = element
  end

  def pop
    raise "Stack Underflow - The stack is empty" if self.empty?
    x = @array[@top]
    if self.singleton?
      @top = nil
    else
      @top = @top - 1
    end
    return x
  end

  def reset
    @array = Array.new(@length)
    @top = nil
  end
  alias_method :reset!, :reset

  def size
    @array.size
  end

  def first
    @array.first
  end

  def last
    @array[@top]
  end

  def each
    @array.each do
      yield
    end
  end
end