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Cover image for Let's Party with Stacks and Queues! Pt 1

Let's Party with Stacks and Queues! Pt 1

msarit profile image Arit Amana Updated on ・3 min read

I have consumed several excellent written/video tutorials on Stacks and Queues, with their characteristics and limitations. However, I haven't seen many examples where these 2 data structures are implemented beyond defining their class and associated methods.

So I've created a Ruby tutorial that implements stacks and queues within an example where meals are served to a line of guests at a party!

In this tutorial, we will create a short program that takes two arrays (Stack of Meals, and Queue of Guests) and advances the queue based on whether the top meal matches the culinary preferences of the first guest in the queue.

Sound like fun? Let's dive in!


Let's build the MealStack class first. This class will accept an array of meals (meals_array) identified by their type (such as 'vegetarian', 'regular', 'vegan').

class Stack
  attr_accessor :meals

  def initialize(meals_array)
    self.meals = meals_array
  end
end

We want to be able to do the following with a MealStack:

  • See what meal is at the top of the stack (top_meal), which is the last item in the array:
    def top_meal
        meals.last
    end
  • Take the top meal off the stack (take_meal):
    def take_meal
        meals.pop
    end
  • Know if all meals are gone (stack_empty?):
    def stack_empty?
        meals.empty?
    end
  • View all remaining meals in the stack (display_meals). We call .reverse on meals so that the last array entry appears first (as the top of the stack):
    def display_meals
        meals.reverse.inspect
    end
  • Know how many meals are in the stack (size):
    def size
        meals.length
    end

Here is the complete MealStack class:

class MealStack
  attr_accessor :meals

  def initialize(meals_array)
    meals = meals_array
  end

  def top_meal
    meals.last
  end

  def take_meal
    meals.pop
  end

  def stack_empty?
    meals.empty?
  end

  def display_meals
    meals.reverse.inspect
  end

  def size
    meals.length
  end
end

Now let's build the GuestQueue class, which accepts an array of guests identified by their meal preference. For simplicity's sake, guests' meal preferences are identified same as the meals array - 'vegetarian', 'vegan', etc.

class GuestQueue
  attr_accessor :guests

  def initialize(guest_array)
    self.guests = guest_array
  end
end

We want to be able to do the following with a QueueStack:

  • Know who is at the front of the queue (first_guest):
 def first_guest
    guests.first
 end
  • Have guests able to join the queue (join_queue(guest)):
 def join_queue(guest)
    guests.push(guest)
  end
  • Have guests able to leave the queue (leave_queue):
 def leave_queue
    guests.shift
  end
  • Have guests able to rejoin the queue (rejoin_queue):
    def rejoin_queue
        join_queue(leave_queue)
    end
  • Know if all guests have been served (queue_empty?):
    def queue_empty?
        guests.empty?
    end
  • View all remaining guests in the queue (display_queue):
    def display_queue
        guests.inspect
    end
  • Know how many guests are in the queue (size):
    def size
        guests.length
    end

Here is the complete GuestQueue class:

class GuestQueue
    attr_accessor :guests

    def initialize(guest_array)
        self.guests = guest_array
    end

    def first_guest
        guests.first
    end

    def join_queue(guest)
        guests.push(guest)
    end

    def leave_queue
        guests.shift
    end

    def rejoin_queue
        join_queue(leave_queue)
    end

    def queue_empty?
        guests.empty?
    end

    def display_queue
        guests.inspect
    end

    def size
        guests.length
    end
end

Finally, let's make sure our MealStack and GuestQueue classes work:

my_meals = MealStack.new(%w[vegetarian vegan normal paleo vegan normal paleo])

puts my_meals.size # 7
puts my_meals.top_meal # paleo
puts my_meals.take_meal # paleo
puts my_meals.stack_empty? # false
puts my_meals.take_meal # normal
puts my_meals.take_meal # vegan
puts my_meals.size # 4

- - -

my_friends = GuestQueue.new(%w[normal paleo vegan vegetarian vegan normal paleo])

puts my_friends.size # 7
puts my_friends.first_guest # normal
puts my_friends.leave_queue # normal
puts my_friends.leave_queue # paleo
puts my_friends.size # 5
puts my_friends.rejoin_queue # vegan
puts my_friends.leave_queue # vegetarian
puts my_friends.first_guest # vegan

In the next part, things get interesting when we build our Party class!

Posted on by:

msarit profile

Arit Amana

@msarit

Former Public Health Analyst. Coding Bootcamp Grad. Mentor to women (especially moms) who are transitioning to tech careers.

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