Let's Party with Stacks and Queues! Pt 1

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!