Zype Questions

interseccion_arrays.rb

a = [1,2,3,4,5]
b = [2,4,5,9,8,7]
result = []
a.each do |ai|
  result << b.find { |bj| bj == ai }
end
return result

Orden a.length * b.length

lista_encadenada.rb

# Devolver el 3 item empezando desde atras

input = Node(1) -> Node(2) -> Node(3) -> Node(4) -> nil

# Solution using a stack
while input.next() do |node|
  stack.push(node)
end

stack.pop()
stack.pop()
return stack.pop()

# with recursion

def rec(node)
  next = node.next()
  if next
    position = rec(next)
    if position < 3
      return position + 1
    else
      return node.value # At this point I'm in the 3rd position starting from the tail
    end
  else
    return 0 # last item start to count on 0
  end
end


##### THAT Recursion doesn't work but illustrates the idea #####
##### The recursive solution would be this one #####

 def rec(node)
    next_node = node.next()
    if next_node
      counter, result = rec(next_node)
 
      if counter < 2
        return [counter+1, nil]
      elsif counter == 2
        # At this point I'm in the 3rd position starting from the tail
        return [counter+1, node.value]
      else
        return [counter+1, result] # continue counting and but keep forwarding the result back
     end
    else
      # last item start to count in 1
      return [1, nil]
    end
  end
 

switch_smell.rb

#Improve the following code:

   case item_type
   when 'ENTITLED'
     destroy_transaction('purchase')
   when 'CONSUMABLE'
     destroy_transaction('rental')
   when 'SUBSCRIPTION'
     destroy_subscription
   end

# code replace conditional with polymorphism
def create_case_object(item_type)
   # All returned objects comform to the same interface
   case item_type
   when 'ENTITLED'
     EntiledItem.new()
   when 'CONSUMABLE'
     Consumable.new()
   when 'SUBSCRIPTION'
     Subscrioption.new()
   end
end

item = create_case_object('ENTITLED')
item.destroy_transaction # no matter which object it returns I can call `destroy_transaction` over it

class Item
  def destroy_transaction(param)
     ...
  end
end

class EntiledItem < Item
  def destroy_transaction(param)
    super('purchase')
  end
end

class ConsumableItem < Item
  def destroy_transaction(param)
     super('rental')
  end
end

class Subscription < Item
  def destroy_transaction(param)
     # destroy_subscription behaviour
  end
end