class_and_exp_challenge.rb

class Allergies 
    def initialize(num)
        @allergy_num = num
        @allergy_list = ['eggs', 'peanuts', 'shellfish', 'strawberries', 'tomatoes', 'chocolate', 'pollen', 'cats']
        @exp = @allergy_list.count
        @my_allergies = []
        get_allergies(num)
    end

    def list
        return @my_allergies
    end

    def get_allergies(num)
        if num > (2 ** @exp)
            @my_allergies << @allergy_list[@exp]
            @exp -= 1
            get_allergies(num - (2 ** (@exp+1)))
        elsif (num < (2 ** @exp))
            @exp -= 1
            get_allergies(num)
        else
            @my_allergies << @allergy_list[@exp]
        end
    end
    def allergic_to?(str)
        @my_allergies.include?(str)
    end
end

# instances
allergies1 = Allergies.new(34)
print allergies1.list
puts
allergies2 = Allergies.new(129)
print allergies2.list
puts
puts allergies1.allergic_to?('shellfish')
puts allergies1.allergic_to?('cats')
puts allergies1.allergic_to?('chocolate') 

# explanation 
# we initialize num with a score of 34
# we call the get_allergies method within .new 
# we enter the get allergies method 
# the first condition fails (34 is less than 2**8)
# the second condition is true 
# we reduce the exp (to 7) and we call the method again 
# we enter the get allergies method 
# the first condition fails (34 is less than 2**7)
# the second condition is true 
# we reduce the exp (to 6) and we call the method again 
# we enter the get allergies method 
# the first condition fails (34 is less than 2**6)
# the second condition is true 
# we reduce the exp (to 5) and we call the method again 
# we enter the get allergies method 
# the first condition is true (34 is more than 2**5)
# we pass in the 5th element of our allergy_list (chocolate) into the new array 
# we reduce the exp (to 4)
# we call the method again, the num is minus by 2 to the power exp(4 + 1)
# sum = 34 - 32
# num = 2
# num is reassigned to become 2 
# we enter the get allergies method 
# the first condition fails (2 is less than 2**4)
# the second condition is true 
# we reduce the exp (to 3) and we call the method again 
# we enter the get allergies method
# the first condition fails (2 is less than 2**3)
# we reduce the exp (to 2) and we call the method again 
# we enter the get allergies method
# the first condition fails (2 is less than 2**2)
# we reduce the exp (to 1) and we call the method again 
# we enter the get allergies method
# the first condition is false (2 is not less than 2**1)
# the second condition is false (2 is not more than 2**1)
# we run the else condition
# we pass the 1st element of our allergies list (peanuts) into the new array 
# we exit the conditional