Mathematical Magic Trick

magic_trick.rb

# 52-Card Perfect Shuffles - Numberphile
# https://www.youtube.com/watch?v=Y2lXsxmBx7E

module Magic
  class Sys
    class << self
      def ask
        print "I choose: "
        gets.chomp
      end

      def picks
        [*'A'..'Z'].each_with_index.map{|l,i| l+i.to_s }
      end

      def shuffle array, type
        new_array = []
        half = array.length/2
        sliced = array.each_slice(half).to_a
        f_half = sliced.first
        l_half = sliced.last
        half.times do
          shuffled_pair = [f_half.shift, l_half.shift]
          shuffled_pair = shuffled_pair.reverse if type == 1
          new_array << shuffled_pair
        end
        new_array.flatten
      end
    end
  end

  class Trick
    class << self
      def start
        original_picks = Sys.picks

        puts "Pick one:"
        puts original_picks.join(', ')
        number_pick = ask_for_pick original_picks

        puts "Random shuffle'"
        shuffle_picks = original_picks.shuffle
        puts shuffle_picks.join(', ')

        puts "Move #{number_pick} to the front"
        picks = shuffle_picks.unshift shuffle_picks.delete_at(shuffle_picks.index(number_pick))
        puts picks.join(', ')

        puts "Choose a number between 1 and #{picks.count}"
        number = ask_for_number picks.count

        binary = (number-1).to_s(2)
        shuffle_times = binary.split('').map(&:to_i)

        puts "I'll make #{shuffle_times.count} perfect shuffles"
        shuffle_times.each_with_index do |type, index|
          picks = Sys.shuffle picks, type
          puts "Perfect shuffle #{index+1}"
          puts picks.join(', ')
        end

        puts "Pick #{number_pick} should be on position #{number}."
        puts "Pick #{number_pick} is in position #{picks.index(number_pick)+1}."
      end
      
      private
        def ask_for_pick picks
          number_pick = Sys.ask
          unless picks.include?(number_pick)
            puts "Not valid, try again."
            ask_for_pick picks
          end
          number_pick
        end
  
        def ask_for_number picks
          number = Sys.ask.to_i
          unless number.between?(1, picks)
            puts "Not valid, try again."
            ask_for_number picks
          end
          number
        end
    end
  end
end


Magic::Trick.start