/2/bin_rep.rb 1.9

# # # # # # #
# 'binary representation': store an array of indices in one decimal number
# and vice versa

class Array
  def to_bri # array to integer
    return 0 if self == []

    # first convert indices to a binary number and then use to_i 
    # to convert it to an integer with base 2
    ret = [0] * (self.max + 1)
    self.each do |ele|
      ret[self.max - ele] = 1
    end

    ret.join.to_i(2)
  end
end

class Integer
  def to_bra # integer to array
    ret = []

    # convert the decimal integer to binary form with to_s and base 2 and then
    # check each char to add the current index to the array, if it is set
    self.to_s(2).reverse.chars.each_with_index do |ele,index|
      ret << index if ele == '1'
    end

    ret
  end
end

# Example of use
#
# jl = 584.to_bra  # => [3, 6, 9]
# jl.to_bri        # => 584