Quiz from Professor Stewart's Cabinet of Mathematical Curiosities

alien_encounter.rb

Alien = Struct.new(:name, :species)
species = { Veracitor: :==, Gibberish: :!= }

aliens = %w(Alfy Betty Gemma).product(species.keys).map { |name, sp| Alien[ name, sp ] }

a, b, g = aliens.group_by { |alien| alien.name }.map(&:last)

combinations = a.product(b,g)   # provide all posible combinations of aliens.

desc = ->who_said,left,right{ left.send species[who_said.species], right }

combinations.find do |alfy, betty, gemma|
  x = desc[alfy, betty.species, :Gibberish]     # Alfy said, Betty is Gibberish.
  y = desc[betty, alfy.species, gemma.species]  # Betty said, Alfy is same as Gemma.
  z = desc[gemma, betty.species, :Veracitor]    # Gemma said, Betty is Veracitor.
  x && y && z
end.map { |alien| p "#{alien.name} is #{alien.species}" }

# >> "Alfy is Veracitor"
# >> "Betty is Gibberish"
# >> "Gemma is Gibberish"