zebra.rb

################
#  Properties
################
#
# color
# red, green, ivory, blue. yellow

# nationality
# englishman, spaniard, ukrainian, norwegian, japanese

# drinks
# coffee, tea, milk, orange_juice, water

# pets
# dog, snail, horse, fox, zebra

# smoke
# old_gold, kool, chesterfields, lucky_strike, parliaments

################
#  Conditions
################
# 1 There are five houses.
# 2 The Englishman lives in the red house.
# englishman == red
# 3 The Spaniard owns the dog.
# spaniard == dog
# 4 Coffee is drunk in the green house.
# green = coffee
# 5 The Ukrainian drinks tea.
# ukrainian == tea
# 6 The green house is immediately to the right of the ivory house.
# green - ivory == 1
# 7 The Old Gold smoker owns snails.
# old_gold == snail
# 8 Kools are smoked in the yellow house.
# kool == yellow
# 9 Milk is drunk in the middle house.
# milk == 3
# 10 The Norwegian lives in the first house.
# norwegian = 1
# 11 The man who smokes Chesterfields lives in the house next to the man with the fox.
# (chesterfields - fox).abs == 1
# 12 Kools are smoked in a house next to the house where the horse is kept.
# (kool - horse).abs == 1
# 13 The Lucky Strike smoker drinks orange juice.
# lucky_strike == orange_juice
# 14 The Japanese smokes Parliaments.
# japanese == parliaments
# 15 The Norwegian lives next to the blue house.
# (norwegian - blue).abs == 1


## Solution 1, efficient, but too many nesting
orderings = [1, 2, 3, 4, 5].permutation
for colors in orderings do
  red, green, ivory, blue, yellow = colors
  test = green - ivory == 1 # 6 The green house is immediately to the right of the ivory house.
  # print "colors:", red, green, ivory, blue, yellow, "\n" if test
  if test
    for nationalities in orderings do
      englishman, spaniard, ukrainian, norwegian, japanese = nationalities
      test = englishman == red && # 2 The Englishman lives in the red house.
             norwegian == 1 && # 10 The Norwegian lives in the first house.
             (norwegian - blue).abs == 1 # 15 The Norwegian lives next to the blue house.
      # print "nations: ", englishman, spaniard, ukrainian, norwegian, japanese, "\n" if test
      if test
        for drinks in orderings do
          coffee, tea, milk, orange_juice, water = drinks
          test = green == coffee && # 4 Coffee is drunk in the green house.
                 ukrainian == tea && # 5 The Ukrainian drinks tea.
                 milk == 3 # 9 Milk is drunk in the middle house.
          # print "drinks: ", coffee, tea, milk, orange_juice, water, "\n" if test
          if test
            for pets in orderings do
              dog, snail, horse, fox, zebra = pets
              test = spaniard == dog # 3 The Spaniard owns the dog.
              # print "pets: ", dog, snail, horse, fox, zebra, "\n" if test
              if test
                for smokes in orderings do
                  old_gold, kool, chesterfields, lucky_strike, parliaments = smokes

                  test = old_gold == snail && # 7 The Old Gold smoker owns snails.
                         kool == yellow && # 8 Kools are smoked in the yellow house.
                         (chesterfields - fox).abs == 1 && # 11 The man who smokes Chesterfields lives in the house next to the man with the fox.
                         (kool - horse).abs == 1 && # 12 Kools are smoked in a house next to the house where the horse is kept.
                         lucky_strike == orange_juice && # 13 The Lucky Strike smoker drinks orange juice.
                         japanese == parliaments # 14 The Japanese smokes Parliaments.
                  if test
                    puts "final result >>>> "
                    print water, "\n"
                    print zebra, "\n"
                    print "colors:", red, green, ivory, blue, yellow, "\n"
                    print "nations: ", englishman, spaniard, ukrainian, norwegian, japanese, "\n"
                    print "drinks: ", coffee, tea, milk, orange_juice, water, "\n"
                    print "pets: ", dog, snail, horse, fox, zebra, "\n"
                    print "smokes: ", old_gold, kool, chesterfields, lucky_strike, parliaments, "\n"
                  end
                end
              end
            end
          end
        end
      end
    end
  end
end

## Solution 2, but so inefficient, it doesn't so lazy evaluation of lists
orderings = [1, 2, 3, 4, 5].permutation.to_a
orderings.
  product(orderings).
  product(orderings).
  product(orderings).
  product(orderings).each do |colors, nationalities, drinks, pets, smokes|

  red, green, ivory, blue, yellow = colors
  englishman, spaniard, ukrainian, norwegian, japanese = nationalities
  coffee, tea, milk, orange_juice, water = drinks
  old_gold, kool, chesterfields, lucky_strike, parliaments = smokes
  dog, snail, horse, fox, zebra = pets

  if (
    # 1 There are five houses.
    # 2 The Englishman lives in the red house.
    englishman == red &&
    # 3 The Spaniard owns the dog.
    spaniard == dog &&
    # 4 Coffee is drunk in the green house.
    green = coffee &&
    # 5 The Ukrainian drinks tea.
    ukrainian == tea &&
    # 6 The green house is immediately to the right of the ivory house.
    green - ivory == 1 &&
    # 7 The Old Gold smoker owns snails.
    old_gold == snail &&
    # 8 Kools are smoked in the yellow house.
    kool == yellow &&
    # 9 Milk is drunk in the middle house.
    milk == 3 &&
    # 10 The Norwegian lives in the first house.
    norwegian = 1 &&
    # 11 The man who smokes Chesterfields lives in the house next to the man with the fox.
    (chesterfields - fox).abs == 1 &&
    # 12 Kools are smoked in a house next to the house where the horse is kept.
    (kool - horse).abs == 1 &&
    # 13 The Lucky Strike smoker drinks orange juice.
    lucky_strike == orange_juice &&
    # 14 The Japanese smokes Parliaments.
    japanese == parliaments &&
    # 15 The Norwegian lives next to the blue house.
    (norwegian - blue).abs == 1
  )

    print water, "\n", zebra, "\n"
  end
end