Add example solution

exercises/practice/zebra-puzzle/.meta/example.rb

@@ -0,0 +1,150 @@
+CATEGORIES = {
+  color: %i[
+    red
+    green
+    blue
+    yellow
+    ivory
+  ].freeze,
+  nationality: %i[
+    englishman
+    spaniard
+    ukrainian
+    norwegian
+    japanese
+  ].freeze,
+  beverage: %i[
+    coffee
+    tea
+    milk
+    orange_juice
+    water
+  ].freeze,
+  cigarette: %i[
+    old_gold
+    kool
+    chesterfield
+    lucky_strike
+    parliament
+  ].freeze,
+  pet: %i[
+    dog
+    snails
+    fox
+    horse
+    zebra
+  ].freeze
+}.freeze
+
+House = Data.define(*CATEGORIES.keys)
+
+module ZebraPuzzle
+  def self.water_drinker
+    houses.find { _1.beverage == :water }.nationality.to_s.capitalize
+  end
+
+  def self.zebra_owner
+    houses.find { _1.pet == :zebra }.nationality.to_s.capitalize
+  end
+
+  private_class_method def self.houses
+    @houses ||= ZebraPuzzleSolver.new.final_row_of_houses
+  end
+end
+
+class ZebraPuzzleSolver
+  def initialize
+    @table = null_table
+  end
+
+  def final_row_of_houses
+    return @table unless @table == null_table
+
+    CATEGORIES.each_key do |key|
+      add_into_table!(key)
+      send("filter_by_#{key}!")
+    end
+
+    raise "More than one final possibility exists" if @table.count > 1
+
+    @table.first
+  end
+
+  private
+  def null_table
+    null_house = CATEGORIES.keys.to_h { |key| [key, nil] }
+
+    # Clue: There are five houses.
+    [[null_house] * 5]
+  end
+
+  def add_into_table!(new_key)
+    permutations = CATEGORIES.fetch(new_key).permutation
+
+    @table.map! do |houses|
+      permutations.map do |new_values|
+        houses.zip(new_values).map do |house, new_value|
+          House.new(**house.to_h.merge(new_key => new_value))
+        end
+      end
+    end.flatten!(1)
+  end
+
+  def filter_by_color!
+    @table.select! do |houses|
+      # Clue: The green house is immediately to the right of the ivory house.
+      houses.index { _1.color == :green } == houses.index { _1.color == :ivory } + 1 &&
+        # (Clue: The second house is blue. From these clues:)
+        #   - The Norwegian lives in the first house.
+        #   - The Norwegian lives next to the blue house.
+        houses.index { _1.color == :blue } == 1
+    end
+  end
+
+  def filter_by_nationality!
+    @table.select! do |houses|
+      # Clue: The Englishman lives in the red house.
+      houses.any? { _1.nationality == :englishman && _1.color == :red } &&
+        # Clue: The Norwegian lives in the first house.
+        houses.first.nationality == :norwegian
+    end
+  end
+
+  def filter_by_beverage!
+    @table.select! do |houses|
+      # Clue: Coffee is drunk in the green house.
+      houses.any? { _1.beverage == :coffee && _1.color == :green } &&
+        # Clue: The Ukrainian drinks tea.
+        houses.any? { _1.nationality == :ukrainian && _1.beverage == :tea } &&
+        # Clue: Milk is drunk in the middle house.
+        houses[2].beverage == :milk
+    end
+  end
+
+  def filter_by_cigarette!
+    @table.select! do |houses|
+      # Clue: Kools are smoked in the yellow house.
+      houses.any? { _1.cigarette == :kool && _1.color == :yellow } &&
+        # Clue: The Lucky Strike smoker drinks orange juice.
+        houses.any? { _1.cigarette == :lucky_strike && _1.beverage == :orange_juice } &&
+        # Clue: The Japanese smokes Parliaments.
+        houses.any? { _1.nationality == :japanese && _1.cigarette == :parliament }
+    end
+  end
+
+  # rubocop:disable Metrics/AbcSize
+
+  def filter_by_pet!
+    @table.select! do |houses|
+      # Clue: The Spaniard owns the dog.
+      houses.any? { _1.nationality == :spaniard && _1.pet == :dog } &&
+        # Clue: The Old Gold smoker owns snails.
+        houses.any? { _1.cigarette == :old_gold && _1.pet == :snails } &&
+        # Clue: The man who smokes Chesterfields lives in the house next to the man with the fox.
+        (houses.index { _1.cigarette == :chesterfield } - houses.index { _1.pet == :fox }).abs == 1 &&
+        # Clue: Kools are smoked in the house next to the house where the horse is kept.
+        (houses.index { _1.cigarette == :kool } - houses.index { _1.pet == :horse }).abs == 1
+    end
+  end
+  # rubocop:enable Metrics/AbcSize
+end