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advent-of-code/2020/ruby/day_21.rb

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require "set"
Food = Struct.new(:id, :ingredients, :allergens)
foods = ARGF.read
.scan(/(.+) \(contains (.+)\)/)
.map.with_index {|(ingredients, allergens), i|
ingredients, allergens = [ ingredients.split(" "), allergens.split(", ") ].map {|x| Set.new(x) }
Food.new(i, ingredients, allergens)
}
all_ingredients = foods.map(&:ingredients).inject(&:|)
all_allergens = foods.map(&:allergens).inject(&:|)
no_allergens = all_ingredients.select {|ingredient|
possible_allergens = foods
.select {|food| food.ingredients.include?(ingredient) }
.map(&:allergens)
.inject(&:|)
possible_allergens.none? {|allergen|
foods_with_allergen = foods.select {|f| f.allergens.include?(allergen) }
foods_with_allergen.all? {|f| f.ingredients.include?(ingredient) }
}
}
# part one
# p foods.map {|f| f.ingredients.count {|i| no_allergens.include?(i) }}.sum
known, unknown = all_allergens.map {|a|
[a, foods.select {|f| f.allergens.include?(a) }.map(&:ingredients).inject(&:&) ]
}.to_h.partition {|_,v| v.size == 1 }.map(&:to_h)
until unknown.empty?
unknown.transform_values! {|v| v - known.values.inject(&:|) }
new_known, unknown = unknown.partition {|_,v| v.size == 1 }.map(&:to_h)
known.merge!(new_known)
end
p known.transform_values {|v| v.to_a.first }.sort_by(&:first).map(&:last).join(?,)