92 lines
2.6 KiB
Swift
92 lines
2.6 KiB
Swift
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import Foundation
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let input = loadData(day: 21)
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let scanner = Scanner(string: input)
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scanner.charactersToBeSkipped = .whitespaces
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extension Scanner {
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func ingredient() -> String? {
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scanUpToCharacters(from: .whitespaces)
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}
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func allergens() -> Set<String>? {
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guard string("(contains") else { return nil }
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var result: Set<String> = []
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let end = CharacterSet(charactersIn: ",)")
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repeat {
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guard let allergen = scanUpToCharacters(from: end) else { return nil }
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result.insert(allergen)
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} while string(",")
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guard string(")") else { return nil }
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return result
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}
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func end() -> Set<String>? {
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let allergens = self.allergens()
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guard string("\n") else { return nil }
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return allergens ?? []
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}
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typealias Food = (ingredients: Set<String>, allergens: Set<String>)
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func food() -> Food? {
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var ingredients = Set<String>()
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while true {
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guard let ingredient = self.ingredient() else { return nil }
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ingredients.insert(ingredient)
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if let end = self.end() {
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return (ingredients, end)
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}
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}
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}
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func foods() -> [Food] {
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var result: [Food] = []
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while !isAtEnd, let food = self.food() {
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result.append(food)
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}
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return result
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}
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}
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let data = scanner.foods()
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var possibleIngredientsByAllergen: [String: Set<String>] = [:]
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var allIngredients: Set<String> = []
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var allergens: [(String, String)] = []
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for (ingredients, allergens) in data {
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allIngredients.formUnion(ingredients)
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for allergen in allergens {
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if let possible = possibleIngredientsByAllergen[allergen] {
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possibleIngredientsByAllergen[allergen] = possible.intersection(ingredients)
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} else {
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possibleIngredientsByAllergen[allergen] = ingredients
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}
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}
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}
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while !possibleIngredientsByAllergen.isEmpty {
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for (allergen, possible) in possibleIngredientsByAllergen where possible.count == 1 {
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let ingredient = possible.first!
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allIngredients.remove(ingredient)
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possibleIngredientsByAllergen.removeValue(forKey: allergen)
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allergens.append((allergen, ingredient))
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for key in possibleIngredientsByAllergen.keys {
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possibleIngredientsByAllergen[key]?.remove(ingredient)
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}
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}
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}
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let count = data.reduce(0) { $0 + $1.ingredients.intersection(allIngredients).count }
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print("part 1:", count)
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let canonicalDangerousList = allergens
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.sorted { $0.0 < $1.0 }
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.map { $0.1 }
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.joined(separator: ",")
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print("part 2:", canonicalDangerousList)
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