21th December solution - Advent of Code 2020 - swift

december21_1.swift

let allPotIngredients = allergiesToIngredients.map{ $0.value }.reduce(Set<String>()) { (all, set) -> Set<String> in
    all.union(set)
}

let result = foods.map { $0.0.subtracting(allPotIngredients).count }.reduce(0, +)
print(result)

december21_2.swift

var removedAValue = true
while removedAValue {
    removedAValue = false
    for (_, ingredients) in allergiesToIngredients {
        if ingredients.count == 1 {
            for a in allergiesToIngredients {
                let countBefore = a.value.count
                if a.value.count > 1 {
                    let filteredIngredients = a.value.filter { $0 != ingredients.first!}
                    allergiesToIngredients[a.key] = filteredIngredients
                    if countBefore != filteredIngredients.count {
                        removedAValue = true
                    }
                }
            }
        }
    }

}
let sortedByAllergyNames = allergiesToIngredients.sorted { (ele1, ele2) -> Bool in
    ele1.key < ele2.key
}
print(sortedByAllergyNames.map { $0.value.first!}.joined(separator: ","))

december21_shared.swift

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december21.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines).filter { !$0.isEmpty}

var foods = [(Set<String>, Set<String>)]()

for line in lines {
    let parts = line.components(separatedBy: " (contains ")
    let ingredients = parts[0].components(separatedBy: " ")
    let allergies = String(parts[1].dropLast()).components(separatedBy: ", ")
    foods.append((Set(ingredients), Set(allergies)))
}

let allAllergies = foods.map{$1}.reduce(Set<String>()) { (allerges, set) -> Set<String> in
    allerges.union(set)
}

var allergiesToIngredients = [String : Set<String>]()

for allergy in allAllergies {
    var ingredients: Set<String>? = nil
    for food in foods {
        if food.1.contains(allergy) {
            if ingredients == nil {
                ingredients = food.0
            } else {
                ingredients = ingredients?.intersection(food.0)
            }
        }
    }
    allergiesToIngredients[allergy] = ingredients
}