aoc2020/day21/day21.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"sort"
	"strings"
)

type dish struct {
	ingredients []string
	allergens   []string
}

func readDish(line string) dish {
	var food dish
	parts := strings.Split(line, " (contains ")
	if len(parts) != 2 {
		log.Fatalf("Invalid line: %s", line)
	}

	for _, ing := range strings.Split(parts[0], " ") {
		food.ingredients = append(food.ingredients, ing)
	}

	cleanedPart2 := strings.TrimSuffix(parts[1], ")")
	for _, allergen := range strings.Split(cleanedPart2, ", ") {
		food.allergens = append(food.allergens, allergen)
	}

	return food
}

func readFile(file *os.File) []dish {
	var foods []dish
	scanner := bufio.NewScanner(file)

	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			break
		}

		foods = append(foods, readDish(line))
	}
	if err := scanner.Err(); err != nil {
		log.Fatalf("Scanner error: %s", err)
	}

	return foods
}

type alerg struct {
	count       int
	ingredients map[string]int
}

func processFoods(foods []dish) map[string]alerg {
	allergensPossibleForIngredients := make(map[string]alerg)

	for _, food := range foods {
		for _, allergen := range food.allergens {
			var currentAllergen alerg
			if _, ok := allergensPossibleForIngredients[allergen]; !ok {
				currentAllergen = alerg{count: 0, ingredients: make(map[string]int)}
			} else {
				currentAllergen = allergensPossibleForIngredients[allergen]
			}

			currentAllergen.count++
			for _, ingredient := range food.ingredients {
				currentAllergen.ingredients[ingredient]++
			}

			allergensPossibleForIngredients[allergen] = currentAllergen
		}
	}

	return allergensPossibleForIngredients
}

func findAllergicIngredients(allergensPossibleForIngredients map[string]alerg) map[string][]string {
	highestAllergens := make(map[string][]string)

	for allergen, item := range allergensPossibleForIngredients {
		var highestIngredients []string

		for key, value := range item.ingredients {
			if value == item.count {
				highestIngredients = append(highestIngredients, key)
			}
		}

		highestAllergens[allergen] = highestIngredients
	}

	return highestAllergens
}

func analyse(highestAllergens map[string][]string) map[string]string {
	foundIngredients := make(map[string]string)
	found := 0
	target := len(highestAllergens)

	for found < target {
		currentAllergens := make(map[string][]string)
		for key, value := range highestAllergens {
			if len(value) == 1 {
				foundIngredients[value[0]] = key
				found++
				continue
			}

			var newList []string
			for _, item := range value {
				if _, ok := foundIngredients[item]; ok {
					continue
				}

				newList = append(newList, item)
			}

			currentAllergens[key] = newList
		}

		highestAllergens = currentAllergens
	}

	return foundIngredients
}

func part1(foods []dish, badIngredients map[string]string) int {
	sum := 0

	for _, food := range foods {
		for _, ingredient := range food.ingredients {
			if _, ok := badIngredients[ingredient]; !ok {
				sum++
			}
		}
	}

	return sum
}

func part2(badIngredients map[string]string) string {
	allergenIngredient := make(map[string]string)
	var keys []string

	for key, value := range badIngredients {
		allergenIngredient[value] = key
		keys = append(keys, value)
	}

	sort.Strings(keys)

	var results []string
	for _, key := range keys {
		results = append(results, allergenIngredient[key])
	}

	return strings.Join(results, ",")
}

func main() {
	if len(os.Args) < 2 {
		log.Fatal("You need to specify a file!")
	}

	filePath := os.Args[1]
	file, err := os.Open(filePath)
	if err != nil {
		log.Fatalf("Failed to open %s!\n", filePath)

	}

	foods := readFile(file)
	if err := file.Close(); err != nil {
		log.Fatalf("Failed to close file: %s", err)
	}

	allergens := processFoods(foods)
	highestAllergens := findAllergicIngredients(allergens)
	badIngredients := analyse(highestAllergens)

	fmt.Println("Part1:", part1(foods, badIngredients))
	fmt.Println("Part2:", part2(badIngredients))
}