Day 21: Part 1

Signed-off-by: James Griffin <james@unsupervised.ca>

twentyone/day_twentyone.go

@@ -0,0 +1,127 @@
+package twentyone
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+type food struct {
+	ingredients map[string]bool
+	allergens   []string
+}
+
+type list struct {
+	foods                       []food
+	allergens                   map[string]bool
+	possibleIngredientAllergens map[string][]string
+}
+
+func (l *list) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	l.allergens = map[string]bool{}
+	l.possibleIngredientAllergens = map[string][]string{}
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		f := food{
+			ingredients: map[string]bool{},
+			allergens:   []string{},
+		}
+		foodParts := strings.Split(scanner.Text(), " (contains ")
+		if len(foodParts) != 2 {
+			return fmt.Errorf("Unable to parse %s", scanner.Text())
+		}
+		ingredients := strings.Split(foodParts[0], " ")
+		for _, i := range ingredients {
+			f.ingredients[i] = true
+			l.possibleIngredientAllergens[i] = []string{}
+		}
+
+		allergens := strings.Split(foodParts[1], ")")
+		f.allergens = strings.Split(allergens[0], ", ")
+		for _, a := range f.allergens {
+			l.allergens[a] = true
+		}
+
+		l.foods = append(l.foods, f)
+	}
+
+	return nil
+}
+
+func (l *list) isolateIngredientAllergens() {
+	// For each allergen iterate through the foods to find the possible ingredients
+	for allergen := range l.allergens {
+		possibleFoods := []food{}
+		possibleIngredients := map[string]bool{}
+
+		// Check food for allergen
+		for _, f := range l.foods {
+			for _, a := range f.allergens {
+				if allergen == a {
+					possibleFoods = append(possibleFoods, f)
+					for i := range f.ingredients {
+						possibleIngredients[i] = true
+					}
+				}
+			}
+		}
+
+		// Go through foods and eliminate ingredients that aren't present
+		for _, p := range possibleFoods {
+			for pi := range possibleIngredients {
+				if !p.ingredients[pi] {
+					possibleIngredients[pi] = false
+				}
+			}
+		}
+
+		for i, cause := range possibleIngredients {
+			if cause {
+				l.possibleIngredientAllergens[i] = append(l.possibleIngredientAllergens[i], allergen)
+			}
+		}
+	}
+}
+
+func (l *list) countAllergenFreeAppearances() (int, []string) {
+	count := 0
+
+	// Find allergen free ingredients
+	ingredients := []string{}
+	for ingredient, allergens := range l.possibleIngredientAllergens {
+		if len(allergens) == 0 {
+			ingredients = append(ingredients, ingredient)
+		}
+	}
+
+	// Count the appearances of the allergen free ingredients in all foods
+	for _, i := range ingredients {
+		for _, f := range l.foods {
+			for ingredient := range f.ingredients {
+				if i == ingredient {
+					count++
+				}
+			}
+		}
+	}
+
+	return count, ingredients
+}
+
+// PartOne How many times do allergen free ingredients appear
+func PartOne() string {
+	l := list{}
+	l.load("twentyone/input.txt")
+
+	l.isolateIngredientAllergens()
+	count, ingredients := l.countAllergenFreeAppearances()
+	return fmt.Sprintf("There are %d appearances of %d allergen free ingredients", count, len(ingredients))
+}