adventofcode/2020/day21.go

package main

import (
	"fmt"
	"os"
	"regexp"
	"sort"
	"strings"

	"git.annabunch.es/annabunches/adventofcode/2020/lib/util"
)

// could optimize this better with maps, but we'll just do this. Our data set should be small enough
func intersection(a, b []string) (result []string) {
	result = make([]string, 0)
	for _, av := range a {
		for _, bv := range b {
			if av == bv {
				result = append(result, av)
				break
			}
		}
	}
	return
}

func includes(list []string, item string) bool {
	for _, cmp := range list {
		if cmp == item {
			return true
		}
	}
	return false
}

func remove(list []string, item string) []string {
	for i, cmp := range list {
		if cmp == item {
			return append(list[:i], list[i+1:]...)
		}
	}
	return list
}

func parseInput(input []string) (ingredients map[string]int, allergens map[string][]string) {
	re := regexp.MustCompile("^(.*) \\(contains (.*)\\)")
	allergens = make(map[string][]string)
	ingredients = make(map[string]int)
	for _, line := range input {
		data := re.FindStringSubmatch(line)
		is := strings.Split(data[1], " ")
		as := strings.Split(data[2], ", ")

		for _, ingredient := range is {
			ingredients[ingredient]++
		}

		for _, allergen := range as {
			if ingredients, ok := allergens[allergen]; ok {
				allergens[allergen] = intersection(is, ingredients)
			} else {
				allergens[allergen] = is
			}
		}
	}

	return
}

func findUniqueSolution(aMap map[string][]string) {
	done := false
	for !done {
		done = true
		for a1, is1 := range aMap {
			if len(is1) == 1 {
				ingredient := is1[0]
				for a2, is2 := range aMap {
					if a1 == a2 {
						continue
					}
					aMap[a2] = remove(is2, ingredient)
				}
			}
		}

		for _, is := range aMap {
			if len(is) > 1 {
				done = false
				break
			}
		}
	}
}

func main() {
	step := os.Args[1]
	values := util.InputParserStrings(os.Args[2])
	ingredients, allergenMap := parseInput(values)

	switch step {
	case "1":
		loose := make([]string, 0)
		for ingredient, _ := range ingredients {
			found := false
			for _, is := range allergenMap {
				if includes(is, ingredient) {
					found = true
					break
				}
			}
			if !found {
				loose = append(loose, ingredient)
			}
		}

		total := 0
		for _, i := range loose {
			total += ingredients[i]
		}
		fmt.Println(total)
	case "2":
		findUniqueSolution(allergenMap)
		keys := make([]string, 0)
		for k, _ := range allergenMap {
			keys = append(keys, k)
		}
		result := ""
		sort.Strings(keys)
		for _, k := range keys {
			result = result + "," + allergenMap[k][0]
		}
		fmt.Println(strings.Trim(result, ","))
	}
}