refactor: prepare part two, which will use the same parsing logic + new structure

internal/2020/DaySeven/code.go

@@ -4,22 +4,26 @@ import (
 	"advent-of-code/internal/registry"
 	"os"
 	"regexp"
+	"strconv"
 	"strings"
 )
 
+var (
+	rulePattern      = regexp.MustCompile(`^(\w+ \w+) bags contain (.+)\.$`)
+	containedPattern = regexp.MustCompile(`(\d+) (\w+ \w+) bags?`)
+)
+
+type bagCount struct {
+	count int
+	bag   string
+}
+
 func init() {
 	registry.Register("2020D7", ParseInput, PartOne, PartTwo)
 }
 
-func ParseInput(filepath string) []string {
-	content, _ := os.ReadFile(filepath)
-	return strings.Split(string(content), "\n")
-}
-
-func PartOne(data []string) int {
-	reverseGraph := make(map[string][]string)
-	rulePattern := regexp.MustCompile(`^(\w+ \w+) bags contain (.+)\.$`)
-	containedPattern := regexp.MustCompile(`(\d+) (\w+ \w+) bags?`)
+func buildForwardGraph(data []string) map[string][]bagCount {
+	forwardGraph := make(map[string][]bagCount)
 
 	for _, line := range data {
 		matches := rulePattern.FindStringSubmatch(line)
@@ -31,18 +35,38 @@ func PartOne(data []string) int {
 		containedString := matches[2]
 
 		if containedString == "no other bags" {
+			forwardGraph[containerBag] = []bagCount{}
 			continue
 		}
 
 		containedMatches := containedPattern.FindAllStringSubmatch(containedString, -1)
 		for _, match := range containedMatches {
 			if len(match) >= 3 {
+				count, _ := strconv.Atoi(match[1])
 				containedBag := match[2]
-				reverseGraph[containedBag] = append(reverseGraph[containedBag], containerBag)
+				forwardGraph[containerBag] = append(forwardGraph[containerBag], bagCount{count: count, bag: containedBag})
 			}
 		}
 	}
 
+	return forwardGraph
+}
+
+func ParseInput(filepath string) []string {
+	content, _ := os.ReadFile(filepath)
+	return strings.Split(string(content), "\n")
+}
+
+func PartOne(data []string) int {
+	forwardGraph := buildForwardGraph(data)
+	reverseGraph := make(map[string][]string)
+
+	for container, contained := range forwardGraph {
+		for _, child := range contained {
+			reverseGraph[child.bag] = append(reverseGraph[child.bag], container)
+		}
+	}
+
 	visited := make(map[string]bool)
 	queue := reverseGraph["shiny gold"]