day 7 part 1

main.go

@@ -24,6 +24,9 @@ func main() {
 
 	runAndBenchmark("06", "1", false, solutions.Day06Part01)
 	runAndBenchmark("06", "2", false, solutions.Day06Part02)
+
+	runAndBenchmark("07", "1", false, solutions.Day07Part01)
+	runAndBenchmark("07", "2", true, solutions.Day07Part02)
 }
 
 type execute func(bool) int

solutions/day07.go

@@ -0,0 +1,108 @@
+package solutions
+
+import (
+	"strconv"
+	"strings"
+)
+
+type Bag struct {
+	color             string
+	contents          []BagContent
+	containsShinyGold bool
+}
+
+type BagContent struct {
+	count int
+	color string
+}
+
+// Given a bag statement string, returns its contents
+func parseBagStatement(bagStatement string) Bag {
+	bagEndIndex := strings.Index(bagStatement, " bags contain ")
+	bagColor := bagStatement[:bagEndIndex]
+	bagContentsStr := bagStatement[bagEndIndex+14:]
+
+	// if no aditional bags
+	if bagContentsStr[:2] == "no" {
+		return Bag{color: bagColor, contents: make([]BagContent, 0)}
+	}
+
+	// parse remainder bags
+	bagsContained := strings.Split(bagContentsStr, ", ")
+	bagContents := make([]BagContent, len(bagsContained))
+
+	for idx, bag := range bagsContained {
+		bagCount, err := strconv.Atoi(bag[:1])
+		if err != nil {
+			panic("expected a number, got `" + bag + "`")
+		}
+
+		bagStrIndex := strings.Index(bag, " bag")
+		bagColor2 := bag[2:bagStrIndex]
+
+		bagContents[idx] = BagContent{count: bagCount, color: bagColor2}
+	}
+
+	/*
+		grammar for bag statements:
+
+		statement = bag color, "bags contain", (bag list | empty bag), "."
+		empty bag = "no other bags"
+		bag list = bag declaration, bag declaration+
+		bag declaration = number, bag color, "bag", "s"?
+		bag color = word, word
+	*/
+
+	return Bag{color: bagColor, contents: bagContents}
+}
+
+func bagContainsShinyGold(bag *Bag, bagMap map[string]Bag) bool {
+	if bag.containsShinyGold {
+		return true
+	}
+
+	// recursively search
+	for _, bagName := range bag.contents {
+		if bagName.color == "shiny gold" {
+			bag.containsShinyGold = true
+			return true
+		}
+
+		nextBag := bagMap[bagName.color]
+
+		if bagContainsShinyGold(&nextBag, bagMap) {
+			bag.containsShinyGold = true
+			return true
+		}
+	}
+
+	return false
+}
+
+func Day07Part01(isTest bool) int {
+	input := ReadInput("07", isTest)
+	groups := strings.Split(input, "\n")
+
+	bags := make(map[string]Bag)
+
+	// parse and collect the bags
+	for _, statement := range groups {
+		parsedBag := parseBagStatement(statement)
+		bags[parsedBag.color] = parsedBag
+	}
+
+	shinyGoldContainers := 0
+
+	// process the bags
+	for _, bag := range bags {
+		if bagContainsShinyGold(&bag, bags) {
+			shinyGoldContainers += 1
+		}
+	}
+
+	return shinyGoldContainers
+}
+
+func Day07Part02(isTest bool) int {
+	return -1
+}