1 files changed, 142 insertions, 0 deletions
diff --git a/2023/go/internal/day_04/part_02/part_02.go b/2023/go/internal/day_04/part_02/part_02.go
new file mode 100644
index 0000000..a9e3152
--- /dev/null
+++ b/2023/go/internal/day_04/part_02/part_02.go
@@ -0,0 +1,142 @@
+package part_02
+
+import (
+	"os"
+	"slices"
+	"strconv"
+	"strings"
+)
+
+const USE_SAMPLE = false
+
+type UnparsedCard struct {
+	id             string
+	winningNumbers []string
+	haveNumbers    []string
+}
+
+type Card struct {
+	id             int
+	winningNumbers []int
+	haveNumbers    []int
+}
+
+func (c UnparsedCard) parse() Card {
+	var card Card
+
+	id, err := strconv.Atoi(c.id)
+	if err != nil {
+		panic(err)
+	}
+	card.id = id
+
+	for _, number := range c.winningNumbers {
+		num, err := strconv.Atoi(number)
+		if err != nil {
+			panic(err)
+		}
+		card.winningNumbers = append(card.winningNumbers, num)
+	}
+
+	for _, number := range c.haveNumbers {
+		num, err := strconv.Atoi(number)
+		if err != nil {
+			panic(err)
+		}
+		card.haveNumbers = append(card.haveNumbers, num)
+	}
+
+	return card
+}
+
+func Solve() {
+	var contents []byte
+	if USE_SAMPLE {
+		contents, _ = os.ReadFile("../_input/day_04_part_02_sample.txt")
+	} else {
+		contents, _ = os.ReadFile("../_input/day_04.txt")
+	}
+
+	lines := strings.Split(string(contents), "\n")
+
+	dict := map[int]Card{}
+	var cards []Card
+	for _, line := range lines {
+		if line == "" || line == "\n" {
+			continue
+		}
+
+		card := parseCardLine(line)
+
+		dict[card.id] = card
+		cards = append(cards, card)
+	}
+
+	answer := processCards(dict, cards)
+
+	println(answer)
+}
+
+// "Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53"
+func parseCardLine(line string) Card {
+	var unparsedCard UnparsedCard
+
+	filteredLine := strings.ReplaceAll(line, "\r", "")
+
+	// "Card 1"
+	card_parts := strings.Split(filteredLine, ":")[0]
+	id_parts := strings.Split(card_parts, " ")
+	id := id_parts[len(id_parts)-1]
+	unparsedCard.id = strings.ReplaceAll(id, " ", "")
+
+	// "41 48 83 86 17 | 83 86  6 31 17  9 48 53"
+	numbers := strings.Split(filteredLine, ":")[1]
+
+	// " 41 48 83 86 17"
+	winningNumberString := strings.Split(numbers, "|")[0]
+	// ["", "41", "48", "83", "86", "17"]
+	winningNumbers := strings.Split(winningNumberString, " ")
+	for _, num := range winningNumbers {
+		if num == "" || num == " " {
+			continue
+		}
+		unparsedCard.winningNumbers = append(unparsedCard.winningNumbers, num)
+	}
+
+	// " 83 86  6 31 17  9 48 53"
+	haveNumberString := strings.Split(numbers, "|")[1]
+	// ["", "83", "86", "", "6", "31", "17", "", "9", "48", "53"]
+	haveNumbers := strings.Split(haveNumberString, " ")
+	for _, num := range haveNumbers {
+		if num == "" || num == " " {
+			continue
+		}
+		unparsedCard.haveNumbers = append(unparsedCard.haveNumbers, num)
+	}
+
+	return unparsedCard.parse()
+}
+
+func processCards(dict map[int]Card, cards []Card) int {
+	for i := 0; i < len(cards); i++ {
+		card := cards[i]
+		matchCount := calculateNumberOfMatches(card)
+		for j := card.id + 1; j < (card.id + 1 + matchCount); j++ {
+			copyCard := dict[j]
+			cards = append(cards, copyCard)
+		}
+	}
+
+	return len(cards)
+}
+
+func calculateNumberOfMatches(card Card) int {
+	matchCount := 0
+	for _, winningNumber := range card.winningNumbers {
+		if slices.Contains(card.haveNumbers, winningNumber) {
+			matchCount++
+		}
+	}
+
+	return matchCount
+}