2 files changed, 178 insertions, 0 deletions
diff --git a/2023/Go/internal/day_04/part_01/part_01.go b/2023/Go/internal/day_04/part_01/part_01.go
new file mode 100644
index 0000000..1a215b1
--- /dev/null
+++ b/2023/Go/internal/day_04/part_01/part_01.go
@@ -0,0 +1,130 @@
+package part_01
+
+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_01_sample.txt")
+	} else {
+		contents, _ = os.ReadFile("../_input/day_04.txt")
+	}
+
+	lines := strings.Split(string(contents), "\n")
+
+	answer := 0
+	for _, line := range lines {
+		if line == "" || line == "\n" {
+			continue
+		}
+
+		card := parseCardLine(line)
+		score := tallyScore(card)
+
+		answer += score
+	}
+
+	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 tallyScore(card Card) int {
+	score := 0
+	for _, winningNumber := range card.winningNumbers {
+		if slices.Contains(card.haveNumbers, winningNumber) {
+			if score == 0 {
+				score = 1
+			} else {
+				score *= 2
+			}
+		}
+	}
+
+	return score
+}
diff --git a/2023/Go/internal/day_04/part_01/part_01_test.go b/2023/Go/internal/day_04/part_01/part_01_test.go
new file mode 100644
index 0000000..f6f1a83
--- /dev/null
+++ b/2023/Go/internal/day_04/part_01/part_01_test.go
@@ -0,0 +1,48 @@
+package part_01
+
+import (
+	"testing"
+)
+
+func TestParseCardLine(t *testing.T) {
+	input := "Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53"
+	expected := Card{1, []int{41, 48, 83, 86, 17}, []int{83, 86, 6, 31, 17, 9, 48, 53}}
+
+	actual := parseCardLine(input)
+
+	if actual.id != expected.id {
+		t.Errorf("ERROR: ID %d does not match expected %d", actual.id, expected.id)
+	}
+
+	if len(actual.winningNumbers) != len(expected.winningNumbers) {
+		t.Errorf("ERROR: len(WinningNumbers) %d does not match expected %d", len(actual.winningNumbers), len(expected.winningNumbers))
+	}
+
+	if len(actual.haveNumbers) != len(expected.haveNumbers) {
+		t.Errorf("ERROR: len(HaveNumbers) %d does not match expected %d", len(actual.haveNumbers), len(expected.haveNumbers))
+	}
+
+	for i, num := range actual.winningNumbers {
+		if num != expected.winningNumbers[i] {
+			t.Errorf("ERROR: WinningNumber %d does not match expected %d", num, expected.winningNumbers[i])
+		}
+	}
+
+	for i, num := range actual.haveNumbers {
+		if num != expected.haveNumbers[i] {
+			t.Errorf("ERROR: HaveNumber %d does not match expected %d", num, expected.haveNumbers[i])
+		}
+	}
+
+}
+
+func TestTallyScore(t *testing.T) {
+	card := Card{1, []int{41, 48, 83, 86, 17}, []int{83, 86, 6, 31, 17, 9, 48, 53}}
+	expected := 8
+
+	actual := tallyScore(card)
+
+	if actual != expected {
+		t.Errorf("ERROR: Score %d does not match expected %d", actual, expected)
+	}
+}