day 15

Cargo.toml

@@ -4,7 +4,8 @@ members = [
     "day-*"
 ]
 exclude = [
-    "day-04"
+    "day-04",
+    "day-15"
 ]
 
 [workspace.dependencies]

day-15/day15_test.go

@@ -0,0 +1,23 @@
+package main
+
+import "testing"
+
+var input string = "rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7"
+
+func TestPart1(t *testing.T) {
+	expected := 1320
+	actual := part1(input)
+
+	if actual != expected {
+		t.Errorf("part1 = %d, expected %d", actual, expected)
+	}
+}
+
+func TestPart2(t *testing.T) {
+	expected := 145
+	actual := part2(input)
+
+	if actual != expected {
+		t.Errorf("part2 = %d, expected %d", actual, expected)
+	}
+}

day-15/go.mod

@@ -0,0 +1,3 @@
+module adventofcode/2023/day-15
+
+go 1.21.5

day-15/main.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	data, err := os.ReadFile("./input.txt")
+	if err != nil {
+		panic(err)
+	}
+	input := string(data)
+
+	p1 := part1(input)
+	fmt.Printf("part1: %d\n", p1)
+	p2 := part2(input)
+	fmt.Printf("part2: %d\n", p2)
+}

day-15/part1.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"strings"
+)
+
+func part1(input string) int {
+	parts := strings.Split(input, ",")
+	sum := 0
+	for _, p := range parts {
+		lsum := 0
+		for _, c := range p {
+			lsum += int(c)
+			lsum *= 17
+			lsum %= 256
+		}
+		sum += lsum
+	}
+	return sum
+}

day-15/part2.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"slices"
+	"strconv"
+	"strings"
+)
+
+type lens struct {
+	focal_length int
+	label        string
+}
+
+func part2(input string) int {
+	instructions := strings.Split(input, ",")
+	boxes := make([][]lens, 256)
+	for _, instruction := range instructions {
+		if strings.Contains(instruction, "=") {
+			split := strings.Split(instruction, "=")
+			label := split[0]
+			box_index := hash(label)
+			focal_length, _ := strconv.Atoi(split[1])
+			found_box := boxes[box_index]
+			lens_index := slices.IndexFunc(found_box, func(l lens) bool {
+				return l.label == label
+			})
+			if lens_index >= 0 {
+				found_box[lens_index] = lens{focal_length, label}
+				boxes[box_index] = found_box
+			} else {
+				boxes[box_index] = append(found_box, lens{focal_length, label})
+			}
+		} else if strings.Contains(instruction, "-") {
+			split := strings.Split(instruction, "-")
+			label := split[0]
+			box_index := hash(label)
+			found_box := boxes[box_index]
+			boxes[box_index] = slices.DeleteFunc(found_box, func(l lens) bool {
+				return l.label == label
+			})
+		}
+	}
+
+	sum := 0
+
+	for box_number, box := range boxes {
+		for slot_number, lens := range box {
+			sum += ((box_number + 1) * (slot_number + 1) * lens.focal_length)
+		}
+	}
+
+	return sum
+}
+
+func hash(input string) int {
+	sum := 0
+	for _, c := range input {
+		sum += int(c)
+		sum *= 17
+		sum %= 256
+	}
+	return sum
+}