[2024] Solution for Day 9

Author: kfarnung

2024/day09/main.go

@@ -0,0 +1,146 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"slices"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+)
+
+type file struct {
+	id   int64
+	size int
+	free int
+}
+
+func part1(input string) int64 {
+	layout := parseInput(input)
+
+	left := 0
+	right := len(layout) - 1
+	for {
+		if left >= right {
+			break
+		} else if layout[left] != -1 {
+			left++
+		} else if layout[right] == -1 {
+			right--
+		} else {
+			layout[left] = layout[right]
+			layout[right] = -1
+		}
+	}
+
+	sum := int64(0)
+	for i, id := range layout {
+		if id == -1 {
+			break
+		}
+
+		sum += int64(id * i)
+	}
+
+	return sum
+}
+
+func part2(input string) int64 {
+	layout := parseInput2(input)
+
+	for i := len(layout) - 1; i >= 0; {
+		didMove := false
+		for j := 0; j < i; j++ {
+			if layout[j].free >= layout[i].size {
+				toMove := layout[i]
+				layout[i-1].free += toMove.size + toMove.free
+				layout = slices.Delete(layout, i, i+1)
+
+				toMove.free = layout[j].free - toMove.size
+				layout[j].free = 0
+				layout = slices.Insert(layout, j+1, toMove)
+				didMove = true
+				break
+			}
+		}
+
+		if !didMove {
+			i--
+		}
+	}
+
+	block := int64(0)
+	sum := int64(0)
+	for _, file := range layout {
+		for i := 0; i < file.size; i++ {
+			sum += int64(block * file.id)
+			block++
+		}
+
+		block += int64(file.free)
+	}
+
+	return sum
+}
+
+func parseInput(input string) []int {
+	var layout []int
+	for _, line := range lib.SplitLines(input) {
+		if len(line) == 0 {
+			continue
+		}
+
+		for i := 0; i < len(line); i += 2 {
+			id := i / 2
+			size := int(line[i] - '0')
+
+			for j := 0; j < size; j++ {
+				layout = append(layout, id)
+			}
+
+			if i+1 < len(line) {
+				free := int(line[i+1] - '0')
+				for j := 0; j < free; j++ {
+					layout = append(layout, -1)
+				}
+			}
+		}
+	}
+
+	return layout
+}
+
+func parseInput2(input string) []file {
+	var files []file
+	for _, line := range lib.SplitLines(input) {
+		if len(line) == 0 {
+			continue
+		}
+
+		for i := 0; i < len(line); i += 2 {
+			file := file{
+				id:   int64(i / 2),
+				size: int(line[i] - '0'),
+			}
+
+			if i+1 < len(line) {
+				file.free = int(line[i+1] - '0')
+			}
+
+			files = append(files, file)
+		}
+	}
+
+	return files
+}
+
+func main() {
+	name := os.Args[1]
+	content, err := lib.LoadFileContent(name)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("Part 1: %d\n", part1(content))
+	fmt.Printf("Part 2: %d\n", part2(content))
+}

2024/day09/main_test.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+	"github.com/stretchr/testify/assert"
+)
+
+var input = strings.Join([]string{
+	"2333133121414131402",
+	"",
+}, "\n")
+
+func TestPart1(t *testing.T) {
+	assert.Equal(t, int64(1928), part1(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(6200294120911), part1(inputContent))
+}
+
+func TestPart2(t *testing.T) {
+	assert.Equal(t, int64(2858), part2(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(6227018762750), part2(inputContent))
+}