[2024] Solution for Day 6

kfarnung · kfarnung · commit b5f0a8891c69 · 2024-12-05T21:52:41.000-08:00
diff --git a/2024/day06/main.go b/2024/day06/main.go
@@ -0,0 +1,153 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+)
+
+type position struct {
+	x int
+	y int
+}
+
+func part1(input string) int64 {
+	mappedArea, x, y := parseMap(input)
+	positionMap := getVisitedPositions(mappedArea, x, y)
+
+	return int64(len(positionMap))
+}
+
+func part2(input string) int64 {
+	mappedArea, startX, startY := parseMap(input)
+	positionMap := getVisitedPositions(mappedArea, startX, startY)
+
+	count := int64(0)
+	for position := range positionMap {
+		i, j := position.x, position.y
+		if mappedArea[i][j] != '.' {
+			continue
+		}
+
+		mappedArea[i][j] = '#'
+
+		x, y := startX, startY
+		positionMap := make(map[string]bool)
+		direction := mappedArea[x][y]
+
+		for {
+			if positionMap[fmt.Sprintf("%c,%d,%d", direction, x, y)] {
+				count++
+				break
+			}
+
+			positionMap[fmt.Sprintf("%c,%d,%d", direction, x, y)] = true
+
+			nextX := x
+			nextY := y
+			var nextDirection rune
+
+			switch direction {
+			case '>':
+				nextY++
+				nextDirection = 'v'
+			case '<':
+				nextY--
+				nextDirection = '^'
+			case 'v':
+				nextX++
+				nextDirection = '<'
+			case '^':
+				nextX--
+				nextDirection = '>'
+			default:
+				log.Fatal("Invalid direction")
+			}
+
+			if nextX < 0 || nextY < 0 || nextX >= len(mappedArea) || nextY >= len(mappedArea[nextX]) {
+				break
+			} else if mappedArea[nextX][nextY] == '#' {
+				direction = nextDirection
+			} else {
+				x = nextX
+				y = nextY
+			}
+		}
+
+		mappedArea[i][j] = '.'
+	}
+
+	return count
+}
+
+func getVisitedPositions(mappedArea [][]rune, x, y int) map[position]bool {
+	direction := mappedArea[x][y]
+	positionMap := make(map[position]bool)
+
+	for {
+		positionMap[position{x, y}] = true
+		nextX := x
+		nextY := y
+		var nextDirection rune
+
+		switch direction {
+		case '>':
+			nextY++
+			nextDirection = 'v'
+		case '<':
+			nextY--
+			nextDirection = '^'
+		case 'v':
+			nextX++
+			nextDirection = '<'
+		case '^':
+			nextX--
+			nextDirection = '>'
+		default:
+			log.Fatal("Invalid direction")
+		}
+
+		if nextX < 0 || nextY < 0 || nextX >= len(mappedArea) || nextY >= len(mappedArea[nextX]) {
+			break
+		} else if mappedArea[nextX][nextY] == '#' {
+			direction = nextDirection
+		} else {
+			x = nextX
+			y = nextY
+		}
+	}
+
+	return positionMap
+}
+
+func parseMap(input string) (mappedArea [][]rune, x, y int) {
+	for i, line := range lib.SplitLines(input) {
+		if line == "" {
+			break
+		}
+
+		startingPoint := strings.Index(line, "^")
+		if startingPoint != -1 {
+			x = i
+			y = startingPoint
+		}
+
+		mappedArea = append(mappedArea, []rune(line))
+	}
+
+	return
+}
+
+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))
+}
diff --git a/2024/day06/main_test.go b/2024/day06/main_test.go
@@ -0,0 +1,45 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+	"github.com/stretchr/testify/assert"
+)
+
+var input = strings.Join([]string{
+	"....#.....",
+	".........#",
+	"..........",
+	"..#.......",
+	".......#..",
+	"..........",
+	".#..^.....",
+	"........#.",
+	"#.........",
+	"......#...",
+	"",
+}, "\n")
+
+func TestPart1(t *testing.T) {
+	assert.Equal(t, int64(41), part1(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(5409), part1(inputContent))
+}
+
+func TestPart2(t *testing.T) {
+	assert.Equal(t, int64(6), part2(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(2022), part2(inputContent))
+}
diff --git a/private b/private
@@ -1 +1 @@
-Subproject commit 46d333ab8c3b7037734c44cd2bb8fc07f9bc2593
+Subproject commit b52c706d354aa94edf151399ff1f229c7bd3dc67
