[2024] Solution for Day 18

Author: kfarnung

2024/day18/main.go

@@ -0,0 +1,126 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+)
+
+type point struct {
+	x, y int
+}
+
+type mazeState struct {
+	position  point
+	stepCount int
+}
+
+func part1(input string, dimension, count int) int64 {
+	points, err := parseInput(input)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	grid := initializeGrid(dimension)
+	corruptGrid(grid, points, count)
+
+	return int64(findShortestPath(grid, point{0, 0}, point{dimension, dimension}))
+}
+
+func part2(input string, dimension int) string {
+	points, err := parseInput(input)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	grid := initializeGrid(dimension)
+
+	for _, p := range points {
+		grid[p.y][p.x] = '#'
+
+		if findShortestPath(grid, point{0, 0}, point{dimension, dimension}) == 0 {
+			return fmt.Sprintf("%d,%d", p.x, p.y)
+		}
+	}
+
+	log.Fatal("No solution found")
+	return ""
+}
+
+func findShortestPath(grid [][]rune, start, end point) int {
+	queue := []mazeState{{start, 0}}
+	steps := make(map[point]int)
+
+	for len(queue) > 0 {
+		current := queue[0]
+		queue = queue[1:]
+
+		if stepCount, ok := steps[current.position]; ok && stepCount <= current.stepCount {
+			continue
+		}
+
+		steps[current.position] = current.stepCount
+
+		if current.position == end {
+			break
+		}
+
+		for _, direction := range []point{{0, 1}, {0, -1}, {1, 0}, {-1, 0}} {
+			next := point{current.position.x + direction.x, current.position.y + direction.y}
+			if next.y >= 0 && next.y < len(grid) && next.x >= 0 && next.x < len(grid[next.y]) && grid[next.y][next.x] == '.' {
+				queue = append(queue, mazeState{next, current.stepCount + 1})
+			}
+		}
+	}
+
+	return steps[end]
+}
+
+func corruptGrid(grid [][]rune, points []point, count int) {
+	for i := 0; i < count; i++ {
+		grid[points[i].y][points[i].x] = '#'
+	}
+}
+
+func initializeGrid(dimension int) [][]rune {
+	grid := make([][]rune, dimension+1)
+	for i := range grid {
+		grid[i] = make([]rune, dimension+1)
+		for j := range grid[i] {
+			grid[i][j] = '.'
+		}
+	}
+
+	return grid
+}
+
+func parseInput(input string) ([]point, error) {
+	var points []point
+	for _, line := range lib.SplitLines(input) {
+		if line == "" {
+			continue
+		}
+
+		var x, y int
+		_, err := fmt.Sscanf(line, "%d,%d", &x, &y)
+		if err != nil {
+			return nil, err
+		}
+		points = append(points, point{x, y})
+	}
+
+	return points, nil
+}
+
+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, 70, 1024))
+	fmt.Printf("Part 2: %s\n", part2(content, 70))
+}

2024/day18/main_test.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+	"github.com/stretchr/testify/assert"
+)
+
+var input = strings.Join([]string{
+	"5,4",
+	"4,2",
+	"4,5",
+	"3,0",
+	"2,1",
+	"6,3",
+	"2,4",
+	"1,5",
+	"0,6",
+	"3,3",
+	"2,6",
+	"5,1",
+	"1,2",
+	"5,5",
+	"2,5",
+	"6,5",
+	"1,4",
+	"0,4",
+	"6,4",
+	"1,1",
+	"6,1",
+	"1,0",
+	"0,5",
+	"1,6",
+	"2,0",
+	"",
+}, "\n")
+
+func TestPart1(t *testing.T) {
+	assert.Equal(t, int64(22), part1(input, 6, 12))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(330), part1(inputContent, 70, 1024))
+}
+
+func TestPart2(t *testing.T) {
+	assert.Equal(t, "6,1", part2(input, 6))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, "10,38", part2(inputContent, 70))
+}