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[2024] Solution for Day 16
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3 files changed

+287
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‎2024/day16/main.go

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package main
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import (
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"fmt"
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"log"
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"math"
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"os"
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"slices"
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"strings"
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"github.com/kfarnung/advent-of-code/2024/lib"
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)
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type point struct {
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x, y int
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}
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type seenKey struct {
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position point
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direction int
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}
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type reindeer struct {
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position point
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direction int
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score int64
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path []point
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}
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func part1(input string) int64 {
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maze, start, _ := parseInput(input)
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queue := []reindeer{{position: start, direction: 90, score: 0}}
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seen := make(map[seenKey]int64)
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for len(queue) > 0 {
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current := queue[0]
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queue = queue[1:]
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key := seenKey{current.position, current.direction}
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if score, ok := seen[key]; ok && current.score >= score {
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continue
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}
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seen[key] = current.score
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if maze[current.position.x][current.position.y] == 'E' {
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return current.score
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}
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straight := getMove(current.position, current.direction)
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if isValid(straight, maze) {
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queue = append(queue, reindeer{
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position: straight,
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direction: current.direction,
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score: current.score + 1})
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}
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left := getMove(current.position, lib.Mod(current.direction-90, 360))
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if isValid(left, maze) {
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queue = append(queue, reindeer{
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position: left,
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direction: lib.Mod(current.direction-90, 360),
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score: current.score + 1001})
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}
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right := getMove(current.position, lib.Mod(current.direction+90, 360))
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if isValid(right, maze) {
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queue = append(queue, reindeer{
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position: right,
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direction: lib.Mod(current.direction+90, 360),
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score: current.score + 1001})
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}
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slices.SortFunc(queue, func(i, j reindeer) int {
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return int(i.score - j.score)
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})
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}
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log.Fatal("No path found")
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return int64(0)
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}
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func part2(input string) int64 {
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maze, start, _ := parseInput(input)
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queue := []reindeer{{position: start, direction: 90, score: 0, path: []point{start}}}
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seen := make(map[seenKey]int64)
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var successPaths [][]point
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var successScore int64 = math.MaxInt64
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for len(queue) > 0 {
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current := queue[0]
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queue = queue[1:]
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if current.score > successScore {
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// We can't get a better score than we already have
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break
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}
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key := seenKey{current.position, current.direction}
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score, ok := seen[key]
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if ok && current.score > score {
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continue
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}
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seen[key] = current.score
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if maze[current.position.x][current.position.y] == 'E' {
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successScore = current.score
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successPaths = append(successPaths, current.path)
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}
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straight := getMove(current.position, current.direction)
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if isValid(straight, maze) {
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queue = append(queue, reindeer{
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position: straight,
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direction: current.direction,
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score: current.score + 1,
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path: duplicatePath(current.path, straight)})
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}
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left := getMove(current.position, lib.Mod(current.direction-90, 360))
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if isValid(left, maze) {
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queue = append(queue, reindeer{
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position: left,
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direction: lib.Mod(current.direction-90, 360),
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score: current.score + 1001,
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path: duplicatePath(current.path, left)})
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}
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right := getMove(current.position, lib.Mod(current.direction+90, 360))
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if isValid(right, maze) {
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queue = append(queue, reindeer{
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position: right,
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direction: lib.Mod(current.direction+90, 360),
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score: current.score + 1001,
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path: duplicatePath(current.path, right)})
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}
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slices.SortFunc(queue, func(i, j reindeer) int {
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return int(i.score - j.score)
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})
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}
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visited := make(map[point]bool)
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for _, path := range successPaths {
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for _, position := range path {
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visited[position] = true
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}
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}
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return int64(len(visited))
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}
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func duplicatePath(path []point, current point) []point {
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duplicate := append([]point(nil), path...)
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duplicate = append(duplicate, current)
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return duplicate
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}
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func getMove(position point, direction int) point {
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switch direction {
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case 0:
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return point{position.x - 1, position.y}
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case 90:
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return point{position.x, position.y + 1}
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case 180:
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return point{position.x + 1, position.y}
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case 270:
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return point{position.x, position.y - 1}
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}
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log.Fatalf("Invalid direction: %d", direction)
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return point{}
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}
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func isValid(position point, maze [][]rune) bool {
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return position.x >= 0 && position.x < len(maze) &&
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position.y >= 0 && position.y < len(maze[position.x]) &&
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maze[position.x][position.y] != '#'
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}
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func parseInput(input string) ([][]rune, point, point) {
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var data [][]rune
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var start, end point
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for i, line := range lib.SplitLines(input) {
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if len(line) == 0 {
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continue
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}
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if startIndex := strings.Index(line, "S"); startIndex != -1 {
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start = point{i, startIndex}
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}
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if endIndex := strings.Index(line, "E"); endIndex != -1 {
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end = point{i, endIndex}
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}
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data = append(data, []rune(line))
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}
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return data, start, end
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}
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func main() {
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name := os.Args[1]
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content, err := lib.LoadFileContent(name)
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if err != nil {
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log.Fatal(err)
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}
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fmt.Printf("Part 1: %d\n", part1(content))
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fmt.Printf("Part 2: %d\n", part2(content))
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}

‎2024/day16/main_test.go

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package main
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import (
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"strings"
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"testing"
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"github.com/kfarnung/advent-of-code/2024/lib"
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"github.com/stretchr/testify/assert"
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)
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var input1 = strings.Join([]string{
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"###############",
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"#.......#....E#",
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"#.#.###.#.###.#",
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"#.....#.#...#.#",
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"#.###.#####.#.#",
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"#.#.#.......#.#",
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"#.#.#####.###.#",
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"#...........#.#",
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"###.#.#####.#.#",
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"#...#.....#.#.#",
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"#.#.#.###.#.#.#",
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"#.....#...#.#.#",
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"#.###.#.#.#.#.#",
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"#S..#.....#...#",
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"###############",
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"",
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}, "\n")
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var input2 = strings.Join([]string{
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"#################",
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"#...#...#...#..E#",
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"#.#.#.#.#.#.#.#.#",
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"#.#.#.#...#...#.#",
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"#.#.#.#.###.#.#.#",
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"#...#.#.#.....#.#",
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"#.#.#.#.#.#####.#",
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"#.#...#.#.#.....#",
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"#.#.#####.#.###.#",
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"#.#.#.......#...#",
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"#.#.###.#####.###",
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"#.#.#...#.....#.#",
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"#.#.#.#####.###.#",
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"#.#.#.........#.#",
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"#.#.#.#########.#",
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"#S#.............#",
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"#################",
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"",
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}, "\n")
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func TestPart1(t *testing.T) {
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assert.Equal(t, int64(7036), part1(input1))
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assert.Equal(t, int64(11048), part1(input2))
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inputContent, err := lib.GetInputContent()
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if err != nil {
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t.Fatal(err)
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}
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assert.Equal(t, int64(102504), part1(inputContent))
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}
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func TestPart2(t *testing.T) {
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assert.Equal(t, int64(45), part2(input1))
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assert.Equal(t, int64(64), part2(input2))
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inputContent, err := lib.GetInputContent()
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if err != nil {
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t.Fatal(err)
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}
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assert.Equal(t, int64(535), part2(inputContent))
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}

‎private

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