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package main
import (
"fmt"
"os"
"slices"
"strings"
)
type Orientation = int
const (
Up Orientation = 0
Right Orientation = 1
Down Orientation = 2
Left Orientation = 3
)
func FileRead(path string) string {
file, err := os.ReadFile(path)
if err != nil {
fmt.Println("Couldn't Read file: ", err)
}
return string(file)
}
func turn90(orientation Orientation) Orientation {
orientations := [4]Orientation{Up, Right, Down, Left}
return orientations[(orientation+1)%4]
}
type Grid = []string
func isValid(grid *Grid, x int, y int) bool {
n, m := len(*grid), len((*grid)[0])
return x >= 0 && x < n && y >= 0 && y < m
}
func replaceCharGrid(grid *Grid, x int, y int, ch rune) {
str := (*grid)[x]
runes := []rune(str)
runes[y] = ch
(*grid)[x] = string(runes)
}
func simulateTrail(grid *Grid, gPos [2]int) int {
set := make(map[[2]int]struct{})
set[gPos] = struct{}{}
curOrientation := getOrientation((*grid)[gPos[0]][gPos[1]])
dx := [4]int{-1, 0, 1, 0} // Up, Right, Down, Left
dy := [4]int{0, 1, 0, -1}
for {
nx := gPos[0] + dx[curOrientation]
ny := gPos[1] + dy[curOrientation]
if isValid(grid, nx, ny) {
curPoint := (*grid)[nx][ny]
if !isObstacle(curPoint) {
gPos = [2]int{nx, ny}
replaceCharGrid(grid, nx, ny, 'X')
set[gPos] = struct{}{}
} else {
curOrientation = turn90(curOrientation)
}
} else {
break
}
}
return len(set)
}
func parseInput(data string) Grid {
var grid Grid
for _, line := range strings.Split(data, "\n") {
if len(line) > 0 {
grid = append(grid, line)
}
}
return grid
}
func getOrientation(ch byte) Orientation {
if ch == '^' {
return Up
} else if ch == '>' {
return Right
} else if ch == '<' {
return Left
} else {
return Down
}
}
func isGaurd(ch byte) bool {
return slices.Contains([]string{"^", ">", "<", "V"}, string(ch))
}
func isObstacle(ch byte) bool {
return ch == '#'
}
func solve_part_one(data string) int {
grid := parseInput(data)
var guardPosition [2]int
for i, row := range grid {
for j, ch := range row {
if isGaurd(byte(ch)) {
guardPosition = [2]int{i, j}
}
}
}
trailCount := simulateTrail(&grid, guardPosition)
return trailCount
}
func isStuck(grid *Grid, gPos [2]int) bool {
n, m := len(*grid), len((*grid)[0])
visited := make([]bool, n*m*4)
curOrientation := getOrientation((*grid)[gPos[0]][gPos[1]])
visited[((gPos[0]*n)+gPos[1])*4+curOrientation] = true
dx := [4]int{-1, 0, 1, 0} // Up, Right, Down, Left
dy := [4]int{0, 1, 0, -1}
for {
nx := gPos[0] + dx[curOrientation]
ny := gPos[1] + dy[curOrientation]
if isValid(grid, nx, ny) {
curPoint := (*grid)[nx][ny]
if !isObstacle(curPoint) {
gPos = [2]int{nx, ny}
if visited[((nx*n)+ny)*4+curOrientation] {
return true
}
visited[((nx*n)+ny)*4+curOrientation] = true
} else {
curOrientation = turn90(curOrientation)
}
} else {
break
}
}
return false
}
func solve_part_two(data string) int {
grid := parseInput(data)
var guardPosition [2]int
for i, row := range grid {
for j, ch := range row {
if isGaurd(byte(ch)) {
guardPosition = [2]int{i, j}
}
}
}
n, m := len(grid), len(grid[0])
ans := 0
for i := range n {
for j := range m {
gridCopy := make([]string, len(grid))
copy(gridCopy, grid)
if i != guardPosition[0] || j != guardPosition[1] {
replaceCharGrid(&gridCopy, i, j, '#')
if isStuck(&gridCopy, guardPosition, n*m) {
ans++
}
}
}
}
return ans
}
func main() {
test := FileRead("../input/day6.test")
prod := FileRead("../input/day6.prod")
fmt.Println("Part_1 test: ", solve_part_one(test))
fmt.Println("Part_1 prod: ", solve_part_one(prod))
fmt.Println("Part_2 test: ", solve_part_two(test))
fmt.Println("Part_2 prod: ", solve_part_two(prod))
}
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