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package main
import (
"bufio"
"fmt"
"math"
"os"
"slices"
"strings"
)
func main() {
fmt.Println(part1(readData("example.txt")))
fmt.Println(1358)
fmt.Println(part1(readData("data.txt")))
}
func IntAbs(x int) int {
if x >= 0 {
return x
} else {
return -x
}
}
func part1(maze [][]byte) (score1, score2 int) {
startX, startY := findInMaze(maze, 'S')
endX, endY := findInMaze(maze, 'E')
distMap := buildDistMap(maze, startX, startY, endX, endY)
dirs := [][2]int{}
for dy := -20; dy <= 20; dy++ {
for dx := -20; dx <= 20; dx++ {
d := IntAbs(dx) + IntAbs(dy)
if d >= 1 && d <= 20 {
dirs = append(dirs, [2]int{dx, dy})
}
}
}
x, y := startX, startY
for x != endX || y != endY {
distNow := distMap[y][x]
xNext, yNext := x, y
for _, dir := range dirs {
x2, y2 := x+dir[0], y+dir[1]
dist := IntAbs(dir[0]) + IntAbs(dir[1])
if dist == 1 && maze[y2][x2] != '#' && distMap[y2][x2] > distNow {
xNext, yNext = x2, y2
}
if dist > 1 && x2 >= 0 && y2 >= 0 && y2 < len(maze) && x2 < len(maze[y2]) && distMap[y2][x2] > distNow && maze[y2][x2] != '#' {
saved := distMap[y2][x2] - distNow - dist
if dist == 2 && saved >= 100 {
score1++
}
if saved >= 100 {
score2++
}
}
}
x, y = xNext, yNext
}
return
}
func buildDistMap(maze [][]byte, x, y int, endX, endY int) (distMap [][]int) {
distMap = make([][]int, len(maze))
for y, _ := range distMap {
distMap[y] = make([]int, len(maze[0]))
for x := range distMap[y] {
distMap[y][x] = math.MaxInt
}
}
distMap[y][x] = 0
var dirs = [4][2]int{{1, 0}, {-1, 0}, {0, 1}, {0, -1}}
for x != endX || y != endY {
for _, dir := range dirs {
x2, y2 := x+dir[0], y+dir[1]
if maze[y2][x2] != '#' && distMap[y2][x2] == math.MaxInt {
distMap[y2][x2] = distMap[y][x] + 1
x, y = x2, y2
break
}
}
}
return
}
func findInMaze(maze [][]byte, needle byte) (x, y int) {
for y, line := range maze {
if x := slices.Index(line, needle); x >= 0 {
return x, y
}
}
panic("not found")
}
func readData(fileName string) (maze [][]byte) {
fp, _ := os.Open(fileName)
scanner := bufio.NewScanner(fp)
for scanner.Scan() {
maze = append(maze, []byte(strings.TrimSpace(scanner.Text())))
}
return
}
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