/
main.go
174 lines (158 loc) · 2.63 KB
/
main.go
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package main
import (
"bytes"
"fmt"
"hash/crc32"
"os"
"github.com/samber/lo"
)
func parse() [][]byte {
input := lo.Must(os.ReadFile("./input"))
grid := bytes.Split(input, []byte{'\n'})
if len(grid[len(grid)-1]) == 0 {
grid = grid[:len(grid)-1]
}
return grid
}
func tilt(grid [][]byte, dir byte) {
m := len(grid)
n := len(grid[0])
var (
nflag int
initFlag int
vertical bool
is, ie, io int
js, je, jo int
)
switch dir {
case 'N':
nflag = n
initFlag = -1
vertical = true
is, ie, io = 0, m, 1
js, je, jo = 0, n, 1
case 'W':
nflag = m
initFlag = -1
vertical = false
is, ie, io = 0, n, 1
js, je, jo = 0, m, 1
case 'S':
nflag = n
initFlag = m
vertical = true
is, ie, io = m-1, -1, -1
js, je, jo = 0, n, 1
case 'E':
nflag = m
initFlag = n
vertical = false
is, ie, io = n-1, -1, -1
js, je, jo = 0, m, 1
}
flags := make([]int, nflag)
for i := range flags {
flags[i] = initFlag
}
for i := is; i != ie; i += io {
for j := js; j != je; j += jo {
var c byte
if vertical {
c = grid[i][j]
} else {
c = grid[j][i]
}
switch c {
case '.':
continue
case '#':
flags[j] = i
default:
if vertical {
if io == 1 {
if i-flags[j] > 1 {
flags[j]++
grid[i][j] = '.'
grid[flags[j]][j] = 'O'
} else {
flags[j] = i
}
} else {
if flags[j]-i > 1 {
flags[j]--
grid[i][j] = '.'
grid[flags[j]][j] = 'O'
} else {
flags[j] = i
}
}
} else {
if io == 1 {
if i-flags[j] > 1 {
flags[j]++
grid[j][i] = '.'
grid[j][flags[j]] = 'O'
} else {
flags[j] = i
}
} else {
if flags[j]-i > 1 {
flags[j]--
grid[j][i] = '.'
grid[j][flags[j]] = 'O'
} else {
flags[j] = i
}
}
}
}
}
}
}
func cycle(grid [][]byte) {
tilt(grid, 'N')
tilt(grid, 'W')
tilt(grid, 'S')
tilt(grid, 'E')
}
// unsafe
func hash(grid [][]byte) uint32 {
b := make([]byte, 0, len(grid)*len(grid[0]))
for _, r := range grid {
b = append(b, r...)
}
return crc32.ChecksumIEEE(b)
}
func main() {
grid := parse()
m := len(grid)
n := len(grid[0])
cached := make(map[uint32]int)
var cur int
target := 1000000000
cached[hash(grid)] = 0
for {
cycle(grid)
cur++
h := hash(grid)
pre, ok := cached[h]
if ok {
period := cur - pre
cur = cur + period*((target-cur)/period)
} else {
cached[h] = cur
}
if cur == target {
break
}
}
var sum int
for j := 0; j < n; j++ {
for i := 0; i < m; i++ {
if grid[i][j] == 'O' {
sum += m - i
}
}
}
fmt.Println(sum)
}