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main.go
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main.go
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package main
import (
"bufio"
"fmt"
"io"
"os"
"path"
"strings"
)
func input() *os.File {
input, err := os.Open(path.Join("2021", "25", "input.txt"))
if err != nil {
panic(err)
}
return input
}
type pos struct {
x, y int
}
const (
indicatorEast = '>'
indicatorSouth = 'v'
indicatorEmpty = '.'
)
type cucumberRegion [][]byte
func (c cucumberRegion) move() bool {
eastMoved := c.moveHerd(indicatorEast, pos{
x: 1,
y: 0,
})
southMoved := c.moveHerd(indicatorSouth, pos{
x: 0,
y: 1,
})
return eastMoved || southMoved
}
func (c cucumberRegion) moveHerd(herdIndicator byte, direction pos) bool {
type move struct {
from, to pos
}
var moves []move
for y := 0; y < len(c); y++ {
for x := 0; x < len(c[y]); x++ {
if c[y][x] != herdIndicator {
continue
}
nextX, nextY := x+direction.x, y+direction.y
if nextX == len(c[y]) {
nextX = 0
}
if nextY == len(c) {
nextY = 0
}
if c[nextY][nextX] == indicatorEmpty {
moves = append(moves, move{
from: pos{x, y},
to: pos{nextX, nextY},
})
}
}
}
for _, mv := range moves {
c[mv.to.y][mv.to.x] = herdIndicator
c[mv.from.y][mv.from.x] = indicatorEmpty
}
return len(moves) != 0
}
func (c cucumberRegion) String() string {
var sb strings.Builder
for _, row := range c {
for _, cucumber := range row {
sb.WriteByte(cucumber)
}
sb.WriteByte('\n')
}
return sb.String()
}
func parse(r io.Reader) cucumberRegion {
var cucumbers cucumberRegion
scanner := bufio.NewScanner(r)
for scanner.Scan() {
line := scanner.Bytes()
row := make([]byte, len(line))
copy(row, line)
cucumbers = append(cucumbers, row)
}
if scanner.Err() != nil {
panic(scanner.Err())
}
return cucumbers
}
func solve(r io.Reader) {
cucumbers := parse(r)
steps := 0
for cucumbers.move() {
steps += 1
}
fmt.Println(steps + 1)
}
func main() {
solve(strings.NewReader("v...>>.vv>\n.vv>>.vv..\n>>.>v>...v\n>>v>>.>.v.\nv>v.vv.v..\n>.>>..v...\n.vv..>.>v.\nv.v..>>v.v\n....v..v.>"))
solve(input())
}