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main.go
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main.go
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// -*- compile-command: "go run main.go ../example1.txt ../input.txt"; -*-
package main
import (
"flag"
"fmt"
"log"
"math/bits"
"strings"
. "github.com/gmlewis/advent-of-code-2021/enum"
"github.com/gmlewis/advent-of-code-2021/must"
)
var logf = log.Printf
var printf = fmt.Printf
func main() {
flag.Parse()
Each(flag.Args(), process)
}
func process(filename string) {
logf("Processing %v ...", filename)
lines := must.ReadFileLines(filename)
puz := parsePuzzle(lines)
allPaths := allPathsT{[]keyT{{0, -1}}}
moves := puz.bestPath(allPaths)
printf("Solution: %v\n", len(moves)-1)
}
const (
blizUp blizT = 1 << iota
blizRight
blizDown
blizLeft
)
type keyT [2]int
type blizT byte
type puzT struct {
minutes int
width int
height int
grid map[keyT]blizT
}
type allPathsT [][]keyT
func (p *puzT) bestPath(allPaths allPathsT) []keyT {
for {
p.minutes++
p.blowWindNextStep()
var newPaths allPathsT
alreadySuggested := map[keyT]bool{}
for _, path := range allPaths {
pos := path[0]
options := p.allPossibleMovesFrom(pos)
// log.Printf("Minute %v - pos=%v - %v options for path #%v: %+v", p.minutes, pos, len(options), i+1, options)
for _, option := range options {
if alreadySuggested[option] {
continue
}
alreadySuggested[option] = true
newPath := append([]keyT{option}, path...)
if option[0] == p.width-1 && option[1] == p.height {
// log.Printf("FOUND SOLUTION after %v minutes!", p.minutes)
return newPath
}
newPaths = append(newPaths, newPath)
}
}
allPaths = newPaths
}
return nil
}
func (p *puzT) allPossibleMovesFrom(pos keyT) []keyT {
if pos[0] == p.width-1 && pos[1] == p.height { // already solved - no options
return nil
}
if pos[0] == p.width-1 && pos[1] == p.height-1 { // at exit - one option
return []keyT{{p.width - 1, p.height}}
}
var options []keyT
if p.grid[pos] == 0 { // stay put
options = append(options, pos)
}
f := func(k keyT) {
if p.grid[k] == 0 && k[1] >= 0 && k[1] < p.height && k[0] >= 0 && k[0] < p.width {
options = append(options, k)
}
}
f(keyT{pos[0] + 1, pos[1]})
f(keyT{pos[0], pos[1] + 1})
f(keyT{pos[0] - 1, pos[1]})
f(keyT{pos[0], pos[1] - 1})
return options
}
func (p *puzT) blowWindNextStep() {
g := map[keyT]blizT{}
for k, v := range p.grid {
if v&blizUp == blizUp {
key := keyT{k[0], (k[1] - 1 + p.height) % p.height}
g[key] |= blizUp
}
if v&blizRight == blizRight {
key := keyT{(k[0] + 1) % p.width, k[1]}
g[key] |= blizRight
}
if v&blizDown == blizDown {
key := keyT{k[0], (k[1] + 1) % p.height}
g[key] |= blizDown
}
if v&blizLeft == blizLeft {
key := keyT{(k[0] - 1 + p.width) % p.width, k[1]}
g[key] |= blizLeft
}
}
p.grid = g
}
func parsePuzzle(lines []string) *puzT {
p := &puzT{grid: map[keyT]blizT{}}
ReduceWithIndex(lines, p, parseLine)
return p
}
func parseLine(y int, line string, p *puzT) *puzT {
if line[2] == '#' { // skip line
p.width = len(line) - 2
return p
}
p.height = y
parseRune := func(x int, r rune, p *puzT) *puzT {
if r == '#' {
return p
}
k := keyT{x - 1, y - 1}
switch r {
case '.':
case '^':
p.grid[k] = blizUp
case '>':
p.grid[k] = blizRight
case 'v':
p.grid[k] = blizDown
case '<':
p.grid[k] = blizLeft
default:
log.Fatalf("unknown rune %v", r)
}
return p
}
ReduceWithIndex([]rune(line), p, parseRune)
return p
}
func (p *puzT) String() string {
lines := []string{fmt.Sprintf("#.%v", strings.Repeat("#", p.width-1))}
for y := 0; y < p.height; y++ {
var line string
for x := 0; x < p.width; x++ {
k := keyT{x, y}
v := bits.OnesCount(uint(p.grid[k]))
switch {
case v == 0:
line += "."
case v == 2:
line += "2"
case v == 3:
line += "3"
case v == 4:
line += "4"
case v == 1 && p.grid[k] == blizUp:
line += "^"
case v == 1 && p.grid[k] == blizRight:
line += ">"
case v == 1 && p.grid[k] == blizDown:
line += "v"
case v == 1 && p.grid[k] == blizLeft:
line += "<"
default:
log.Printf("unhandled v=%v, k=%v, grid[k]=%v", v, k, p.grid[k])
}
}
lines = append(lines, line)
}
lines = append(lines, fmt.Sprintf("%v.#", strings.Repeat("#", p.width-1)))
return strings.Join(lines, "#\n#")
}