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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"
"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)
}
const totalRounds = 10
func process(filename string) {
logf("Processing %v ...", filename)
lines := must.ReadFileLines(filename)
puz := ReduceWithIndex(lines, &puzT{grid: map[keyT]rune{}}, parseLine)
// log.Printf("puzzle:\n%v", puz)
for i := 0; i < totalRounds; i++ {
var ok bool
if puz, ok = puz.round(i); !ok {
break
}
}
printf("Solution: %v\n", puz.spaces())
}
type keyT [2]int
type puzT struct {
minX int
maxX int
minY int
maxY int
grid map[keyT]rune
}
func (p *puzT) round(roundNum int) (*puzT, bool) {
newP := &puzT{minX: p.maxX, minY: p.maxY, grid: map[keyT]rune{}}
// first pass
wishMove := map[keyT]keyT{} // map[from]to
possibleMoves := map[keyT]keyT{} // map[to]from
for from := range p.grid {
to, ok := p.elfMove(from, roundNum)
if !ok {
continue
}
if f1, ok := possibleMoves[to]; ok {
delete(wishMove, f1)
continue
}
possibleMoves[to] = from
wishMove[from] = to
}
if len(wishMove) == 0 {
return p, false
}
// second pass
for from := range p.grid {
to, ok := wishMove[from]
if !ok {
to = from
}
newP.grid[to] = '#'
if to[0] < newP.minX {
newP.minX = to[0]
}
if to[0] > newP.maxX {
newP.maxX = to[0]
}
if to[1] < newP.minY {
newP.minY = to[1]
}
if to[1] > newP.maxY {
newP.maxY = to[1]
}
}
// log.Printf("newP:\n%v", newP)
return newP, true
}
var (
rounds = [][]keyT{
{keyT{-1, -1}, keyT{0, -1}, keyT{1, -1}}, // NW, N, NE
{keyT{-1, 1}, keyT{0, 1}, keyT{1, 1}}, // SW, S, SE
{keyT{-1, -1}, keyT{-1, 0}, keyT{-1, 1}}, // NW, W, SW
{keyT{1, -1}, keyT{1, 0}, keyT{1, 1}}, // NE, E, SE
}
)
func (p *puzT) elfMove(from keyT, roundNum int) (keyT, bool) {
var shouldMove bool
for dy := -1; dy <= 1; dy++ {
for dx := -1; dx <= 1; dx++ {
if dx == 0 && dy == 0 {
continue
}
if p.grid[keyT{from[0] + dx, from[1] + dy}] == '#' {
shouldMove = true
break
}
}
}
if !shouldMove {
return keyT{}, false
}
for i := 0; i < 4; i++ {
round := rounds[(i+roundNum)%4]
to := keyT{from[0] + round[1][0], from[1] + round[1][1]}
if p.grid[keyT{from[0] + round[0][0], from[1] + round[0][1]}] != '#' &&
p.grid[to] != '#' &&
p.grid[keyT{from[0] + round[2][0], from[1] + round[2][1]}] != '#' {
return to, true
}
}
return keyT{}, false
}
func parseLine(y int, line string, acc *puzT) *puzT {
parseRune := func(x int, r rune, p *puzT) *puzT {
if r == '#' {
p.grid[keyT{x, y}] = r
if x > p.maxX {
p.maxX = x
}
if y > p.maxY {
p.maxY = y
}
}
return p
}
return ReduceWithIndex([]rune(line), acc, parseRune)
}
func (p *puzT) spaces() int {
var spaces int
for y := p.minY; y <= p.maxY; y++ {
for x := p.minX; x <= p.maxX; x++ {
if p.grid[keyT{x, y}] != '#' {
spaces++
}
}
}
return spaces
}
func (p *puzT) String() string {
var lines []string
for y := p.minY; y <= p.maxY; y++ {
var line string
for x := p.minX; x <= p.maxX; x++ {
if p.grid[keyT{x, y}] == '#' {
line += "#"
} else {
line += "."
}
}
lines = append(lines, line)
}
return strings.Join(lines, "\n")
}