aoc24/day15/main.go

package main

import (
	"fmt"
	"strings"

	"git.mstar.dev/mstar/aoc24/util"
)

type Area struct {
	a [][]rune
}

func parseLinesToMap(lines []string) Area {
	out := [][]rune{}

	for _, line := range lines {
		out = append(out, []rune(strings.TrimSpace(line)))
	}

	return Area{out}
}

func parseInput(in []byte) (Area, []rune) {
	tmp := strings.Split(string(in), "\n\n")
	return parseLinesToMap(strings.Split(tmp[0], "\n")), []rune(tmp[1])
}

func (area *Area) applyAction(action rune) {
	botX := -1
	botY := -1
outer:
	for iy, line := range area.a {
		for ix, char := range line {
			if char == '@' {
				botX = ix
				botY = iy
				break outer
			}
		}
	}
	area.move(util.Vec2{X: int64(botX), Y: int64(botY)}, action)
}

func (area *Area) move(from util.Vec2, action rune) bool {
	switch action {
	case '<':
		return area.moveLeft(from)
	case '>':
		return area.moveRight(from)
	case 'v':
		return area.moveDown(from)
	case '^':
		return area.moveUp(from)
	default:
		return false
	}
}

func (area *Area) moveLeft(from util.Vec2) bool {
	target := area.a[from.Y][from.X-1]
	switch target {
	case '#':
		return false
	case '.':
		area.a[from.Y][from.X-1] = area.a[from.Y][from.X]
		area.a[from.Y][from.X] = '.'
		return true
	default:
		return area.moveLeft(from.Add(util.Vec2{X: -1, Y: 0})) && area.moveLeft(from)
	}
}

func (area *Area) moveRight(from util.Vec2) bool {
	target := area.a[from.Y][from.X+1]
	switch target {
	case '#':
		return false
	case '.':
		area.a[from.Y][from.X+1] = area.a[from.Y][from.X]
		area.a[from.Y][from.X] = '.'
		return true
	default:
		return area.moveRight(from.Add(util.Vec2{X: 1, Y: 0})) && area.moveRight(from)
	}
}

func (area *Area) canMoveUp(at util.Vec2) bool {
	// fmt.Println("Checking at", at)
	if area.a[at.Y][at.X] == '#' {
		return false
	}
	switch area.a[at.Y-1][at.X] {
	case '#':
		return false
	case '.':
		return true
	case 'O':
		return area.canMoveUp(at.Add(util.Vec2{X: 0, Y: -1}))
	case '[':
		return area.canMoveUp(at.Add(util.Vec2{X: 0, Y: -1})) &&
			area.canMoveUp(at.Add(util.Vec2{X: 1, Y: -1}))
	case ']':
		return area.canMoveUp(at.Add(util.Vec2{X: 0, Y: -1})) &&
			area.canMoveUp(at.Add(util.Vec2{X: -1, Y: -1}))
	default:
		return false
	}
}

func (area *Area) canMoveDown(at util.Vec2) bool {
	if area.a[at.Y][at.X] == '#' {
		return false
	}
	switch area.a[at.Y+1][at.X] {
	case '#':
		return false
	case '.':
		return true
	case 'O':
		return area.canMoveDown(at.Add(util.Vec2{X: 0, Y: 1}))
	case '[':
		return area.canMoveDown(at.Add(util.Vec2{X: 0, Y: 1})) &&
			area.canMoveDown(at.Add(util.Vec2{X: 1, Y: 1}))
	case ']':
		return area.canMoveDown(at.Add(util.Vec2{X: 0, Y: 1})) &&
			area.canMoveDown(at.Add(util.Vec2{X: -1, Y: 1}))
	default:
		return false
	}
}

func (area *Area) moveUp(from util.Vec2) bool {
	// fmt.Printf("Moving up at %v (%s)\n", from, string(area.a[from.Y][from.X]))
	target := area.a[from.Y-1][from.X]
	switch target {
	case '#':
		// fmt.Println("Hit Wall")
		return false
	case '.':
		// fmt.Printf("Empty, moving from %v to %v\n", from, from.Add(util.Vec2{X: 0, Y: -1}))
		area.a[from.Y-1][from.X] = area.a[from.Y][from.X]
		area.a[from.Y][from.X] = '.'
		return true
	case '[':
		if !(area.canMoveUp(from.Add(util.Vec2{X: 0, Y: -1})) &&
			area.canMoveUp(from.Add(util.Vec2{X: 1, Y: -1}))) {
			return false
		}
		// fmt.Println("Moving Box left first")
		return area.moveUp(from.Add(util.Vec2{X: 0, Y: -1})) &&
			area.moveUp(from.Add(util.Vec2{X: 1, Y: -1})) &&
			area.moveUp(from)
	case ']':
		// fmt.Println("Box right")
		return area.canMoveUp(from.Add(util.Vec2{X: 0, Y: -1})) &&
			area.canMoveUp(from.Add(util.Vec2{X: -1, Y: -1})) &&
			area.moveUp(from.Add(util.Vec2{X: 0, Y: -1})) &&
			area.moveUp(from.Add(util.Vec2{X: -1, Y: -1})) &&
			area.moveUp(from)
	case '@':
		// fmt.Println("Moving bot")
		return area.moveUp(from.Add(util.Vec2{X: 0, Y: -1})) && area.moveUp(from)
	case 'O':
		return area.moveUp(from.Add(util.Vec2{X: 0, Y: -1})) && area.moveUp(from)
	default:
		return area.moveUp(from.Add(util.Vec2{X: 0, Y: -1})) && area.moveUp(from)
	}
}

func (area *Area) moveDown(from util.Vec2) bool {
	// fmt.Printf("Moving down at %v\n", from)
	target := area.a[from.Y+1][from.X]
	switch target {
	case '#':
		return false
	case '.':
		area.a[from.Y+1][from.X] = area.a[from.Y][from.X]
		area.a[from.Y][from.X] = '.'
		return true
	case '[':
		return area.canMoveDown(from.Add(util.Vec2{X: 0, Y: 1})) &&
			area.canMoveDown(from.Add(util.Vec2{X: 1, Y: 1})) &&
			area.moveDown(from.Add(util.Vec2{X: 0, Y: 1})) &&
			area.moveDown(from.Add(util.Vec2{X: 1, Y: 1})) &&
			area.moveDown(from)
	case ']':
		return area.canMoveDown(from.Add(util.Vec2{X: 0, Y: 1})) &&
			area.canMoveDown(from.Add(util.Vec2{X: -1, Y: 1})) &&
			area.moveDown(from.Add(util.Vec2{X: 0, Y: 1})) &&
			area.moveDown(from.Add(util.Vec2{X: -1, Y: 1})) &&
			area.moveDown(from)
	default:
		return area.moveDown(from.Add(util.Vec2{X: 0, Y: 1})) && area.moveDown(from)
	}
}

func (area *Area) visualise() string {
	builder := strings.Builder{}
	for _, line := range area.a {
		builder.WriteString(string(line))
		builder.WriteRune('\n')
	}

	return builder.String()
}

func (area *Area) calcPosScore() int {
	score := 0
	for iy, line := range area.a {
		for ix, char := range line {
			if char == 'O' || char == '[' {
				score += calcPosVal(ix, iy)
			}
		}
	}
	return score
}

func Widen(in string) string {
	return strings.ReplaceAll(
		strings.ReplaceAll(
			strings.ReplaceAll(strings.ReplaceAll(in, ".", ".."), "@", "@."),
			"#",
			"##",
		),
		"O",
		"[]",
	)
}

func (area *Area) confirmBoxes(step int) {
	for iy, line := range area.a {
		lastWasBoxLeft := false
		for ix, char := range line {
			if lastWasBoxLeft && char != ']' {
				fmt.Println(area.visualise())
				panic(fmt.Sprintf("Broken box right missing at %d %d, step %d", ix, iy, step))
			}
			switch char {
			case '[':
				lastWasBoxLeft = true
			default:
				lastWasBoxLeft = false
			}
		}
	}
}

func calcPosVal(x, y int) int {
	return x + y*100
}

func main() {
	rawInput := util.LoadFileFromArgs()
	area, inputs := parseInput(rawInput)
	// fmt.Println(area.visualise())
	for _, action := range inputs {
		// fmt.Println(string(action))
		area.applyAction(action)
		// fmt.Println(area.visualise())
	}
	fmt.Printf("Task 1: %d\n", area.calcPosScore())

	wArea, _ := parseInput([]byte(Widen(string(rawInput))))
	fmt.Println(wArea.visualise())
	for i, action := range inputs {
		fmt.Println(string(action))
		wArea.applyAction(action)
		// if i == 806 {
		// fmt.Println(wArea.visualise())
		// }
		wArea.confirmBoxes(i)
		fmt.Println(wArea.visualise())
	}
	fmt.Println(wArea.visualise())
	fmt.Printf("Task 2: %d\n", wArea.calcPosScore())
}