advent2022/solutions/day24/day24.go

package day24

import (
	"bufio"
	"fmt"
	"os"
)

type Direction int

const (
	Up Direction = iota
	Down
	Left
	Right
	Stay
)

type Point struct {
	x int
	y int
}

type Directions []Direction

func listContains(dirs Directions, x Direction) bool {
	for _, v := range dirs {
		if x == v {
			return true
		}
	}
	return false
}

func sameBoard(board1 map[Point]Directions, board2 map[Point]Directions) bool {
	if len(board1) != len(board2) {
		return false
	}

	for point, vals1 := range board1 {
		vals2 := board2[point]

		if len(vals1) != len(vals2) {
			return false
		}

		for _, v := range vals1 {
			if !listContains(vals2, v) {
				return false
			}
		}
	}

	return true
}

type Map struct {
	minute   int
	width    int
	height   int
	elf      Point
	entrance Point
	target   Point
}

var boardStates []map[Point]Directions

func printState(state Map) {
	board := boardStates[state.minute%len(boardStates)]

	for y := 0; y < state.height; y++ {
		for x := 0; x < state.width; x++ {
			if x == state.elf.x && y == state.elf.y {
				fmt.Printf("E")
			} else if x == state.target.x && y == state.target.y {
				fmt.Printf(".")
			} else if x == state.entrance.x && y == state.entrance.y {
				fmt.Printf(".")
			} else if y == 0 {
				fmt.Printf("#")
			} else if y == state.height-1 {
				fmt.Printf("#")
			} else if x == 0 || x == state.width-1 {
				fmt.Printf("#")
			} else {
				dir, exists := board[Point{x, y}]
				if exists && len(dir) == 1 {
					switch dir[0] {
					case Left:
						fmt.Printf("<")
					case Right:
						fmt.Printf(">")
					case Up:
						fmt.Printf("^")
					case Down:
						fmt.Printf("v")
					default:
						fmt.Printf("?")
					}
				} else if exists {
					fmt.Printf("%d", len(dir))
				} else {
					fmt.Printf(".")
				}
			}
		}
		fmt.Println()
	}
}

func okMove(state Map) bool {
	if state.elf.x == state.target.x && state.elf.y == state.target.y {
		return true
	}

	if state.elf.x <= 0 || state.elf.y <= 0 {
		return false
	}

	if state.elf.x == state.width-1 || state.elf.y == state.height-1 {
		return false
	}

	board := boardStates[state.minute%len(boardStates)]
	_, exists := board[Point{state.elf.x, state.elf.y}]
	return !exists
}

func nextBoard(width int, height int, board map[Point]Directions) map[Point]Directions {
	newBoard := map[Point]Directions{}

	// start with the snow move
	for point, dirs := range board {
		for _, dir := range dirs {
			switch dir {
			case Left:
				newX := point.x - 1
				if newX == 0 {
					newX = width - 2
				}
				newPoint := Point{newX, point.y}
				newBoard[newPoint] = append(newBoard[newPoint], Left)

			case Right:
				newX := point.x + 1
				if newX == width-1 {
					newX = 1
				}
				newPoint := Point{newX, point.y}
				newBoard[newPoint] = append(newBoard[newPoint], Right)

			case Up:
				newY := point.y - 1
				if newY == 0 {
					newY = height - 2
				}
				newPoint := Point{point.x, newY}
				newBoard[newPoint] = append(newBoard[newPoint], Up)

			case Down:
				newY := point.y + 1
				if newY == height-1 {
					newY = 1
				}
				newPoint := Point{point.x, newY}
				newBoard[newPoint] = append(newBoard[newPoint], Down)
			}
		}
	}

	return newBoard
}

func nextStates(state Map) []Map {
	retval := []Map{}
	newMinute := state.minute + 1

	stay := Map{newMinute, state.width, state.height, state.elf, state.entrance, state.target}
	if okMove(stay) {
		retval = append(retval, stay)
	}

	left := Map{newMinute, state.width, state.height, Point{state.elf.x - 1, state.elf.y}, state.entrance, state.target}
	if okMove(left) {
		retval = append(retval, left)
	}

	right := Map{newMinute, state.width, state.height, Point{state.elf.x + 1, state.elf.y}, state.entrance, state.target}
	if okMove(right) {
		retval = append(retval, right)
	}

	up := Map{newMinute, state.width, state.height, Point{state.elf.x, state.elf.y - 1}, state.entrance, state.target}
	if okMove(up) {
		retval = append(retval, up)
	}

	down := Map{newMinute, state.width, state.height, Point{state.elf.x, state.elf.y + 1}, state.entrance, state.target}
	if okMove(down) {
		retval = append(retval, down)
	}

	return retval
}

func search(initialState Map) int {
	queue := []Map{initialState}
	minute := -1

	for len(queue) > 0 {
		workState := queue[0]

		if workState.minute > minute {
			minute = workState.minute
			filteredStates := []Map{}
			pointsFound := map[Point]bool{}

			for _, state := range queue {
				if state.minute != minute {
					fmt.Println("PANIC: WEIRD")
				}
				_, exists := pointsFound[state.elf]
				if !exists {
					filteredStates = append(filteredStates, state)
					pointsFound[state.elf] = true
				}
			}

			queue = filteredStates
			continue
		}

		if workState.elf.x == workState.target.x && workState.elf.y == workState.target.y {
			return workState.minute
		}

		queue = append(queue[1:], nextStates(workState)...)
	}

	return -1
}

func Run(filename string) {
	file, err := os.Open(filename)
	if err != nil {
		fmt.Println("Error opening file:", err)
		return
	}

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)
	var entrance, exit Point
	board := map[Point]Directions{}
	width := 0
	y := 0

	for scanner.Scan() {
		line := []rune(scanner.Text())

		if line[3] == '#' {
			for x, r := range line {
				if r == '.' {
					if y == 0 {
						entrance = Point{x, 0}
					} else {
						exit = Point{x, y}
					}
				}
			}
		} else {
			for x, r := range line {
				switch r {
				case '>':
					board[Point{x, y}] = Directions{Right}
				case '<':
					board[Point{x, y}] = Directions{Left}
				case '^':
					board[Point{x, y}] = Directions{Up}
				case 'v':
					board[Point{x, y}] = Directions{Down}
				case '.', '#':
					continue
				default:
					fmt.Println("PANIC: Unexpected character", string(r))
				}
			}
		}
		if width == 0 {
			width = len(line)
		}
		y += 1
	}
	file.Close()

	boardStates = []map[Point]Directions{board}
	for {
		nextBoard := nextBoard(width, y, boardStates[len(boardStates)-1])
		if sameBoard(nextBoard, boardStates[0]) {
			break
		}
		boardStates = append(boardStates, nextBoard)
	}
	fmt.Println("Pre-computed", len(boardStates), "boards.")

	initialState := Map{0, width, y, entrance, entrance, exit}
	printState(initialState)
	foundExit := search(initialState)
	fmt.Println("Found exit after", foundExit, "minutes")
	backToEntrance := search(Map{foundExit, initialState.width, initialState.height, initialState.target, initialState.entrance, initialState.entrance})
	fmt.Println("Made it back to the exit at", backToEntrance, "minutes")
	backToExit := search(Map{backToEntrance, initialState.width, initialState.height, initialState.elf, initialState.entrance, initialState.target})
	fmt.Println("And then back to the exit at", backToExit, "minutes")
}