advent2022/solutions/day23/day23.go

package day23

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

type Direction int

const (
	North Direction = iota
	South
	East
	West
)

type Point struct {
	x int
	y int
}

type ElfLocations map[Point]bool

func extents(locations ElfLocations) (topLeft Point, bottomRight Point) {
	lowestX := 1000000000000000000
	highestX := -1000000000000000000
	lowestY := 1000000000000000000
	highestY := -1000000000000000000

	for location := range locations {
		if location.x < lowestX {
			lowestX = location.x
		}

		if location.x > highestX {
			highestX = location.x
		}

		if location.y < lowestY {
			lowestY = location.y
		}

		if location.y > highestY {
			highestY = location.y
		}
	}

	topLeft = Point{lowestX, lowestY}
	bottomRight = Point{highestX, highestY}
	return
}

func hasElf(x int, y int, locations ElfLocations) bool {
	_, exists := locations[Point{x, y}]
	return exists
}

func printMap(locations ElfLocations) {
	topLeft, bottomRight := extents(locations)

	fmt.Println("top left", topLeft)
	fmt.Println("bottom right", bottomRight)
	for y := topLeft.y; y <= bottomRight.y; y++ {
		for x := topLeft.x; x <= bottomRight.x; x++ {
			if hasElf(x, y, locations) {
				fmt.Printf("#")
			} else {
				fmt.Printf(".")
			}
		}
		fmt.Println()
	}
}

func directionIsEmpty(direction Direction, x int, y int, locations ElfLocations) bool {
	switch direction {
	case North:
		return !hasElf(x-1, y-1, locations) && !hasElf(x, y-1, locations) && !hasElf(x+1, y-1, locations)
	case South:
		return !hasElf(x-1, y+1, locations) && !hasElf(x, y+1, locations) && !hasElf(x+1, y+1, locations)
	case West:
		return !hasElf(x-1, y-1, locations) && !hasElf(x-1, y, locations) && !hasElf(x-1, y+1, locations)
	case East:
		return !hasElf(x+1, y-1, locations) && !hasElf(x+1, y, locations) && !hasElf(x+1, y+1, locations)
	}
	return false
}

func showDirection(dir *Direction) string {
	if dir == nil {
		return "<nil>"
	}

	switch *dir {
	case North:
		return "north"
	case South:
		return "south"
	case East:
		return "east"
	case West:
		return "west"
	}

	return "<???>"
}

func proposeMove(x int, y int, directionPreference []Direction, locations ElfLocations) *Point {
	var firstEmpty *Direction = nil
	allEmpty := true

	for _, dir := range directionPreference {
		if directionIsEmpty(dir, x, y, locations) {
			if firstEmpty == nil {
				firstEmpty = new(Direction)
				*firstEmpty = dir
			}
		} else {
			allEmpty = false
		}
	}

	if allEmpty {
		return nil
	}

	if firstEmpty == nil {
		return nil
	}

	switch *firstEmpty {
	case North:
		return &Point{x, y - 1}
	case South:
		return &Point{x, y + 1}
	case East:
		return &Point{x + 1, y}
	case West:
		return &Point{x - 1, y}
	}

	fmt.Println("PANIC: fell through?!")
	return nil
}

func runRound(locations ElfLocations, preferredDirections []Direction) (newLocations ElfLocations, done bool) {
	suggestedMoves := map[Point]Point{}
	takenPoints := map[Point]int{}

	for location := range locations {
		proposed := proposeMove(location.x, location.y, preferredDirections, locations)
		if proposed != nil {
			fmt.Println("Proposed to move", location, "to", proposed)
			suggestedMoves[location] = *proposed
			curVal := takenPoints[*proposed]
			takenPoints[*proposed] = curVal + 1
		}
	}

	newLocations = ElfLocations{}
	done = true
	for originalLocation := range locations {
		newPlace, hasNewPlace := suggestedMoves[originalLocation]
		if hasNewPlace && takenPoints[newPlace] <= 1 {
			newLocations[newPlace] = true
			done = false
		} else {
			newLocations[originalLocation] = true
		}
	}

	return
}

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)
	elfLocations := ElfLocations{}
	y := 0

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

		for x, r := range line {
			if r == '#' {
				elfLocations[Point{x, y}] = true
			}
		}
		y += 1
	}
	file.Close()

	preferredDirections := []Direction{North, South, West, East}
	for i := 0; i < 10; i++ {
		fmt.Println("Round", i)
		printMap(elfLocations)
		newLocations, done := runRound(elfLocations, preferredDirections)
		preferredDirections = append(preferredDirections[1:], preferredDirections[0])
		if done {
			fmt.Println("No one moves after this round, so we're done.")
			break
		}
		elfLocations = newLocations
	}
	printMap(elfLocations)

	topLeft, bottomRight := extents(elfLocations)
	emptyGround := 0
	for x := topLeft.x; x <= bottomRight.x; x++ {
		for y := topLeft.y; y <= bottomRight.y; y++ {
			if !hasElf(x, y, elfLocations) {
				emptyGround += 1
			}
		}
	}
	fmt.Println(emptyGround, "empty spots in smallest bounding box.")

	round := 11
	for {
		fmt.Println("Starting round", round)
		newLocations, done := runRound(elfLocations, preferredDirections)
		if done {
			fmt.Println("No one moved after round", round)
			break
		}
		elfLocations = newLocations
		preferredDirections = append(preferredDirections[1:], preferredDirections[0])
		round += 1
	}
}