🌅

solutions/day23/day23.go

@@ -0,0 +1,237 @@
+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
+	}
+}