Almost

16/code.go

@@ -28,6 +28,146 @@ func readInput(file *os.File) [][]byte {
 	return board
 }
 
+const (
+	Horizontal = '-'
+	Vertical   = '|'
+	Slash      = '/'
+	Backslash  = '\\'
+	Empty      = '.'
+	Mark       = '#'
+)
+
+const (
+	North = iota
+	South
+	East
+	West
+)
+
+type Beam struct {
+	y, x      int
+	direction int
+}
+
+func (b *Beam) canContinue(board [][]byte, height int, width int) []Beam {
+	var beams []Beam
+	if b.x < 0 || b.x >= width || b.y < 0 || b.y >= height {
+		return beams
+	}
+
+	switch board[b.y][b.x] {
+	case Horizontal:
+		if b.direction != East && b.direction != West {
+			b.direction = East
+			beams = append(beams, *b)
+			b.direction = West
+			beams = append(beams, *b)
+
+			return beams
+		}
+	case Vertical:
+		if b.direction != South && b.direction != North {
+			b.direction = South
+			beams = append(beams, *b)
+			b.direction = North
+			beams = append(beams, *b)
+
+			return beams
+		}
+	case Slash:
+		switch b.direction {
+		case North:
+			b.direction = East
+		case South:
+			b.direction = West
+		case East:
+			b.direction = North
+		case West:
+			b.direction = South
+		}
+	case Backslash:
+		switch b.direction {
+		case North:
+			b.direction = West
+		case South:
+			b.direction = East
+		case East:
+			b.direction = South
+		case West:
+			b.direction = North
+		}
+	}
+
+	return append(beams, *b)
+}
+
+func (b *Beam) move(board [][]byte, height int, width int) []Beam {
+	switch b.direction {
+	case North:
+		b.y--
+	case South:
+		b.y++
+	case East:
+		b.x++
+	case West:
+		b.x--
+	}
+
+	return b.canContinue(board, height, width)
+}
+
+func emptyBoard(height int, width int) [][]byte {
+	var board [][]byte
+	for i := 0; i < height; i++ {
+		board = append(board, make([]byte, width))
+	}
+
+	return board
+}
+
+func count(board [][]byte) int {
+	var result int
+	for y := range board {
+		for x := range board[y] {
+			if board[y][x] == Mark {
+				result++
+			}
+		}
+	}
+
+	return result
+}
+
+func part1(board [][]byte) int {
+	height := len(board)
+	width := len(board[0])
+	var result int
+	trackBoard := emptyBoard(height, width)
+	beams := []Beam{Beam{y: 0, x: 0, direction: East}}
+
+	for {
+		change := false
+		var newBeams []Beam
+		for i := range beams {
+			if trackBoard[beams[i].y][beams[i].x] != Mark {
+				trackBoard[beams[i].y][beams[i].x] = Mark
+				change = true
+			}
+
+			newBeams = append(newBeams, beams[i].move(board, height, width)...)
+		}
+
+		if !change {
+			break
+		}
+
+		beams = newBeams
+	}
+
+	fmt.Println(count(trackBoard), trackBoard)
+	return result
+}
+
 func main() {
 	if len(os.Args) < 2 {
 		log.Fatal("You need to specify a file!")
@@ -41,5 +181,5 @@ func main() {
 	}
 
 	board := readInput(file)
-	fmt.Println(board)
+	fmt.Println(part1(board))
 }