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23/code.go

@@ -33,6 +33,102 @@ func readInput(file *os.File) [][]byte {
 	return board
 }
 
+const (
+	Up    = '^'
+	Right = '>'
+	Down  = 'V'
+	Left  = '<'
+	Rock  = '#'
+)
+
+func (p *Point) getDestinations(board [][]byte, height int, width int) []Point {
+	var destinations []Point
+	p.steps++
+	slope := false
+	switch board[p.y][p.x] {
+	case Up:
+		p.y--
+		slope = true
+	case Down:
+		p.y++
+		slope = true
+	case Left:
+		p.x--
+		slope = true
+	case Right:
+		p.x++
+		slope = true
+	}
+
+	if slope {
+		destinations = append(destinations, *p)
+		return destinations
+	}
+
+	if p.x-1 >= 0 && board[p.y][p.x-1] != Rock {
+		destinations = append(destinations, Point{y: p.y, x: p.x - 1, steps: p.steps})
+	}
+
+	if p.x+1 < width && board[p.y][p.x+1] != Rock {
+		destinations = append(destinations, Point{y: p.y, x: p.x + 1, steps: p.steps})
+	}
+
+	if p.y-1 >= 0 && board[p.y-1][p.x] != Rock {
+		destinations = append(destinations, Point{y: p.y - 1, x: p.x, steps: p.steps})
+	}
+
+	if p.y+1 >= 0 && board[p.y+1][p.x] != Rock {
+		destinations = append(destinations, Point{y: p.y + 1, x: p.x, steps: p.steps})
+	}
+
+	return destinations
+}
+
+func (p *Point) key() string {
+	return fmt.Sprintf("%d_%d", p.y, p.x)
+}
+
+func calculate(board [][]byte) int {
+	height := len(board)
+	width := len(board[0])
+
+	start := Point{y: 0, x: 1}
+	goal := Point{y: height - 1, x: width - 2}
+
+	visited := make(map[string]int)
+	visited[start.key()] = start.steps
+	frontier := []Point{start}
+	var max int
+
+	for {
+		if len(frontier) == 0 {
+			break
+		}
+
+		current := frontier[0]
+		frontier = frontier[1:]
+
+		if current.x == goal.x && current.y == goal.y {
+			if max < current.steps {
+				max = current.steps
+			}
+
+			continue
+		}
+
+		successors := current.getDestinations(board, height, width)
+		for i := range successors {
+			_, ok := visited[successors[i].key()]
+			if !ok {
+				visited[successors[i].key()] = successors[i].steps
+				frontier = append(frontier, successors[i])
+			}
+		}
+	}
+
+	return max
+}
+
 func main() {
 	if len(os.Args) < 2 {
 		log.Fatal("You need to specify a file!")
@@ -46,5 +142,5 @@ func main() {
 	}
 
 	board := readInput(file)
-	fmt.Println(board)
+	fmt.Println("Part1:", calculate(board))
 }