Labyrinth

You are given an $n \times m$ grid that represents a labyrinth. Your task is to determine the length of the shortest route from the square A to the square B. Each square is either floor (.) or wall (#), and all squares along the edges of the grid are wall.

You may assume that $1 \le n,m \le 20$. If there is no path, return $−1$.

In a file labyrinth.py, implement a function count that returns the length of the shortest route.

def count(r):
    # TODO

if __name__ == "__main__":
    r = ["########",
         "#.A....#",
         "#.#.##.#",
         "#.##...#",
         "#...B#.#",
         "########"]
    print(count(r)) # 7