You are at position [0, 0] in maze NxN and
you can only move in one of the four cardinal directions (i.e. North, East, South, West).
Return the minimal number of steps to exit position [N-1, N-1]
if it is possible to reach the exit from the starting position.
Otherwise, return false in JavaScript/Python and -1 in C++/C#/Java.
Empty positions are marked .. Walls are marked W.
Start and exit positions are empty in all test cases.