The Maze III

Given a maze where a ball rolls in a chosen direction until it hits a wall or drops into a hole, find the shortest-distance path (measured by number of cells rolled) from a start to the hole and, if multiple shortest paths exist, return the lexicographically smallest sequence of move directions; return "impossible" if unreachable. This requires treating each roll as a weighted move and resolving ties by lexicographic order of the move string.