Zen Puzzle Garden is NP-complete

• Once moving on sand, the monk continues to move in a straight line until he encounters either a walkable square (in which case he moves onto it) or a a raked square (in which case he stops moving). The monk may not turn corners during a single move while moving on sand. These two rules are central to the challenge of the game – if the monk could be moved over the sand on a square-by-square basis then most boards would be trivial to solve.