code: def territory(self):
          
          cache_key = (
              self.board.length, self.board.height, self.uid, self.index)
          if cache_key not in self.territory_cache:
              vector = self.compute_territory()
              self.territory_cache[cache_key] = vector
          else:
              vector = self.territory_cache[cache_key]
          return vector
docs: Return the cached territory occupied by the piece.