The Heesch number of a shape is the maximum number of layers of copies of the same shape that can surround it. For example the following shape (in the center) has a Heesch number of 4, because we can get at most 4 layers to surround it:
Given a shape, is there an efficient algorithm to compute its Heesch number? The only thing I can think of is to do a brute-force BFS search, surrounding it layer by layer. But this seems awfully inefficient.
