Plank Puzzle No.15 - Fiendish

Cross the swamp from left to right using the available tree-stumps (fixed) and planks (moveable). Full rules can be found here. The complete set of all 15 puzzles can be found here, which may work better for some browsers.

Sorry, this is a Java applet.


Click on Restart to restart.
Click on Undo & Redo to step through previous moves.
Click on Replay to restart with redo active.
Click on Load/Save to restore/capture a move sequence.

Click on the play area to pick up or put down a plank. Accessible stumps will be automatically highlighted for you.


The optimum solution to Fiendish can be found here.

Fiendish was devised by hand, over a period of several days. My sole aim was to improve on my previous best (Route-66) which I had stumbled on more by luck than judgement, and was a huge leap forward in its time. A nifty windows-based (C++) plank-puzzle editor/solver (by applet author - Graham Rogers) was used to verify the solution. Fiendish is actually shorter than Route-66, but more complex and compact, as (hopefully) illustrated in the following table. Note I (used to*) measure plank puzzle complexity by move-over-span ratio which is why I rank Fiendish above Route-66. Fiendish and Route-66 are the only puzzles to date (03/03/01*) with a move-over-span ratio greater than 1 (meaning the number of moves actually exceeds the number of possible plank positions).

   Route-66  Fiendish
Grid  9x9 (square)  8x8 (square)
Planks  3 (1+2+3)  4 (1+2+3+4)
Shortest solution  66 moves  57 moves
Span count  54  40
Move/span ratio  1.22  1.42

(*) In late March 2001 Pascal Wassong well and truely smashed my move-over-span ratio record with a plank-puzzle of his own invention entitled The Centrifugal Force. This puzzle requires an incredible 342 moves and has a move-over-span ratio of 4.62. Try it here.

concept & puzzle design – © Andrea Gilbert 2000-01
applet – © Graham Rogers 2000-01