## Sunday, February 14, 2010

### A Curiously Clever Chess Puzzle

It's been some time since I've posted any logic puzzles, and I don't remember ever posting a chess puzzle, so today I'll kill two birds with one stone. In fact, the following position represents two puzzles in one. (You don't have to be a grandmaster at chess to solve it, so even if you only know the basic rules of the game you should give it a try.)

The first part of the puzzle requires more logical thinking than chess skill. Explain how this highly unlikely position could possibly be reached in a game. You don't have to show all the moves, but you should be able to convince yourself that it is a legal position.

Second, it's white's turn to move. Show how white can checkmate black in at most four moves.

I'll give the answer and the original source of this puzzle in an upcoming post. (Update: the full solution is up.)

The diagram image is courtesy of the Online Chess Diagram Editor.

William Shields said...

This position I don't believe is actually possible.

The black knights can take all the white pawns so that part is explainable but the black king and queen have swapped places. I don't see how that could have happened.

As for checkmating in four moves? Can black move? If so, that's hard. I'm sure there's something I'm missing but black could easily stop a checkmate within 4 moves if allowed to move.

Bill the Lizard said...

William,

"The black knights can take all the white pawns so that part is explainable but the black king and queen have swapped places."

This is exactly the line of thinking that I took when I saw the problem, so I'm relieved to know that it's not just me that didn't see the solution right off. What will really drive you mad is that this is the start of the correct line of thinking. :)

I will add the additional clue that you must solve the first part of the puzzle before the second part is even possible.

William Shields said...

Ah I think I've got it (the first part that is)... read on only if you don't want to know the answer (or at least what I think the answer is).

In fact I'll rot13 it (www.rot13.com):

Gur obneq vf erirefrq. Abeznyyl gurfr guvatf fubj juvgr ng gur obggbz naq oynpx ng gur gbc ohg gurer'f ab ernfba guvf zhfg or gehr.

Fb jung lbh'er npghnyyl frrvat vf gur juvgr naq oynpx cvrprf unir ynetryl erirefrq naq gur oynpx cnjaf ner ba gur gurve friragu enax, abg gurve frpbaq. Guvf zrnaf gung nal gung trg gb gur arkg ebj jvyy cebzbgr (cebonoyl gb dhrraf). Ohg zber vzcbegnagyl gurl'er oybpxvat gur oynpx cvrprf sebz zbivat naq juvgr pna zbir uvf cvrprf gb gur fvkgu enax (eryngvir gb pheerag cbfvgvba) jvgubhg orvat gnxra (rkprcg ol gur oynpx xavtugf).

N fvatyr juvgr xavtug 5 fdhnerf nobir gur juvgr xvat jvyy purpxzngr oynpx. Gur bayl jnl oynpx pna trg hafghpx vf ol zbivat gur xavtugf, zbivat cnjaf (juvpu jvyy cebzbgr gurz, gura pyrnevat gur ovfubcf naq gura zbivat gur xavtug. Fb vg jvyy gnxr 4 zbirf gb zbir gur xvat naq juvgr unf 4 zbirf orsber gung unccraf. Fb juvgr whfg arrqf gb svaq n cyna jurerol gur xavtugf naq 1 cbffvoyr cebzbgrq cvrpr pna'g vagresrer jvgu gur xavtug zbirzrag gb gur purpxzngr cbfvgvba (be bar bs gur nygreangrf).

\/\//\ Wim said...

.3D ro 3F ta thgink s'ti s'teg etihw nehw etam s'ti ,lleW .dnefed nac taht thgink ytsan a sah kcalb yletanutrofnu tub ereht ti teg ot sevom eerht sekat tI .thgink kcalb eht ekat ot deriuqer si evom erom eno oS

(And yeah, it's a big spoiler!)

andrej said...

Position is wrong, shoud be black queen on black square!?

\/\//\ Wim said...

Nope. Position is correct! Think outside the box. Look at the problem from a different direction.

Galilyou said...

It's upside down :) I got it (after a while of thinking, though) it's pretty cool one. Thanks Bill .. Here are the wining moves, Rot13ed :)

1-Ap6 Juvgr vf guerngravat Ar5 sbyybjrq ol AQ3 zngr!
1- As3 gelvat gb oybpx juvgr sebz zbivat Ar5
2-Ao4 ntnva guerngravat Aq3 zngr, gur bayl zbir sbe oynpx abj vf
2- Ar5
3-Dkr5 naq gurer'f abguvat gb fgbc juvgr sebz Aq3 zngr.

Bill the Lizard said...

Yes, William Shields, \/\//\ Wim, and Galilyou have it. Thanks for obfuscating the answers posted here. I'll start posting a link to rot13.com to make that a little more convenient when I post puzzles in the future.

I'll have my full answer posted shortly.