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naz · Guest

Hi,

Sometimes back aardy pointed out towards two solutions to very hard puzzles. Here are two solutions to this very hard puzzle of 25 September 2005.

Original Puzzle

-7- --- 1--
--- 7-- -64
1-- 9-- 8-2

8-1 --- -93
-2- 5-9 -8-
96- --- 4-1

6-4 --8 --7
79- --6 ---
--5 --- -1-

Solution No 1
572 864 139
389 721 564
146 935 872

851 647 293
423 519 786
967 283 451

614 358 927
798 126 345
235 497 618

Solution No. 2

279 864 135
538 721 964
146 935 872

851 647 293
423 519 786
967 283 451

614 398 527
792 156 348
385 472 619

cheers,

naz

chobans · Joined: 21 Aug 2005 Posts: 39

Solution #1 has two 2s in column 5 and two 7s in column 6.

alanr555 · Posted: Sun Sep 25, 2005 10:34 pm Post subject:

Why was this one labelled "very hard" whereas the one on Sept 20th
was merely "Hard"?

I suspect that the grading is biassed towards or against some methods
of solution. I find that my methodology works very well with "very hard"
and their solutions emerge relatively easily but some of the medium and
hard puzzles take much more work - usually because fewer cells resolve
from my initial search for "mandatory pairs". That said, there are some
that resolve completely from "mandatory pairs" (plus simple elimination
by logic of course) without resorting to a solution grid.

Widening the subject, I find gradings in different puzzle sources to be
quite confusing. Some do not even have clarity (eg "challenging") as
to where they are in relation to other descriptors. It is a virtue of this
site that easy, medium and hard are well understood terms!

Alan Rayner BS23 2QT

samgj · Posted: Mon Sep 26, 2005 11:43 am Post subject:

alanr555 · Posted: Mon Sep 26, 2005 10:51 pm Post subject:

> The grading method is subject to tinkering as it has yet to satisfy me
> entirely. Right now, any one of 4 or 5 different logic steps, even if only
> required once, makes a puzzle hard. The requirement to apply "hard"
> logic 3 or more times during solution bumps it up to very hard.

Thank you for this explanation.

> Incidentally, by your description above, I think all medium puzzles
> should be resolvable without your solution grid -- that is simple
> elimination from definite numbers is enough. At anything more than
> beginner level, people solve medium puzzles using more advanced
> logic than is strictly required.)

Great - a new challenge - to solve Medium puzzles without going into a
solution grid. Of course this may prove to be "hard" in practice!!

Alan Rayner BS23 2QT