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keith · Posted: Wed Aug 26, 2009 6:49 pm Post subject: Aug 26 Hard

Today's puzzle is pretty good:

arkietech · Posted: Wed Aug 26, 2009 9:59 pm Post subject:

Glad to see someone else enjoys a good "Hard" puzzle.
This one was better than a lot of the "Very Hards".

keith · Posted: Wed Aug 26, 2009 10:43 pm Post subject:

Here is my sticking point:

Stanley P · Joined: 27 Feb 2008 Posts: 20 Location: Tennessee, USA

It was the dastardly hidden pair. I never expected the hidden pair. It was, in fact, more difficult for me than most of the VH puzzles.

keith · Posted: Thu Aug 27, 2009 2:31 am Post subject:

Stan,

My arrogance says I should do these without pencil marks. After an hour, I succumbed.

Even after the hidden pair, I was stuck for a time on the pairs in C1.

I agree with you and dan, this is much more enjoyable than most of the one-step "Very Hard" puzzles.

Best wishes,

Keith

Marty R. · Posted: Thu Aug 27, 2009 3:47 am Post subject:

kragzy · Joined: 01 May 2007 Posts: 112 Location: Australia

I'm with you Marty - the larger naked sets are easy to spot. They then lead to the discovery of those sneaky little hidden pairs.

More of the same in today's H puzzle (28th).

Cheers

strmckr · Joined: 18 Aug 2009 Posts: 64

i find hidden sets easier to find when not using pencil mark ups.

(look at the givens)

all the *'s see 58 marked with @. (leaves two cells as 58 )

cgordon · Joined: 04 May 2007 Posts: 769 Location: ontario, canada

Good one!!

Agreed – harder than most very hards.

Also agreed – much easier to spot naked quads than hidden pairs. It’s the same in real life.

strmckr · Joined: 18 Aug 2009 Posts: 64

how do you find its easier to spot naked sets over hidden sets?

try not using a solver to aid in the solution or with out Pm's:

hidden sets are much easier to find over naked sets when manual non-pm solving is used.

keith · Posted: Fri Aug 28, 2009 8:43 pm Post subject:

storm_norm · Joined: 18 Oct 2007 Posts: 1741

to use or not use the sweep function Exclamation

that is the question.

with finding hidden pairs, I think using the sweep function might clutter the grid to the point you might not find them as easily.

finding xy-wings on the other hand, its a breeze with the sweep function. that goes for naked sets also.
its probably a little bit more intuitive to make the eliminations after recognizing a naked set. when finding hidden sets, its almost thinking about it from the opposite side. what two candidates can only go in these cells, thus eliminating all others from the cells. that is a little different than the naked sets which tell us the candidates that can't go in the "house" the set is already naked in.

keith · Posted: Sat Aug 29, 2009 1:10 am Post subject:

Marty R. · Posted: Sat Aug 29, 2009 1:15 am Post subject:

storm_norm · Joined: 18 Oct 2007 Posts: 1741

strmckr · Joined: 18 Aug 2009 Posts: 64

Pencil marks are the reasons that hidden sets are "hidden".

if your used to not using them you should notice that they are in fact easier to find.

hidden sets use what is given to identify (dont need pms)
(as in the example above)

over naked sets where u write down what is missing in each of n cells and comparing for identical states to form the set

howsoever in a programmers point of view naked is easier to program compared to inverting the problem to solve hidden, as bitmaps already contain the pms of all cells from a grid.

for me i rarely use pencil marks anymore unless i'm working on some er 7+ grids.

but if i have to instead of marking down all the pencil marks just use notes on the key finds. (ie where the sets are).

cgordon · Joined: 04 May 2007 Posts: 769 Location: ontario, canada