Done

Me too. It's impressive how much easier this one was than yesterdays...

I worked a couple of hours on yesterday and gave up on it.

I can't believe I actually had enough of my brain left to finish today's after yesterday's expert.

well, i can vouch that checkpoints get saved across days... i left yesterdays with 5 filled and it is still that way. (was hoping maybe itd autosolve or something) ;)

todays was hard enough - im leaving yesterdays for someday i need the torture... :)

go

done

yesterday's was ugly. This one is easy.

Hoping to finish today's with time enough to go back and finish yesterday's.

go

Hello Caveman, thanks for the hint yesterday. It helped even though I was very slow to figure it out.

yah, it was like 20 steps in :)

how long did it take to finish?

All day, on and off.

todays is much easier

The most satisfying thing was knowing I didn't have to guess.

yeah, same here

before that site you gave me, i thought you had to guess for experts

done

You may still have to guess sometimes.

Remember Computer Science? Sudoku is NP complete.

I had this theory that whenever I "solved" one, I had made a favorable mistake somewhere :)

I've forgotten what NP complete means.

NP complete or NP hard...

:))

"Not Possible" to Complete?

Basically there is no technique or finite set of techniques to solve all sudoku puzzles (in the general case of arbitrary sized grids).

So, it might be that following a trail won't show you anything till the last move, which is the same as guessing.

I guess...

So the scan raid techniques will fail ?

Scanraid is continually adding new techniques and he is looking for puzzles that can't be solved with any of his current techniques.

Hmm, he should put up the list of puzzles that aren't currently solved...

Since we only do 9x9 puzzles and there is a finite number of them possible (someone has calculated it), it seems likely that there is a finite number of techniques needed to solve 9x9 grids.

But it's possible that one technique may be no more clever than a guess.

Hmm, i just started calculating the number of 9x9 grids... wondering if I should remove symmetric puzzles

Caveman, did you do today's without greens?

9 factorial times 8 factorial ... times 2 factorial times 1 minus the number of puzzles that don't have unique blocks divided by all the rotations and permutations on the rows and columns and there you have it.

no, I'm still in the afterglow of solving wednesday's expert w/o greens :)

You mean Tuesday's expert? There has been an expert every Tuesday this month so far.

I don't think DrWho's formula takes count of forbidden cells within blocks.

Read it again.

I don't know how to do that, but I mentioned it.

or which cells can be empty?

I only gave an outline of calculating the number of completely solved puzzles, not the number of clues that could be given.

I don't think that would be possible to calculate.

ah, so "puzzles that don't have unique blocks" is ...

oooh, wikipedia Mathematics of Sudoku

We were talking of classifying the NP-ness of sudoku by the finite number of puzzles to feed any algorithm

I guess there are a set of algorithms that can be applied to a sudoku solution to walk it back to a minimal yet still uniquely solvable puzzle

later all

Bye,

Dr, is it possible to construct a Sudoku without a computer?

Sure, why not? The computer programs were developed because the first sudokus appeared in magazines that needed a new puzzle every week or maybe month. So they couldn't afford the time of hand generated puzzles.

How would one go about constructing one by hand?

Anything a computer can do, a person can do better (but slower).

Yes, but at some point slowness will be a limiting factor.

I would start by generating the solution. Scramble the 9 digits for the first row. Then place digits in the remaining rows watching that you don't violate the constraints of uniqueness. Finally try subtracting all but about 18 - 25 of the digit and see if the puzzle has a unique solution by hand solving it.

Gauss wrote a paper on generating Latin Squares which might interest you. If I can find a link I will pass it on.

that was a nice break from yesterday. one naked pair unlocked the whole thing

Oops, my memory is bad, it was Euler that wrote the paper I read. In fact some people refer to them as Euler Squares.

I've found a complimentary pair of pairs, one naked and one hidden, but I only got 1 digit from them.

No wait I found a 3rd hidden pair and a complimentary naked triple...but still only 1 digit solved from them.

I think I'm over the hump in today's, no greens, and I don't think I've used anything but crosshatch and virtual crosshatch.

Uh oh. But I've made some mistake.

I think my checkpoint is good.

maybe i was just in the groove today :)

Congrats skizzy. Maybe I burnt out on yesterdays.

well, i still haven't finished yesterday's, so there's that

i've got a bit of a backlog since i decided not to guess for experts and not to use greens for hards -- and then work got really busy

Well, I'm going to bum out and use greens on today's. Getting too tired to think.

Darn. There's a loner I missed. How did that happen?

Well, it was pretty open, 4 or 5 open cells in each constituency.

Oh, darn it. I've made a mistake, probably before my checkpoint. I'll have to start again. Later.

my mum's just told me that in a book of sudoku puzzles she has, one is 16 x 16 with hexadecimal numbers

yeah, those are fun, if a bit headache-inducing

done. such a relief after yesterday's fiasco. Didn't even need intersections - all cross-hatching, naked doubles and triples, etc.

UTH -- A translation of Leonhard Euler's paper "De Quadratis Magicis" (On Magic Squares) can be found at:

http://arxiv.org/abs/math/0408230v6

Thi
s page is just an abstract, in the upper right hand corner there is a link that downloads a PDF file of it.

I wouldn't believe yesterday's is possible except for the fact that are still elite people!

the most difficult I've seen in here - or is it just me?

drwho said it had a difficulty score over 100

I am greened and don't know where to begin

Yes, 101, the highest score for any puzzle published here.

I've never gotten too deep into the workings of those XYZ swordfish, jellyfish, clownfish theories..... imagine this one is impossible without all that techno stuff

The advanced techniques I used were, X-Wings, Almost Locked Sets and Alternating Inference Chains.

gives me a headache just reading your message

alright, enough of this. i've got some pants to patch and bikes to fix

did you get yesterday's skizzy?

nope!

I'm on my third try

i'm still on my first try -- i'm going to go back and read the hints that drwho said he used

where do you find them?

all those advanced techniques take a while to learn, but they're fairly intuitive once you do. that's why i'm confident that i'll be able to complete the experts if i just leave them for later

I mean I know what he said he used, but where do you find the descriptions of what they are?

in the chat log -- read over today's and yesterday's

I agree - I did look into them a while back, but usually can manage to do the puzzles without too much of that - this one is different

oh, that

http://www.scanraid.com/AdvanStrategies.htm

thanks!

but i would suggest actually reading over the chat logs, too, because there are some slightly more specific hints

okee doke! muchas grasias!

later!

now that one was fun.

maybe I should do today's and come back to this one

but I don't know if what I did so far is right and if I save it and it's wrong, I'll have to start over..... uggggg

??? if you don't save it you'll have to start over too ???

back to the beginning greenies

HA! Yesterday's is done!!! No theories - just good old fashioned logic!!!!!

WTG Mama

*curtsey* thank you, dr!

t'was a challenge though .....

today's is better I hope

I do applaud your abilities with the theories though - maybe someday I can hibernate for a bit and think them through

Theories are nothing more than old fashioned logic in fancy dress.

geez... on the surface, today's doesn't look much better

good point, dr.... never thought of it that way

I gave in and went green. Like UTH I had missed a missing digit scan. After that it was like shooting fish in a barrel.

You tried to do it without even greens? wow

I usually do them without green, except the experts.

you talking about yesterday's or today's?

I think I have done 2 experts without green.

well now that I see you are a computer programmer.... makes more sense!

Today's

I just greened today's... we'll see what happens

I try to do with no green first.... sometimes works

I can do hard ones without greens about half of the time.

hi orange!

Good morning

Occasionally an easy requires green for me too.

dr - what do you mean by "missing digits"?

Well, yeah, it really depends on the puzzle.

I'll admit to using greens on the occasional easy/medium one.

the ratings can be misleading sometimes I've found

UTH calls them loners. When you look at an empty cell and its buddies to see what's already there. If only 1 digit is missing it must go in the empty cell.

ok - that's what I thought

thanks

Difficulty score for today's: 29. After yesterday's it didn't seem that hard.

I didn't find time to finish yesterday's yet. Any hints?

But I did have to use the little green numbers, so maybe...

I filled in the 1s first, Orange

Lots of good hints in the chat log from yesterday.

Nick are you on?

Alright then. I got a good ways into it and made several eliminations, but had to stop due to life interceding. lol

I am in the barrel, dr!

Better get out or you'll get shot.

or should I say outside the barrel, shooting in? LOL

Oh, good, I only want to shoot fish, bears are out of season.

LOL!!! That was much easier than yesterday! did both in an hour and a half - too much time to spend, but worth the effort I guess

You are improving your mind, never a waste of time.

I'm just going to green this one, I'm feeling lazy.

exactically!

go ahead and green, orange!

it is pouring down rain - so NOT FAIR for a Saturday!!!!!

Clear and sunny in Minneapolis. We had the rain yesterday.

worked 55 hours this week - was looking forward to R & R in the pool.... grrrrrrrrrrr

Well if you're going to get wet anyway...

no fun without the sun

I've had the last week and a half off :). Back to school Monday though.

Summer session? You must be in a hurry.

I'm a little behind.

or very ambitious

Well, that too.

Like the butcher who backed into the meat grinder...

...he got a little behind in his work.

I only have 31 credits after a full year, so I'm doing 10 this summer and 17 in the Fall.

I need 110 to transfer, and I was hoping to get there in two years.

LOL, dr

I seem to remember 15 credits was considered a full load.

what is your major, orange?

Are you on the quarter system or semesters?

Quarterly

Double major. Music theory and math ed.

Ah...so 2 years would normally get you 90 credits and you want 20 more.

nice - my favorites

or two of them anyway

What instruments do you play?

Piano

I play a little piano, very poorly. I do better with trumpet and euphonium.

I play piano too!

but rather rusty now

I played trumpet and baritone a long time ago, in school. A little percussion also.

oompa, oompa, oompa pa

I think the timpani was my favorite from back then

we have a timpani with one of the choirs I sing with - way cool

It's hard to take the timpani home to practice :-).

Tons of fun to play :)

need a rather large backpack

And a strong back.

rain rain, go away, come again another day.......

can't be heavier than the piano though - that was always a problem I remember

how ya doin, orange?

Getting distracted

hope it's a fun one!

this rain is depressing.... think I'm going to go shopping!

haha. I wish I had more than $20 in my checking account.

that's why you are going to school, orange - so in the future you won't have to ever worry!

Actually I'm going to school just because I want to. Although I suppose I might go to work when I'm done.

LOL.... yeah, that would be a good idea!

We'll see.

depends on how far that $20 can stretch, I suppose!

Well, my school offered me a part-time job this summer, so I'll be making a little bit.

I also do peer tutoring, funded by the school, which is $9/hr, but only a few hours a week (if that)

better than nothing!

Pays for all the lattes I buy.

well, I'm going to go do something with this wet day - thanks for the chat and have a good day, orange, and dr.who if you're still here

Have a nice day, then.

thanks - you too!

Bye Mama

before I go, can one of yo see if my profile updated? I tried but it doesn't look like it worked right

all I had before was my location

Appears that it did

How would I know? What is new?

ok good! thank you......

I think the lengthy bio is new :)

that's why I said all I had before was my location

The poem?

I copied it from my Babble profile......

ok yes - it's good then

thanks! see ya's in the funny papers......

Today's quite easy. A little virtual crosshatch, open pairs, that's all. But the pairs not easy to see without green, as they are separated by a long distance and caused by different factors. So I used greens and got through it quickly. Too bad I made a mistake the first time.

I will agree... Compared with yesterday's expert... this was a cakewalk

go

I'm doing yesterday's, very slowly

i am doing today's, very slowly, lol

hee hee

I did today's very slowly ----and failed!

done

minimal greens needed

I still have only 5 numbers added so far

I didn't use any greens for today's

I didn't use any greens for today's

I've just added 'X-Wing' to my repertoire. I found one in today's puzzle. Done!

finishes yesterday's and don't know how I did it!

Piece of pie . . .

done

workin on it

had to use greens but I finished