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25 May 2007 @ 09:29 am
Today's Nikoli Championship Puzzle  
So it was a good morning on Nikoli.com. To be honest, I woke up about a quarter-hour before the contest and was not fully awake when it started. I was sure I'd lost when I got to 6 minutes and began to force things with nishios (particularly after I realized I'd taken minutes to place some fairly easy digits as my solving video clearly shows). But apparently the tough parts were tough enough to slow everyone. I am now the World, and Nikoli, Sudoku Champion. The latter comes with a nice t-shirt. W00t!

As an aside, I just realized that character limits on comments (you get 100 on any Nikoli puzzle) is a challenge for English speakers on a Japanese site. A hundred Japanese characters can form many more words than 100 English characters. I often wonder, when I see a long stretch of japanese from another competitor, if they are waxing far more poetically on a puzzle than I can in my language under the character constraint.
THrpipuzzleguy on May 25th, 2007 01:50 pm (UTC)
Congrats! Though I'd suggest taking out the minor spoiler in your comment, and maybe LJ-cutting this entry as well.
motrismotris on May 25th, 2007 02:16 pm (UTC)
I believe I took care of both - as there aren't daily puzzles of my types that I comment on, I was a bit careless with the standard etiquette.
phat_joephatjoe on May 25th, 2007 02:13 pm (UTC)
I kinda sudoku'd myself out a while back by continually playing a computer version for a few months until I had whittled down my top speeds about as much as seemed possible, but I don't think I ever got into the higher level strategy of the puzzles. (I have no idea what a "nishio" is... well, I didn't until I just checked on Google.)

All this talk about sudoku competitions though makes me wonder how competitive my raw skill already is, how much I could refine it, and how competitive I would be. Let's say I was entertaining the notion of competing in October. Do you recommend any online resources to this end? I have a kind of general disdain for sudoku and yet I believe that I am probably pretty decent at it, so I am compelled to find out more.

motrismotris on May 25th, 2007 02:24 pm (UTC)
Nishio is my way of saying I looked at some fairly locked digits and assumed one was true to see if it led to a contradiction. To be honest, as its typically over just one digit, it could also be called "painting," although this is not always the case.

I don't really have any recommended resources as the "generic" sudoku vary somewhat in the skills they require based on the source. If this is a championship that involves Will Shortz puzzles, his books may be the best place. I wish there were more data on particular sites about solving times, but you might start to catalog some of your times. Mine aren't the best to compare to, but as a very lower bound you could solve the UK championship puzzles I linked to here and compare with their champion (who was solving on a poster), and me (who was solving on paper).

phat_joephatjoe on May 25th, 2007 06:14 pm (UTC)
Thanks, I'll check those out! Of course, I should brush up a little first... wonder if I still have that Sudoku program...

When you say "generic", I assume you mean as opposed to the variations (toroid, LED, etc). Perhaps as a side effect of the fact that I don't have any real fixed "routine" for solving generic sudokus, I have never found the variations to be inherently harder... just different. I remember reading about lots of people having trouble with a toroid one last year, and I wondered if it was just a difficult puzzle on its own merit or if the competitors were actually tripped up by the variation.

motrismotris on May 25th, 2007 06:44 pm (UTC)
As you suggest, I agree that for most top sudoku solvers, a puzzle being a variant isn't really much of a ripple. Putting in a diagonal constraint? No problem.... There might be a subset that is not as good at some of the mathematical ones like killer, but a geometric variant is not, itself, going to throw people who are good at visualizing placements for the numbers 1-9 already.

The toroidal at the first WSC was very difficult and I'm amazed I finished it (no one else got very far at all - just one digit in to be exact after fifteen minutes). I think the difficulty stemmed more from the lack of really any singles/pairs to use as work-ins as you'd see in a regular sudoku. It didn't matter that the rows/columns had wrapping properties when you couldn't force a placement. There is one digit most mortals can place, and then a lot of staring. The best proof though is to try it yourself so look here for that puzzle.

I think I'm actually using "generic" not for classic sudoku, but for mass-produced computer-generated classic sudoku. While Will's books sell well, I find the puzzles which are on lower quality paper and with no symmetry to speak of, to be less than ideal. Even Wayne Gould's puzzles seem a step forward, with a good difficulty rating, although I tend to only solve Nikoli sudoku if I have a choice as sometimes they interest me with hidden themes. It is probably a point of contention I have as a puzzle constructor myself, and I addressed it two blog posts ago, but "generic" as I'm using it is definitely a subset of "classic" or "vanilla" sudoku.
phat_joe: milk maidphatjoe on May 25th, 2007 08:42 pm (UTC)
Ahh I should have realized. By the way, I meant to tell you that the United States sudoku grid was beautiful.

phat_joephatjoe on May 30th, 2007 05:40 pm (UTC)
That toroidal is very very hard. I have spent more time than I care to admit staring at it, and I've only placed about 6 digits. I expected it to pick up steam once I got that far, but it hasn't. I did figure out an interesting property of the layout which allowed me to get as far as I have, but it has done so much. (I haven't resorted to guesswork just yet.)

So how much time were you allotted, fifteen minutes total? And how the hell did you finish it??


(stupid lj commenting weirdness)
motrismotris on May 30th, 2007 06:34 pm (UTC)
[attempted to be as spoiler free as possible] it was 15 minutes total, and it was on stage on big placards. I think its impervious to much guesswork as you won't reach contradictions early. To solve it, I recall finding a property about the shape that mattered, with my eyes drawn to it by two of the digits. I could "test" a possible contradiction and that got me about 6 digits. Using the same kind of thinking, but in a harder sense, gave me another digit that then cracked enough of it to get me to about 12 digits. Time was running short, so I decided, as patterns were arising, to assume something about the puzzle. That assumption proved true, and I finished just before time was up.
phat_joephatjoe on May 30th, 2007 09:52 pm (UTC)
Well it took me more than 15 minutes just to find that first property, and the first time I tried using it I ended up misapplying it and having to scrap the page. I bow to your superior pattern recognition skills!