Friday 23 September 2011

Friday Puzzles #123

I’m in a little bit of a rush this week, in particular the image quality might be a little below par for now. I also plan on editing in the grand final puzzles from the Times championship last week a bit later, but for now, you’ll have to make do with this yajilin. I think there’s enough here to bump it up to a medium. Enjoy!
    #153 Yajilin – rated medium
(can't find the old image.  Meh.)
EDIT and with alternative Akari-style presentation:
   #153 Yajilin – rated medium
 See also this link for an interactive web version, courtesy of Otto Janko.

All puzzles © Tom Collyer 2009-11

SECOND EDIT And for those who are interested, here are the puzzles from the grand final for the Times Sudoku championship. On the day, these must have taken me 20+ minutes, but when republished in the newspaper later in the week, I clocked 14.10. Perhaps some of that was familiarity, but I’d argue that only made a difference with one of the puzzles (#4). I’d even argue that 14.10 felt a little slow, and as I posted in a comment in the previous entry, I reckon the crème de la crème could be much closer to an aggregate 10 minutes.

As with last year, I don’t have any sort of permission to reproduce these, so I’ll take them down if requested, but no-one complained last year and I think it’s fair use in so much as this will provide highly interesting international comparison. Since there is no copyright in the paper, I can’t be 100% sure that these are from the Puzzler Media generator, but I think it’s more than likely that that’s the case.
    2011 Times Su Doku Championship Grand Final #1

    2011 Times Su Doku Championship Grand Final #2

    2011 Times Su Doku Championship Grand Final #3
And finally, my own personal nemesis – and as with the case with most nemeses there’s no particularly good reason why this would be the case! 
2011 Times Su Doku Championship Grand Final #4


  1. Copy this to the address bar to solve this nice puzzle online:,,2e,,,,,,/,,,,,,,,2s,,/,,,,,,,,,/0n,0n,,,oe,1n,,,,/,,,,,,2w,,,/,,,1w,,,,,,/,,,,1s,1s,,,2w,1n/,,,,,,,,,/,,1n,,,,,,,/,,,,,,,2w,,/

  2. This was ok, with something nice coming from the paired vertical 1’s that I liked.

    I mainly solved it so I could comment on how useless some of the clues are, particularly those 0’s in the upper-left, which is why I still prefer the Akari-like clue style for this type, especially when the geometry of clue cells acts a lot like a Simple Loop and doesn’t need numbered clues to drive the local logic. I think the back shading also makes the clue pattern pop a bit more.

  3. “alternative Akari-style presentation”—

    In this case you have to modify the rule that black cells must not be adjacent. Worse, you have to distinguish between given black cells and black cells drawn by the solver.

    Maybe a better solution would be a white zero without an arrow.

  4. Hi Otto, thanks for the feedback!

    I’ve been conscious about the whole thing with shaded squares. It’s not the first time I’ve experimented with alternative yajilin presentations – indeed I have yajilin puzzles that simply would be far far poorer with the classic presentation. See:

    Those times, I decided to use grey squares, to differentiate between black squares. Perhaps it’s simply a question of wording – “shading” cells rather than “blackening” them? I think where I agree with Thomas the most though is the alternative presentations highlights the inherent similarities between this type and Simple Loop – something that can often be lost on newcomers with the classic presentation.

  5. I’ve dealt with this concern by either saying “unused cells” are pointed to by the arrows, and these don’t touch, or using gray instead of black with the clues. Just because the standard Yajilin uses blackened squares and too many numbers doesn’t mean the correct presentation needs to use all of these things. “Black squares” is not a necessary thing, just that some cells don’t get used. And as an in-between puzzle style with elements of Simple Loop, I like the alternate a whole lot more than “pure” Yajilin which has rarely excited me.

    Also, thanks for posting the Times puzzles. I’ll share my times later if you actually care, but I’m guessing you don’t want to know them anymore than I would, when this is a championship they won’t let me compete in.

  6. Going through them this afternoon, I actually stumbled on #2, taking 4’13” on it, not that the next moves were hard, just not smoothly found. The rest were (1) 2’27”, (2) 2’41”, and (3) 2’42”. I reckon you are right that a classic specialist would finish in 10 minutes or faster on these.

    I was pleasantly surprised at the response to the Killer (the second one I’ve written) but using good extra-region constraints is certainly something you’ll get much more from hand-setting than otherwise so I think the rarity of encountering them is what makes them very cool.

  7. my timings for the 4 sudokus of the grand final are 3:52 , 5:00, 6:12 and 3:56


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