Tuesday 14 March 2017

2017 Sudoku GP: Round 3 Czech Republic

So on to round 3 of the GP.  Again I'm writing most of this straight after solving without being able to reference the results.  The authors this time were individual world champion in waiting, Jakub Ondrousek, and probably the world's most prolific Sudoku author, Jan Novotny.

To start off, I think that the balance was better than the previous round, but it still wasn't quite right and the puzzles didn't quite have the redeeming feature of being as dazzling brilliant as Bastien's puzzles.  Don't get me wrong, comparing less favourably than Bastien is nothing close to an insult; these puzzles were good, and occasionally great, but nevertheless the comparison is there and I'm calling it as I see it.

I should probably also draw some attention to controversy before the round.  I didn't see this, but apparently the instruction booklet was leaked onto an external website before it went live on the GP website.

EDIT: exactly how this happened has now been explained - in the interests of balance I would encourage you to read what Jan has to say. I do have some sympathy for the desire to encourage new solvers.

However my opinion is this remains inexcusable - and whilst I doubt many solvers gained much of an advantage from this, it still looks bad and definitely tarnishes the reputation of the WPF and the GP in my eyes.  I can only imagine how frustrating this will be to the competition director.

That unfortunate episode aside, here are how I rate the vital stats for the round:

Enjoyment: 5/10
Classics: 3/10
Favourite Puzzle: Pointing Differents Sudoku

Let me add again that enjoyment for me is a personal thing, and is affected by how well I thought i was solving as well as the overall quality of the round - which by and large was of a good standard.  Without further ado, here's the review:

1-5 Classic Sudoku (15, 12, 12, 10, 54 points)

Just looking at that points distribution tells you the whole story.  The first four were easy to the point of being trivial.  The last - I've confirmed with scanraid - was a guessing puzzle.  These always leave a bad taste in my mouth and I whole-heartedly wish they would stop featuring in competitions.  Please authors and competition directors, enough of these puzzles!

As for the first four puzzles, although you can see there was a visual gimmick with first the Czech flag, and then a C, then Z, then E theme, I think this is a prime example of where the theme of the puzzle proves to be a negative rather than positive.  Nice enough puzzles I suppose, but these were simply too easy.  The fact that the classic contingent made up less than 100 of the 600 points on offer also points to a bad balancing of the competition, in my opinion.

6 Overlapping Sudoku (44 points)

I suppose you might generously say that overlapping might count towards the classic contingent of puzzles, which puts the balance up to a less unflattering 25% of the points for classics. The puzzle solved nicely, although I do wonder about the presentation here. I'd be interested to try this with one of the overlapping grids shaded grey - I generally find the dotted lines for the 2nd grid to be a little distracting - but it's hard to say whether this can definitely be improved without a bit of experimentation. Aside from this, it started a run of "CZ" themed variants.

7 Diagonal Sudoku (47 points)

A nice enough diagonal puzzle, with a CZ theme.

8 Odd Sudoku (21 points)

There were probably more givens here then strictly necessary, but given the remaining variants in the round were all quite difficult, a nice easier variant was definitely welcome. Again with a CZ theme.

9 Nonconsecutive Sudoku (68 points)

Personally, I prefer "Non-Consecutive" but there we go. Not a particularly polished solving experience, it nevertheless had a fairly narrow solving path which might have left some solvers stumped for a while. Another CZ here!

10 Fortress Sudoku (58 points)

I didn't have time for this in competition, which is probably wise given recent experiences with fortress puzzles. After time, it solved nicely enough. Yes, another CZ theme here!

11 Mathdoku (77 points)

I wasted a lot of time on this during the competition, having felt my way into what felt like an opening. I had then convinced myself that I'd made a mistake. Solving it after time it turned out that I hadn't, I just hadn't considered one remaining option - the correct one! This being the biggest pointer in the competition, this was definitely annoying! Also a temporary reprieve from all those C's and Z's.

12 Pointing Differents Sudoku (60 points)

The clear star of this round, combining elements of diagonal and anti-diagonal all into one puzzle. It was a little fiddly to finish at the end, but really I'm splitting hairs with what was really an excellent puzzle. And the last of the CZ's to boot!

13 Fuzzy Arrows Sudoku (58 points)

I didn't get the logic with this one - after wasting a lot of time on an abortive effort with this one, I managed to guess my way through. Maybe I've missed something clever here, but that in itself is enough to take some of the enjoyment away from solving.

14 Lonely Number Sudoku (64 points)

The massively contrived instructions could only ever point towards a one-off gimmick - I can't see any other authors making much more variant with this type. Once you realised that the lonely number had to be in R5C5, this basically reduced to quite a tricky (but otherwise unspectacular) Touch Sudoku variant. I was quite pleased to get this out in the last 7 or so minutes, whilst fixing what would have been an irritating error with about 10 seconds to spare.

So, 12/14 solved in time. There were definitely a couple of tricky puzzles here, but I don't think this will prove as difficult as round 2 and so with the points that I left on the table I'm not going to end up with a particularly good ranking. From a personal perspective, I wasted far too much time trying to do the 5th classic without guessing, and then got bogged down with Mathdoku and Fuzzy Arrows. This happens every now and again, particularly when I'm not quite fully on my game. I would say there's always next round, but I am co-authoring the next round with David McNeill and so won't be taking part.

Top 3 (preliminary results)
1. Tiit Vunk (855.7 points)
2. Seungjae Kwak (809.8)
3. Prasanna Seshadri (746.7)
As a general comment, it seems like there is a consistent pattern to be observed.  Last year the top finisher was typically done in 60 minutes (900 points).  This year the top finisher is closer to 65 minutes (850 points) - an early indication that points towards the 2017 series being slightly harder.  Alternatively, maybe we collectively haven't quite warmed up yet.  Time will tell!

As for the Brits:
37. Tom Collyer (465)
45. Mark Goodliffe (431)
65. Heather Golding (366)
Bad luck to Mark, who had submitted 13 answers with 2 errors - without these it looks like he was pushing top 20 for the round, which would have been the best showing so far.  Also good to see other UK solvers within an easy puzzle of the top 3: Neil (8 points) and Ned (23 points).


  1. For next year, what about posting PGP, SM, PR too? :)

    - Minyoung Joo

    1. I don't have the time for all of that. I suppose I find it difficult to let go from the sudoku gp!

  2. Interesting write-up and I am looking forward to the UK Round already.
    I see that you too had struggled on the Fuzzy arrows which,in line with its name, had a fuzzy solve path . However,post-contest,I found something which is the closest I can get to call 'logic'.So here it is :
    R9C1 is the 'total-cell' .7 is in one of R789C1 .If 8 were in R9C1 -->17 in R78C1-->35 in R9C23-->6 or 7 only in R9C9(which is the 'total-cell' in that box -->Both 6 and 7 totals are not possible in that row.

    This shows that 7 is in R9C1 and not 8.This sets the sudoku in its place ....

    1. I unlocked the fuzzy arrows in row 9, too, just a bit different thinking: you have 9 in R9C5, 2 in R9C6, the arrows in regions7 and 9 force the sum of R9C456 to be odd. Thus you have 2 possibilities: 6 or 8 in R9C4. 6 in R9C4 means R9C1+R9C9=14 which is not possible with 6 and 9 already placed.
      Thus R9C4=8, R9C1=7, R9C9=6, etc...

      Speaking about the hard classic, I would just be a bit less categorical than you. I don't have enough technique to use the XYZ wing to solve it, but I did a mental guess in this location to arrive at the same conclusion.
      That being said, I'm not sure that no player is able to solve it using the XYZ technique in a decent amount of time, so I leave the door open to this kind of classic sudoku, even if I prefer to see hard ones that requires less advanced technique. I agree the set of classic sudoku was not well balanced though.


  3. I struggled a lot on the Fuzzy Arrows during the competition, but I had a second look at it and found a path that was close enough to the one followed by Fred. I am still not completely sure what was intended and what was not, but at least it is good to know that it was possible to solve it in a reasonably clean way.

    About the hard classic, my view as a long-time amateur of tough classic sudokus is that it was not a great choice for a competition. Not that it could not be solved without guessing in a reasonable amount of time but in my eyes, guessing was clearly the fastest option there. I forced myself to search for a "fully logical" path because that is the way I enjoy, but there is no doubt I lost at least a couple minutes doing so. I don't mind having to look for moderately advanced techniques on a classic sudoku if spotting them is easy enough with minimal use of pencil marks, but in my opinion it was not really the case here. And obviously, the transition from four very easy puzzles to this tough one felt anything but smooth.

    As always, thank you for an interesting write-up, Tom.

    1. If you are consistently able to spot the "diabolical" techniques in less than 10 minutes then I am in awe! I am usually able to do so with the "tough" techniques (x-wings, swordfish, colouring, y-wing) - but beyond that I still struggle even without the time pressure.

      There was a moment where you could use uniqueness to make things a bit easier but even so, the techniques needed here were very hard.

  4. Not too much sympathy for me, Tom. I entered what I had in the scoring rows for the Fortress whilst knowing that there was a fortress error (just in case the fixing of that error wouldn't affect the scoring rows), but didn't expect to score for it. No idea what happened on the Diagonal, probably a transposition typo or similar.

    I quite liked this round. Lonely Number was so difficult for me I could largely ignore it, and the rest played to my strengths apart from Fortress. In general, as usual, I disagree with your assessments extensively, not so much about what was easy/hard but about what is fair to include. But then we are very different solvers.


  5. Hello!
    My reaction on "IB leaks" is in GP forum - there is no mystery and no conspiracy in what happened - it is not easy for me to accept that it is labeled as a severe violation.

    Here is our ratio for the "balancing of the competition" which was accepted by GP Director. (He asked similar questions at first.)
    "We think that 4 easy classics is a good move to please less experienced players. We would like to have one hard classics to teach players that variations are more fun than classics. And we think that Duodoku plays a role of the sixth, medium-hard classics. So if it is not necessary, I would not add a classic sudoku to the set." (a quote from the conversation with Nikola)

    Jan Novotny

    1. "Teach players that variations are more fun than classics" ???????????
      What a very weird statement !!! I can not believe what I read !!!
      Well, at least I can be happy that you didn't choose a variant which is hybrid with a non-sudoku puzzle to "teach sudoku players that non-sudoku puzzles are more fun than sudoku"...
      Please try to respect all players, even those who don't have the same preferences than you. There is nothing to teach in the subject "some puzzle types are more fun than others", and in no case it's a good idea to achieve this by creating a poor version of the type you don't like...

    2. I knew that I would regret that I contributed to this discussion...

    3. Jan, I was few months ago affected by one comment you wrote to me:
      "I am sad when somebody is building a wall with a barbed wire between sudoku and puzzles."

      Now I have the answer: YOU build such walls, not me !

      I spent more than 6 hours (~6 times more than for creating a sudoku) to try to create a decent fillomino for the puzzle GP, the harder task I had to do in my life as a puzzle author !
      I don't know if I achieved but I worked very hard with lot of respect to puzzle players.
      I didn't try to teach that fillomino is less fun than sudoku.

      What a disrespectful tought ! I'm shocked !

    4. Well, the following is most probably my last contribution into international online discussion about sudoku:

      It was a mistake to make an exact quote from an email to Nikola. Maybe it is not obvious what is 100% serious in it and what is not; or what is a poor selection from a limited english vocabulary.
      I think that Nikola understood well what I wanted to say and I am pretty confident that the final result of Jakub's, my and Nikola's work was a decent sudoku GP round. Not an excellent one to please all minorities, but hopefully a decent one to please the majority.
      I was satisfied with ourselves before I sank into this discussion.

      I am not competent enough in English to fight in online chats with people who don't like to understand just to catch the words.
      Also, I have no time to get upset about sudoku world, four more competitions with my contribution are coming in the next 3 weeks in Czech and Slovak Rep...

      PS1. Fred, the older quote about the wall was meant in general. I can't take a responsibility for the fact that you usurped it to you and only you.

      PS2. Yes, Fred, the most recent quote about people who don't try to understand me is not general, it is about you.

    5. Ok - I hope we can play nice and have a respectful discussion. This isn't life and death and I'm grateful for the work that Jan, Kuba and Nikola did to make this round possible. I'm also grateful to you Jan for sharing your thoughts here

      Yes I have plenty of opinions about how things are, and that's fine, but I also have an opinion that having a competition is better than having no competition at all!

  6. The sixth classic in GP was always guessy so I would like to thank Tom the 2016 season was different in this regard. I use minimum pencilmarks so it is hard for me to find these chains but I agree with Fred that it is possible some players are more efficient in finding logical steps in these spots. My suggestion is that if you want to test players´ ability to use advanced techniques, Just One Cell Sudoku is a better option since it completely eliminates guessing.

    As for the Fuzzy Arrows, I started in box 1. The minimal sum on the arrows is 16 (1456) and from 1456 you can´t make two eights. So r1c1 must be 9 consisting of 18 and 45. It forces 9 to r2c7 and 7 to r3c2. The 7 in box 3 must be on the arrow so r1c9 can only be 7 or 8. Then you can´t place 4 to r1c78 so in the first row it must be in r1c2. Then you can continue in box 7.

    I wasted a lot of time on Pointing Differents. I kept arriving at a solution that had 4 different digits instead of 5 on one of the arrows. I actually started thinking the puzzle was broken. It made me feel discomfortable since it was the first puzzle I was solving (except the first page of classics of course). I managed to find the correct solution couple minutes before the limit so I had some more time to stare at Lonely Number Sudoku again. As usually I noticed the gimmick a few seconds after the time was over.

  7. Thanks all for commenting, it's really interesting to see how other people found this round, and it's really great to hear how other people solved the puzzles. I'll be really happy if i can continue to get anything like as good a discussion for the other rounds.


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