April 11, 2017

2017 Sudoku GP: Round 4 United Kingdom

First off - the last couple of weeks of Friday Puzzles have been delayed for one reason or another.  Hopefully I can catch back up this week and post 3 puzzles this coming Friday.

Secondly, although I have been quite free with my opinions about this year's Sudoku GP thus far, if you think I have the temerity to rate my own puzzles - then you have another thing coming, dearest reader.  Nevertheless, I thought it'd be worth offering an author's (rather than ex-director's) view on this round's puzzles, which I co-authored with my good friend/bitter solving rival, David McNeill.

1-6 Classic Sudoku (25, 17, 20, 25, 47, 30 points)

So I hope this represented a decent selection of classics.  Certainly no puzzle was what I'd call a guessing puzzle.  David's were puzzle 2 and 6, the rest were mine.  Puzzle 1 is probably a lot easier if you start by placing all the 1s, then the 2s and so on.  This is a standard nikoli gimmick for easy puzzles that I like to throw out every now and again.  It works better if you aren't necessarily expecting it; over using it wears thin very quickly.  5 was the hardest, perhaps notable because it needed a few naked singles to get going.

7 Diagonal Sudoku (31 points)

David's puzzle - not sure there's too much to say other than a pleasant enough Diagonal puzzle

8 Antidiagonal Sudoku (33 points)

Mine (and I prefer Anti-Diagonal) - This was nearly a very good puzzle of 16 givens, but I couldn't quite get it to solve uniquely.  I'd have persisted with this a lot longer had this been say, for a world championships.  This would have fitted in well with a couple of other 16 given puzzles in Round 2 of the 2014 WSC, and might be something I end up revisiting.  Watch this space.

9 Windoku (58 points)

Mine - I really quite like Windoku as a type, with its 4 visible extra regions and additional 5 implied extra regions.  At first glance you might think I was going for another 16 digit puzzle and had to add another given in the middle to get to 17, but no, that's not what I was going for this time.  Perhaps the more observant of you will have noticed the centre 9 givens form a magic square?  Anyhow, a reasonably tough windoku, as far as these things go, but I suppose if you've done a few of my puzzles you'll have got through this steadily enough.

10 Antiknight Sudoku (36 points)

David's (and I prefer Anti-Knight) - I suspect he was going for a 17 given puzzle here and had to add the corner givens to get this out uniquely.  Other than that, a pleasant enough Anti-Knight solve.

11 Disjoint Groups Sudoku (56 points)

David's - I always think that half the issue with disjoint groups sudoku on paper is visualising each of the 9 disjoint groups.  When solving I often have to draw shapes in the cells to help with that.  This puzzle has a nice UK theme, and is potentially a tricky solve if you struggle to visualise the groups, but if you are comfortable with the type I think solves quite nicely.

12 Irregular Sudoku (40 points)

David's - the temptation with nicely designed irregular puzzles is to push the difficulty to an extreme, or else to go to extremes using the grid's geometry to shape the solve.  I think David hit a nice medium here - the first comment I gave when testing this was that I assumed a couple of the givens weren't strictly needed (in the sense that removing them would still give a puzzle that solved uniquely) and that it felt like an easy solve - but checking my time it was clear that this wasn't a trivial puzzle and instead the feeling that it had gone quicker is a reflection on how nicely the puzzle solved.

13 Renban Killer Sudoku (63 points)

David's - normally I'm sceptical about combining together too many rules, but the combination of Renban groups and Killer cages combines really nicely and I think David is really on to something with this variant, which he has made his own.  Another nice example

14 Cloned Strands Sudoku (33 points)

David's - I'm pretty sure David invented this type primarily to draw funny pictures of animals.  And a nice illustration that novelties don't have to (a) have overly complicated rules and (b) have overly difficult solving logic.

15 Total Blackout Sudoku (86 points)

David's - blackouts tend to have quite fiddly solving paths, so the gimmick with the sums of the cells around the cells helps to give this type a bit more flavour, as well as providing a nice pun for the variant.  I think most of the points value here comes from firstly the novelty value of the variant, and second of all the slightly fiddly bit of logic needed to resolve the top right of the grid.

Top 3 (preliminary results):
1. Kota Morinishi (850.3 points)
2. Tantan Dai (845.5)
3. Tiit Vunk (790.2)
It looks as if there is a strange result for 11th (Huxuan Yu) who has a lower points total than 10th, despite the fact he managed to solve the puzzles nearly 3 and half minutes faster, going by submission time.  It's my strong suspicion that this is another case of the failure of the claim bonus button, an issue that has been plaguing the GP for years, particularly for Chinese solvers.  I hope an appeal is made or someone notices this before the results are made final.

As for the Brits:
45. Heather Golding (478)
68. Mark Goodliffe (380)
99. Michael Collins (334)
Also good to see there was a relative strong UK turnout of 18

March 24, 2017

Friday Puzzles #298

I've run out of time to add the final polish, but there should still be enough here to keep you busy.  Cages are clued with the sums of numbers to be placed inside them; no repeats within cages.

    #339 Killer Sudoku – rated medium
All puzzles © Tom Collyer 2009-17.

March 17, 2017

Friday Puzzles #297

Non-Consecutive Sudoku this week.  Cells that share an edge are not allowed to contain consecutive numbers.

    #338 Non-Consecutive Sudoku – rated medium
All puzzles © Tom Collyer 2009-17.

March 14, 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).

March 10, 2017

Friday Puzzles #296

Odd sudoku this week.  Only odd numbers are allowed in the shaded cells.

    #337 Odd Sudoku – rated medium
All puzzles © Tom Collyer 2009-17.