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