2017 Sudoku GP: Round 2 France

Ok, so this was the Bastien Vial-Jaime show.  Having known this I was very confident this would end up have the highest quality puzzles of the entire series - and having now solved them I think this is very like to end up beingtrue.  If there's a better author around than Bastien then I certainly don't know them - his variants are always fresh and innovative, and the classics he writes always solve beautifully.

Nevertheless this round wasn't as fun as round 1 for me, for reasons that have more to do with myself rather than the puzzles themselves.  Very often the clever tricks to the puzzles were lost on me and given the time pressure I had to do a bit of bifurcation (to resurrect my favourite euphemism) to get the puzzles out.  Also there was a Fortress Sudoku which inevitably I cocked up.  It seems to be the rarest of Fortress Sudoku in competitions that I do not break.  For what it's all worth, here are the vital stats for the round:

Enjoyment: 6/10

Classics: 9/10
Favourite Puzzle: Killer Sudoku

So onto the review.  First thing I'll note is something that I didn't notice last time, but which I did this time.  Round 1 the shade of grey was definitely too dark.  For this round we are back on track with an acceptably light grey.  The difference this makes to solving should not be underestimated!

1-5 Classic Sudoku (21, 17, 28, 20, 41 Points)

This being the first page out of the printer, I went straight to the classics.  All in all, they were very high standard, with strong distinctive visual patterns of givens that weren't constrained to the traditional 180 degree clue symmetry and in each case guided by clear and smooth solving paths that weren't trivial even for the easiest puzzles.  I only knocked off a mark here because I'd have liked to have seen another ~40 point puzzle included -- ideally in place of the Almost Palindrome?

6 Diagonal Sudoku (72 points)

A beautiful puzzle that would have been my favourite puzzle on any other round.  Nearly minimal in terms of givens, with a mere 17, they were all populated in the top half of the grid.  This meant that the solve elegantly cascaded down through the grid.

From a presentational point of view, I'm pretty much converted to having solid diagonal lines rather than dashes.

7 Figures Sudoku (66 points)

I had this and an attempt to retry the Fortress with 7 minutes to go, and failed miserably. I tweaked that the figures might actually be extra regions, and used this as a half hearted attempt to get it out in time, but I wasn't successful.  It'd be interesting to actually deduce the logic for this some other time as I can't see how you make any progress without realising this. The other note here is that the cages for this puzzle were formatted differently from the cages for Killer Sudoku, which irritated me a little.

8 Fortress Sudoku (58 points)

As with many other competition Fortress Sudoku puzzles, this was going very well until suddenly I hit a big contradiction.  My attempts to fix this in the last 7 minutes were sadly fruitless.  What was doubly annoying was that I caught myself making a false assumption early on in the solve.  What would be triply annoying would be when I do go back to solve this, it may well turn out this falsely made assumption may have nevertheless not contradicted the final solution.  Ugh.  For what it's worth this felt like it was another excellent puzzle.

9 Renban Groups Sudoku (64 points)

Perhaps I'm being a bit precious on this one, but I don't really like to see this abbreviated simply as "Renban Sudoku".  I corrected this without comment for Round 1, but there, I've made this very minor point here!

Semantics aside, this was a lovely puzzle and probably a candidate for favourite puzzle on another round.  I did have to accelerate progress with this one with a well chosen bifurcation, which admittedly does take something away from the competition experience (for me anyway).

10 Thermo Sudoku (36 points)

A striking design that solved cleanly and elegantly, another excellent puzzle.

11 Killer Sudoku (84 points)

Every now again I come across a Killer that I start raving about, and this is one of them.  I think I just really like it when the interplay between no repeats in cages and the addition really comes off - you can get a similar thing with extra regions/consecutive with Renban Groups but in my opinion there's an extra layer of solving richness with addition.  

This was perhaps slightly tarnished in competition as I had to bifurcate to get myself started which meant that again I missed something, but the bits I did get were enough to confirm to me this was a thing of real beauty.  

I think this is probably one of those puzzles that I might have umm-ed and ahh-ed about including before ultimately liking it too much to throw away, nevertheless I would have to accept this isn't necessarily the same kind of Killer that many less experienced solvers are used to.

12 Odd-Even Pairs Sudoku (56 points)

This variant has been around with various names and various presentation, and I think in general whilst I like the name here, I'm not so keen on the use of "capsules" as a presentation.  I think I'd prefer to see the shaded Renban Groups style here instead, assuming you really wanted to make the cells prominent - or else to stick with the (more) standard "Pairs" style marking of a circle between the two adjacent cells.

That all said, the capsules style presentation for this puzzle did make the puzzle's defining gimmick much easier to spot (i.e. that you had to have odd numbers in R3C3 R3C4 R4C3 and R4C4) and the puzzle again solved cleanly and elegantly after that.  Another excellent puzzle!

13 Almost Palindrome Sudoku (37 points)

I'm not hugely keen on these "liar" or "almost" constraints in general, and although this one solved nicely enough it's definitely one where the constraint was in parallel with the sudoku solving rather than then augmenting it.  A good example of where it does work is with Surplus or Deficit Sudoku.  That's just my personal preference, but I don't think this one quite reached the exceptional heights of the rest of the round.

So, 11/13 solved (still no mistakes!), but I didn't feel like I was close to finishing this one, which I think also takes away a little of the enjoyment from solving.  I suppose the proof will be in the results, but I suspect this will be perhaps quite a bruising experience for less experienced solvers, and one where experienced solvers really need to be on top form to come away happy.  

It feels a bit strange to say that perhaps there were too many "clever" puzzles for a competition, but with the clock ticking away I did have to rely on bifurcation more than I'd have hoped and I'd be interested to hear whether this was the same for other solvers.

Having initially written most of this post on Sunday, and having now seen the results, it looks like my gut feeling was pretty close to the mark.

Top 3 (preliminary results)

1. Shiyu Chen (795.7 points)
2. Tiit Vunk (761 points)
3. Jakub Ondrousek (692.2)

A new name for me is Nicholas Ling of Australia, finishing in 16th place, which would be pretty impressive going for a newcomer.

And for the Brits:

27. Tom Collyer (476)
53. Heather Golding (372)
71. Mark Goodliffe (325)

Well done Neil for having a go!

Friday Puzzles #292

Can you tell what it is yet?  Small packages can still sometimes pack a punch!

1 to 7 once in each row and column, and at most once in each 6 cell region.  Enjoy!

    #333 Deficit Sudoku – rated hard

(A fixed version of a previous puzzle)

All puzzles © Tom Collyer 2009-17.

Friday Puzzles #291

Well this would have been on time if my laptop hadn't given up the ghost.  How irritating.

1-7 once in each row and column, and at least once in each 8 cell region.  Enjoy!

   #332 Surplus Sudoku – rated medium

All puzzles © Tom Collyer 2009-17.

Friday Puzzles #290

So I think for 2017 this blog may well be just sudoku and variants - however I will be posting links to Grandmaster Puzzles as and when my puzzles there get published.

Lets see how it goes, dearest reader.  As ever, hope you enjoy!

    #331 Sudoku – rated easy

All puzzles © Tom Collyer 2009-17.

2017 Sudoku GP: Round 1, Netherlands

Last year (2016) I was in charge of the WPF's Sudoku GP series, which was a very interesting and exhausting experience.  This year, I've taken a step back and am able to enjoy competing in the competition.

My first impressions involve a little disappointment in the downgrade of publication quality - the competition is no longer published using vector graphics, and the typeface has been changed from Helvetica to Arial.  The changes are minor and the untrained eye is unlikely to notice any difference, but the major gridlines seemed much too thick to me, especially in comparison with the width of the printed givens, which is unfortunate because the givens do not stand out as much as they should.

Minor gridlines cannot be any thinner than a pixel if the graphics are not in vector form (although you can kind of approximate by colouring them grey rather than black), which is unfortunate as this is a big limitation on the ratio of major to minor gridlines.  This is a very important ratio in the aesthetic of a sudoku grid!

EDIT: This is not quite true - whilst the entirety of the IB is definitely not vector format, the CB puzzle grids do seem to be vector format (although bizarrely the text in the CB is not...).  In any case the thickness of both minor and major gridlines has increased, which is ultimately the point I am trying to make.

With regards to the differences between Arial and Helvetica: they are minimal, but the former is a piss poor imitation of the latter when it comes to R's, G's and (most relevant to a Sudoku grid) 1's.  The Arial 1 is a nasty piece of work.  There, I've said it!

All that said, I also know how much work goes into producing work of publication standard.  The director's first responsibility is there puzzles - it's a nice bonus if the director also has skills in the area of publication, but otherwise this is all work for a separate role which hopefully the WPF can sort out.  From this point I suppose I will try and leave any further comment on publishing unless it it directly impacts the solving experience.

So, on to the puzzles themselves.  Round 1 of the GP is normally organised in a bit of a rush, particularly if there is a new director settling into the job, so it is great to have reliable hands like Richard Stolk and Arvid Baars who can step up and produce a high quality round at reasonably short notice.

From a personal solving point of view, I've historically not fared too well with Richard's puzzles in competition, but I've now also solved a lot of his puzzles and I think I'm getting better.  I was therefore optimistic about having a good round and generally getting back to solving at a high standard.

1-6 Classic Sudoku (12, 29, 27, 36, 49, 22 points)

I solved the first four to ease myself into the competition, and they all seemed nice enough.  The 5th I came back to a bit later, which was definitely the hardest of the set but pleasingly not at a guessing level.  The 6th I had 3 minutes to solve at the end of the round, and rather frustratingly didn't get out in time.  Not sure there's too much more to be said about the classics other than they were at the reliably good standard I've come to expect from those two.

7 Clone Sudoku (21 points)

This was easy as the points total suggested, however I cocked this up during the 90 minutes and didn't have time to come back to the fresh copy I printed off.  As the mistake came quite early in the 90 minutes this may have thrown me off a bit.

8 Renban Groups Sudoku (47 points)

A reasonably tricky puzzle which I got half way through before setting aside and only came back to much later in the 90 minutes.  There was some nice logic determining what a few of the Renban groups were by noting the possible min and max values for the groups

9 Sudoku XV (23 points)

It's a bit annoying that XV Sudoku has suddenly become Sudoku XV, but it was definitely annoying that I managed to cock up another easy puzzle without having time to come back to it in the 90.

10 Consecutive Sudoku (64 points)

Very striking given consecutive bars - usually when you have something like this the non consecutive constraint becomes even more important, which makes for a bit of a fiddly solve.  This puzzle was a bit like that - a little hard to get in to, which reflects the high points value but once you were the overpowering non-consecutive constraint took over.  I suppose puzzles like these are why given the choice I prefer Consecutive Pairs, where the converse rule is not in place.

A quick note here on the instructions for this puzzle:

Apply classic sudoku rules.  In all cases where two neighbouring cells contain consecutive digits, a grey bar is placed between those cells.

This is more concise and compact than rules I've written, and the reason for this is because it is not immediately clear to a beginner what the "all" is implying (i.e. that a non-consecutive converse is also in effect).  This is dangerous for a puzzle like this that is ultimately dominated by the non-consecutive constraint - it is easy enough to satisfy the grey bars and then arbitrarily fill out the rest of the grid without quite being sure why such an answer is incorrect.

As another matter of taste, I much prefer to refer to placing numbers rather than digits.  This way you can reserve the term digits for variations which make use of strings of placed numbers.  Placing numbers is also a nod towards an early name for Sudoku, which was of course "Number Place".

11 No Touch Sudoku (41 points)

Easy enough, but common to this variation its often easy to miss the one thing you need to make progress in the puzzle.  This probably took me too long to solve.

12 MaxAscending Sudoku (69 points)

A novelty to me, a cute idea but perhaps not a variant with much staying power once a few gimmicks have been explored.  This seemed to solve relatively nicely given the high points tally.  I'm not quite sure why this isn't "Max Ascending" with a space.

13 Mathrax Sudoku (56 points)

A Richard/Arvid specialty.  Both are capable of making this variant really quite tricky, but this one was a little friendlier and didn't cause me too much of a problem.

14 Scattered X-Sums Sudoku (53 points)

X-Sums in an irregular grid is nothing new, and the scattered grid is only a mild relaxation of irregular regions so I don't really count this as a novelty.  The overly thick major gridlines provided sufficient contrast with the (overly thick) minor gridlines - I suspect I'd have been quite annoyed if there were givens in the grid being visually overpowered - but there weren't and it solved quite nicely.  Probably took longer than it should have, and there was a brief moment at the end where I thought I had another cock up.  Luckily for me I was able to fix it.

15 Unique Order Sums Sudoku (51 points)

I think I've possibly seen this (or something similar) as a Daily League puzzle in previous years, but this is likely to be novel to most.  I didn't think I'd be a big fan of this based on the pig of an example in the IB.  Perhaps it's a little too puzzle-y for some tastes, but the observation that there are only 15 unique sums of 2 digits means that it's potentially very quick to ascertain the value of the 12 ordered cages and then solve very quickly as an easy Killer Sudoku.  This was the only puzzle I didn't look at in the 90 minutes at all, which is a shame as I'm pretty sure I got it out in the 3 minutes I had at the end.

Overall a nicely balanced set, one which I think I might have finished on a good day, but on this day I managed 11/15, scoring 483/600 points.  No submission errors is definitely a positive for me!

Enjoyment: 8/10
Classics: 8/10
Favourite Puzzle: Renban Groups Sudoku

Top 3 Overall are (results are preliminary at the time of writing):

1. Tiit Vunk (855 points)
2. Jakub Ondrousek (853.7)
3. Seungjae Kwak (817.8)

Also good to see a return to competition from my GM Puzzles colleague, Thomas Snyder in a very creditable 4th.  The competition at the top will certainly be fierce this year.

Top 3 UK:

47. Tom Collyer (483)
66. Mark Goodliffe (424)
67. Heather Golding (423)

I suspect the UK top 3 will be a permutation of these three names, bearing in mind David McNeill isn't participating, and Neil Zussman is just plain lazy.  I would love to be proved wrong and have a UK newcomer come to shake things up!