Sunday, 25 June 2017

Blog Update

So a couple of things have happened over the last couple of days.  Most importantly on the typography front, I've decided Times New Roman makes for lovely display, and that there are some acceptable other typefaces languishing in the google font foundry.

I'm rearranging other content from the blog as best I can, and there might even by the odd new tit-bit here or there.  For example my PhD thesis!  I'm also experimenting with the "jump break" feature.  At first glance this looks as if it might be immensely irritating to my dearest readers, but I also appreciate that I sometimes waffle on insufferably and this might give people a chance to navigate these choppy waters.

Thursday, 15 June 2017

2017 Sudoku GP: Round 6 Serbia

A couple of weekends ago, a few nutjobs got a bit stabby in the London Bridge area of London - an area that is about half a mile from where I live.  I don't want to give them any coverage in particular, but what with everything going on I completely forgot to take part in round 6 of the Sudoku GP, "hosted" (I'm not sure that's exactly the right word) by Serbia.

I've gone away and solved the puzzles, not quite under time pressure as I got interrupted towards the end.  Nevertheless, I've done a review:

Enjoyment: N/A (doesn't seem appropriate without the full competition experience)
Classics: 6/10
Favourite Puzzle: Dead or Alive Arrows Sudoku

Unfortunately missing this round means I've hit a 0 for writing the UK round, and a 0 for this round, so everything else is going to count.  I really need a good couple of last rounds - I suspect the final UK reckoning is going to be very tight between Heather, Mark and myself.

Friday, 26 May 2017

Friday Puzzles #301

Skyscrapers Sudoku this week.  (I haven't got around to my backlog yet).  Numbers represent heights of buildings, where bigger numbers block smaller numbers.  Clues outside the grid indicate how many different buildings are visible.


Edit: previous version had an error.  Hopefully that's fixed now.
    #342 Skyscrapers Sudoku – rated medium
All puzzles © Tom Collyer 2009-17.

Friday, 12 May 2017

Friday Puzzles #300

How appropriate to celebrate a nice round number by being nearly-but-not-quite late!

Clues outside the grid indicate the "property" of the first two numbers placed in the corresponding direction.  Odd=1,3,5,7; Even=2,4,6,8; Big=5,6,7,8; Small=1,2,3,4.

    #341 Odd-Even-Big-Small Sudoku – rated medium
All puzzles © Tom Collyer 2009-17.

Tuesday, 9 May 2017

2017 Sudoku GP: Round 5 Estonia

So hopefully there will be no further barrage of comments this time round, nothing too controversial going on here! The authors this time round were the world champion, Tiit Vunk, and Rauno Parnits. I can't personally recall any more than the occasional puzzle from either author, but this time round there was a pretty heavy chess theme to the round. And although a theme is nice to have, more important in my eyes is a good solid set of fun puzzles to solve, and that's what we got with this set. The vital stats according to me were:

Enjoyment: 7/10
Classics: 7/10
Favourite Puzzle: Chess Kings Sudoku

Anyhow, on to the review.

1-6 Classic Sudoku (18, 20, 16, 43, 20, 40 points)
I tend to like the classics being arranged in the order of difficulty, but I suppose the gimmick here were the patterns of givens, which were respectively a King, Queen, Rook, and a Bishop. This was followed by "b1c3" which I don't quite get (a Knight's opening?), and then "1/2" which I suppose is a draw. Nothing particularly difficult, nothing overly easy (despite some fairly low points totals) - I think the last one had some colouring going but generally a solid set of classics

7 Diagonal Sudoku (43 Points)
Another bishop shaped set of givens, I suppose this makes a lot of sense for a Diagonal puzzle.

8 Fortress Sudoku (39 points)
One of my favourite Fortress puzzles of recent memory. I don't much like the type, but this was remarkable firstly for (1) the clever use of a checkerboard pattern as the fortress with row numbering to the side, and (2) solving cleanly without me making a stupid mistake.

Scratch that, it's another fortress puzzle I've cocked up. This is utterly bizarre.  I need to go away and practice these for a week until I stop cocking them up.

9 Queen Sudoku (69 points)
I definitely prefer the plural "Queens". This was nice enough for the points, but I do think this type suffers a little bit because as soon as you try and make one with any kind of difficulty it's very tempting just to guess the placement of the queens. The non-attacking constraint is pretty strong, which pretty much guarantees a quick contradiction if you happen to make a bad guess, and easy enough to double check if you make a good guess sans contradiction. Which I did.

10 Battenburg Sudoku (73 points)
Nice to see this type make an appearance. This is generally quite a puzzle-y type as the key to solving these is by first determining whether a particular cell contains an odd or even placement, with the converse rule also needing to be used heavily to make any headway.

I am not a fan of the phrasing "all such patterns are marked".  I think it is far more friendlier to newer solvers to explicitly say "where there is no marking, there can be no pattern".  It feels like I'm banging the same old drum here, but really we do ourselves no favours as a community when we make things harder than they need to be.

11 Antiknight Sudoku (85 points)
I made the strategic error of leaving this puzzle until last, and my placing suffered massively for it.  It didn't feel particularly remarkable to me, just a tough version of a type I personally don't enjoy all that much.

12 Sum 10 Twin Sudoku (37 points)
Well done me for solving this without submitting an answer.  An otherwise pleasant clone style variant.

13 Chess Kings Sudoku (44 points)
My favourite of the round, and a surprisingly elegant extension of the "No Touch" variant.  The example for this novelty had the gimmick that you could isolate the pair of kings by considering the centres of the 3x3 boxes.  This logic left me with 1,3,4,7,8 as the possible kings, and although this still leaves a possible 10 different pairs, actually these were eliminated almost instantly leaving the rest of the puzzle to solve nicely.

14 Unicorn Sudoku (53 points)
The constraint feels very very strong for this novelty, and I only used it around three of the placed 9's to solve the puzzle.  I think it's probably stretching the chess theme a little thinly, and I don't think we'll see too many more of this type, but it solved pleasantly enough.

I had to take this test last on Monday in a bit of a rush, and my solving performance was down.  It definitely wasn't helped by not submitting an answer to one of the puzzles.  The preliminary results have now been released and it does looks like there have been a fair few mistakes.  I ended up with 12/14 puzzles correctly solved, 11 submitted, 1 stupid error, and perhaps a couple of minutes extra required to finish the anti-knight.

Despite a disappointing result, and a mix of variants which aren't necessarily to my advantage, I did enjoy this round a lot, and hope that the remaining rounds can match this standard.

Top 3 (preliminary results):
1. Jakub Ondrousek (882.8 points)
2. Jan Mrozowski (872.3)
3. Sinchai Rungsangrattanakul (847.7)
I had to scroll down much further than I cared for to find my result, and I was surprised to see that I was just two places behind Dr. Snyder, who had 2 errors costing over 25% of the points plus bonus.  I suppose I shouldn't complain too much.  Commiserations also to Tantan Dai, who informed me of further computer problems which meant her initial submission of under one hour (a score in excess of 900) was not received by the server.  Even then, re-submitting the answers via tapping them out on a mobile phone in an extra 10 minutes was still good for an incredible 6th place, and the current overall lead of the GP (see the link below).

As for the Brits:
35. Mark Goodliffe (561)
51. Heather Golding (483)
68. Tom Collyer (439)
Submitting my extra puzzle would have pushed me to 476 points, and 54th place, highlighting the magnitude of the blunder of leaving the anti-knight until last.  Mark's performance is the best British score in any of the rounds this year, and represents a really strong solve - congratulations!

What is definitely interesting is this page - which highlights that Mark and Heather are separated by a single point over 5 rounds.  Granted the dropping of the two worst scoring rounds will start coming into play here, but it's fascinating to see who will come out on top here.

I'm pretty confident I'm going to need to score bonus time on at least 2 of the remaining 3 rounds if I'm going to end up where I'd set my eyes upon at the start of the season.  I'm not sure this is looking very likely at the moment!

Friday, 5 May 2017

Friday Puzzles #299

I've got a backlog of puzzles that will hopefully be unleashed either later today or else next week.

This one is x-sums.  The clues outside the grid indicate the sum of the first X placed numbers in the corresponding direction.

So for example a clue of 6 could have X=2, in which case the second placed number would have to be 4.  Or, it could have X=3, in which case the second and third placed numbers would have be to 1 and 2 in some order.

    #340 X-Sums Sudoku – rated easy
All puzzles © Tom Collyer 2009-17.

Tuesday, 11 April 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

Friday, 24 March 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.

Friday, 17 March 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.

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).

Friday, 10 March 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.

Friday, 3 March 2017

Friday Puzzles #295

The difficulty this week is turned down a little.  Enjoy!
    #336 Windoku – rated medium
All puzzles © Tom Collyer 2009-17.

Friday, 24 February 2017

Friday Puzzles #294

This one is fairly tricky too.  Enjoy!
   #335 Diagonal Sudoku – rated hard
All puzzles © Tom Collyer 2009-17.

Saturday, 18 February 2017

Friday Puzzles #293

Yes it's not Friday any more.  This should keep you busy for a while!
   #334 Irregular Sudoku – rated hard
All puzzles © Tom Collyer 2009-17.

Monday, 13 February 2017

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, 10 February 2017

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.

Saturday, 4 February 2017

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, 27 January 2017

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.

Thursday, 19 January 2017

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!

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