Friday, 31 December 2010

Friday Puzzles #85

Well, as we bring 2010 to end, dearest reader, I must confess that this post has been written in advance, as I am currently having almost literally a whale of a time in Berlin. I’m afraid that means that there isn’t going to be a puzzle here until sometime next week – I have had myself a nice and lazy and indulgent Christmas break at home with the family.

However I hope that everyone has enjoyed my offerings this year, be it my rather manic 7 puzzles in 7 days which heralded me branching out to writing a few new puzzle types; or perhaps my long Championship write-ups from Philadelphia in April and London in September; or the start of my “career” as a competition writer with both the (moderately disastrous) LMI Nikoli Selection and the UKPA Sudoku Championship (well done again Warren!); or perhaps one of the numerous twisted symmetry Masyu I always seem to resort to when I’ve forgotten to write a puzzle for a particular week.

Anyhow, I hope everyone has had a good 2010, and here’s to the promise of 2011 – not least the puzzle that’ll be edited in here later!

EDIT: Here as promised is the puzzle. I will probably be revising Heyawake fairly soon, in response to an email I had from Otto Janko before Christmas – but for now, here is a nice small puzzle which should prove a bit of a tough nut to crack. Enjoy!
    #111 Heyawake – rated hard
 
All puzzles © Tom Collyer 2009-11

Friday, 24 December 2010

Friday Puzzles #84

Happy Christmas, dearest reader!

I nearly forgot to put out a post – just like the good old days – but luckily enough there was something lurking at the bottom of the pile in my “unpublished” folder.

And with good reason too.

Christmas is an occasion the newspapers like to fill with bumper sized crosswords, and extra hard sudoku puzzles, and other puzzling novelties given that we have all this spare time on our hands. The thing with this puzzle is it’s much harder than that. Enjoy!
    #110 Sudoku – rated hard
 
All puzzles © Tom Collyer 2009-10

Friday, 17 December 2010

Friday Puzzles #83

Busy busy busy this week, so here’s a Masyu with relatively few clues – 15. To spark a debate, has anyone seen less? I can’t recall one off the top of my head this second as I provocatively write this statement…
Anyhow, enjoy!
    #109 Masyu – rated easy
 
All puzzles © Tom Collyer 2009-10

Friday, 10 December 2010

Friday Puzzles #82

I’m afraid I’ve been in Galway all week, sans laptop, and so you’ll have to wait until at least Monday before I edit something in over this!

UPDATE:

So I have a little folder of odds and ends on my laptop entitled “unpublished”. In it, I found this rather pleasing looking sudoku puzzle. I haven’t had a look at it for a long while, so I can’t totally vouch for it being an easy, but it seems unlikely that I’ve stitched together a decently challenging sudoku that looks this good. Enjoy!
    #108 Sudoku – rated easy
 
All puzzles © Tom Collyer 2009-10

Friday, 3 December 2010

Friday Puzzles #81

First up – I’ll post this week’s puzzle – which is a fairly gentle nurikabe. It’s been a while since I had a nice and easy puzzle so I hope this pleases the more casual of my readers!
    #107 Nurikabe – rated easy
 
All puzzles © Tom Collyer 2009-10



But let’s move on. I want to discuss the numberlink puzzles from last week, and in particular make a few remarks about uniqueness of puzzle. As regular readers know, my approach to numberlink uniqueness is to find a solution to given array of clues and then try and establish its rigidity.
The first puzzle I’ll discuss is #106. Here is the solution:


The first intuition I have about numberlink rigidity is the idea of “unnecessary wrapping”. The general idea is to suppose you have a pair of clues A, and another pair of clues B – and draw the straight line between these two clues. If these two straight lines intersect, then it is clear that one of the solution lines joining the clue must wrap around the other solution line. Conversely, alarm bells should be ringing with any candidate solution if the straight lines are disjoint and yet one solution line wraps round the other.

It is a quick check with this puzzle to see that there is no such unnecessary wrapping. I haven’t rigorously proved to myself that this means the solution must be rigid, but I’d be very surprised if this wasn’t the case (with a few highly symmetric exceptions). Ok, fine, I haven’t got anything more to add to this at the moment so let’s move on.

Here’s what I had in mind (in black) with the original #105 I posted, together with (in red) where things go wrong:



So there are a couple of points to consider here. Firstly, look at that pair of 2’s, and the amount of what I’ve just defined as “unnecessary wrapping” it does! There’s something more than meets the eye going on here. The initial idea for the break-in to this puzzle was with the 1’s and the 5’s. A little spatial reasoning quickly suggests that one of the solution lines must go via the top-left of the grid, and the other along the bottom edge – so that the cluster of 3/4/6/7 is avoided.

A little more inspection reveals that the 1’s would be causing all sorts of difficulty with the 6’s if it went out top left, so the 5 goes round the top left. It was here that I made the mistake. I thought there was only one way for the 5 to get past the 4 and the 6, but completely overlooked the obvious route as marked in red. This was how I fixed the puzzle – by closing up the gap (and adding a 13th pair of clues):


This alteration made the puzzle a little easier than intended. The 3/4/6/7/13 are now essentially forced. A by product of this is that it forces the 2 to squeeze the “wrong” side of the 1. This is a bit of “logic” that only came in to play later in the original – but essentially reveals the origin of the “unnecessary wrapping” of the 2. The given clues in the puzzle are acting as blocks to the paths, which must channel in between them, with the obvious restriction that there are only so many paths that can fit into a small space. So once the 2 goes round the back of the 1, it also has to go round the back of the 8 and the 9.

The rest of the puzzle is then fairly trivial.

What I find interesting with this puzzle is that actually it wasn’t too hard to find a sketch framework to logically prove the solution is the only one. Ok, I’ll hold my hands up with the stupid oversight with the 5’s, but the fix was essentially minimal and still retains most of the features I wanted from the original puzzle.

Going back to #106, I think this one is much harder to make a start to the puzzle and go step by step in trying to establish forced paths. Instead, it isn’t too tricky to use a little metalogic (i.e. assuming uniqueness of the solution) to get the solution out – and then to do a quick check to see that this solution turns out to be rigid. Which is a completely different approach to things!

Anyhow, for all those numberlink fans out there, I hope this has provided a little food for thought.

Friday, 26 November 2010

Friday Puzzles #80

More Numberlink this week. Over the week I’ve pretty much convinced myself the solutions I have in mind really are the only ones, and I’ll go into this more maybe with an edit to this post in a few days. What I’ll say for now is this. I reckon the second is a much nicer puzzle than the first, but the first was definitely more easy for me to convince myself of uniqueness.

This seemed rather strange to me on second inspection, as it turns out that it has a few properties that I had previously thought might have been barriers to uniqueness. In particular, it fails a test I’ve devised to check whether if you have one solution, then you can only have one.

This test was something I came up with when inspecting the second puzzle again. I haven’t rigorously proved this to myself but it does make intuitive sense. The second puzzle does pass this test.

Anyhow, my apologies for being so cryptic – but be assured dearest reader that I am only because I don’t want to spoil the solving experience, and also with the promise of explaining all in a few days time. Until then, enjoy!

UPDATE (II): PUZZLE 105 EARLIER CAME WITH A SPECIAL OFFER OF MANY POSSIBLE SOLUTIONS FOR THE PRICE OF ONE!!!
    #105 Numberlink – rated easy
 

    #106 Numberlink – rated medium
 
All puzzles © Tom Collyer 2009-10

Friday, 19 November 2010

Friday Puzzles #79

We’ve not had a Nurikabe puzzle for a while. I claim this is a medium, but it might really be a hard. The reason for this is that the solving path is logical enough and I don’t want to be putting off some of my readers who do love a good Nurikabe put don’t want to dip their toes into a “hard” puzzle. Give it a bit of perseverance and you will get there in the end…

Anyhow, not the worst puzzle I’ve ever done, and perhaps this was indeed the right outlet after my rather rushed talk on Wednesday. Enjoy!
    #104 Nurikabe – rated medium
 
All puzzles © Tom Collyer 2009-10

Saturday, 13 November 2010

Friday Puzzles #78

Yes I post this entirely shamelessly, offering the fine excuse that yesterday I was rather busy having lunch and dinner in Oxford. There was a maths conference there too at some point, I think.

Anyhow, please believe me when I say that I really can’t keep this up forever. After this week I’ll give Masyu a break for a while. I can’t really compete with the Juno standard anyway. But this isn’t bad :)
    #101 Masyu – rated medium
I’m also going to repost the pick of the puzzles from the recent UKPA Sudoku Championship. Many congratulations must go to our first champion Warren Harvey, a long-time reader of this blog. He topped the British contingent with a winning score of 100 points.

There was an incredible international participation too, the size of which took us aback. The top three of the table in a field of genuine world beaters were in third place Hideaki Jo of Japan, who completed the set and scored 240 points. Just a minute quicker to solve all of the puzzles was Yuhei Kusui, also of Japan with 242 points. However the clear winner was Florian Kirch of Germany, top of the pops with 256 points, completing the puzzle set with a most impressive 8 minutes to spare. Many congratulations Florian, if you’re reading, and good luck to all my other German readers who used this as a warm up to the forthcoming German championships.

As to the reasoning behind these pick of the puzzles; it’s simple. The puzzles I made I wanted to be unique amongst the background of their sub-family of Sudoku variants. With these, I succeeded and then some. I haven’t seen any puzzles anything like either of these two. Enjoy!
    #102 Killer Sudoku – rated hard

    #103 Arrow Sudoku – rated hard
All puzzles © Tom Collyer 2009-10

Friday, 5 November 2010

Friday Puzzles #77

Greetings all – just a quick update this week. The first two puzzles are taken directly from the instructions of the imminent UKPA Sudoku Championship. Please note that the second link takes you to a groovy new tournament page.
    #098 Irregular Sudoku – rated easy
 

     #099 Touchy Sudoku – rated medium
Please refer to the puzzle examples section of the instructions linked above to refer to the rules. I can’t really be bothered to copy and paste them here! You’ll also have the novelty of finding the solutions there too!

For my 100th published puzzle, I’ve decided to let myself go a bit. Yup, another twisted symmetry 10×10 masyu – but I reckon this one is probably harder than last week’s offering. Rest assured that I’m going to stick to my guns on this and still call it a medium – just! I am particular pleased that almost by accident I stumbled upon a way of implementing the sort of non-trivial global logic I’ve wanted to put into a puzzle of this size for a long while now. The finishing move is pretty subtle as well, but no less cool for being so. Enjoy!
    #100 Masyu – rated medium
All puzzles © Tom Collyer 2009-10

Monday, 1 November 2010

UK Puzzle Association Sudoku Championship

As promised, here is some information regarding this event that I’ve been tirelessly working at for about 6 months. Honest!

Here’s a forum discussion thread: http://forum.ukpuzzles.org/viewtopic.php?f=5&t=61

And here’s a link to the instruction booklet: http://www.ukpuzzles.org/downloads.php

We don’t quite have the web interface live. The registration process is going to be handled via the forums, so if you wish to compete then you’ll have to sign up. Because this isn’t quite done, if you have already registered, you will probably have to go and change some of your account settings (e.g. your name and your nationality) in the next few days.

That’s about it for now – more coming soon!

Friday, 29 October 2010

Friday Puzzles #76

So after the treat I served up last week, I’m afraid it’s time to come down to earth a bit this time around. This is one of those promised weeks where I’m serving up a puzzle featured in the recent LMI puzzle test I was responsible for. Albeit this one was fairly well received. I suppose that a possible ulterior motive for posting a slitherlink puzzles is that recently I have been in the habit of solving at Kwon-Tom Loop – which is curious as I don’t really enjoy the puzzles there that much. They are all taken from the generator and whilst all are certainly challenging, there is no elegance to them. On the other hand, I think that when you have a hard puzzle there should be a certain je ne sais pas to the solve that feels like getting a good bit of logic is being rewarded. Hopefully you get this here.
    #096 Slitherlink – rated hard
Ah what the hell, why not have something original? I’ve been on something of a roll with my twisted symmetry masyu recently (it’s very therapeutic to design them) – and whilst it’s fair to say that most of them are fairly trivial to solve and I should really try making them in sizes larger than 10×10 – I am a bit pleased with this one as it’s by no means a trivial solve. So I don’t think that I could ever call a 10×10 masyu hard, but this at least isn’t totally easy. Enjoy!
    #097 Masyu – rated medium
 All puzzles © Tom Collyer 2009-10

Finally, I’d like to offer a hearty congratulations to all competitors at the 19th World Puzzle Championship in Warsaw, Poland. I wasn’t out there myself, but I have been following the progress of the British contingent via the UKPA forums with great interest. See also Thomas Snyder’s blog (over there on the left – I’m getting tired of linking everything).

Special congratulations should go to the nikoli.com solving behemoth, Hideaki Jo, of Japan, who finished third; to seven-times world champion Ulrich Voigt of Germany; and finally to the new world championship himself, Taro Arimatsu, also of Japan. You might surmise that the Japanese had an excellent time of it out in Poland, but they were ultimately pipped to the post by an excellent American team. Not only did they feature Mr. Snyder on the left there, but for the first time none other than Palmer Mebane – a.k.a. MellowMelon – whose blog you can also find there over on the right. So I suppose the final congratulations go to them.

Really finally, expect news of the immanent UKPA sudoku championship very soon!

Friday, 22 October 2010

Friday Puzzles #75

A.K.A. Tom Collyer finishes unfinished business

A.K.A. Tom Collyer keeps his promises (at least sometimes, at any rate haha…)

A.K.A. Who needs a list of pentominos by the side of a puzzle anyway?

So this is a tough cookie. But it’s worth it, I promise you. 75% solves beautifully well, and the last quarter is a bit of a head scratch. If it’s too much of a head scratch, you can probably trust my good nature and use a few hinted shortcuts to finish the puzzle. Enjoy!
    #092 Nurikabe – rated hard
P.S. A few weeks back I eulogised about how great my Marathon puzzles for the LMI test were. As it turned out, the test was somewhat of a disaster, with a high proportion of broken puzzles and plenty of egg on my face. That said, there were still some rather good puzzles and you can probably expect to see a couple of them reposted on my blog on weeks when I’ve not got a spare mo to do a semi-decent puzzle.

Anyhow, the Heyawake was actually broken – which made me die more than a little inside because if you skipped over the contradiction the mistake implied, it was in my opinion the best of the three puzzles. I did fix it, but it’s not the same :(.
    #093 Kakuro – rated hard

    #094 Masyu – rated hard

    #095 Heyawake – rated hard
All puzzles © Tom Collyer 2009-10

Friday, 15 October 2010

Friday Puzzles #74

KISS

As much as I’d like to go on about a rocking American band of the 70’s, I think I’d better Keep It Simple, Stupid. Especially in light of recent puzzle-writing dickhead errors on my part. So what could be more simple than a 10×10 Akari?

Well: I haven’t posted the rules before (competent use of the mouse in a leftward direction should help you here); and 10×10 Akari are usually lame. This one isn’t. Enjoy!
    #091 Akari – rated medium
All puzzles © Tom Collyer 2009-10

Friday, 8 October 2010

Friday Puzzles #73

I write today at silly o’ clock in the morning as something of a broken man, in terms of writing puzzles anyway. For today’s post, I would have loved nothing more than to share the three “marathon” puzzles I have written for the LMI October Puzzle test, my so-called Nikoli selection. In my judgement, they are 3 of the best puzzles I’ve done so far, and as a threesome they encompass some great design, some excellent solving manoeuvres which will be familiar to long-time readers of this blog, some more that will be novel; sometimes with a highly slick solving feel, other times with some fairly challenging logic, and yet more times where you suddenly notice something really neat that you really weren’t expecting.

However, I can’t very well go and publish them early now, can I?

Instead, I have fallen back on my trusty friend, the 10×10 Masyu, with (almost) twisted symmetry. This is one I made waiting for the rounds to finish at the Times sudoku championship last month – and I was thinking about including this for LMI until I made an even prettier design. So yeah, lazy this week. If it’s any consolation I believe there are very few people – if indeed there are any at all – who do these better than me. Enjoy!
    #090 Masyu – rated easy
All puzzles © Tom Collyer 2009-10

Friday, 1 October 2010

Friday Puzzles #72

This week I am publishing puzzles as a sort of bridge burning ceremony. These were initially scheduled to be part of the forthcoming UKPA Sudoku Championship but have had to be left out for editorial reasons. This is obviously as painful as choosing which of your favourite offspring to save from the meat grinder, but now they are out there’s no going back.

Perhaps the best way of thinking about things is this: if these were the puzzles that got the chop, how good are the ones that survived going to be?

Enjoy!
    #088 Consecutive Sudoku – rated easy/10 points
(Digits in adjacent cells may be consecutive if and only if a bar between the cells is present)
    #089 Deficit Sudoku – rated easy/10 points
(Place the digits 1-9 exactly once in every row and column, and at most once in the 10 marked 8-cell regions.)

All puzzles © Tom Collyer 2009-10

P.S. Earlier versions of the consecutive had a bar missing, this one does not!

Friday, 24 September 2010

Friday Puzzles #71

Today I must start with a bit of a confession. Whilst it might surprise those readers with longer memories, I do try and put out puzzles on a Friday that solve uniquely. However, I’m not entirely sure I want to do the same this week.

Let me put it like this: Numberlink.

Numberlink in my eyes has something of a notoriety as a puzzle because whilst the rules are deceptively simple, you are actively encouraged to use metalogic – things like assuming all the squares are used, and that the solution is unique – to solve it. You can read more about it in MellowMelon’s excellent post here:

http://mellowmelon.wordpress.com/2010/07/24/numberlink-primer/

Of course, this provides the author of a Numberlink puzzle with a headache – after all, you can’t use the same solving meta-logic or you might end up with something like this:


Which most certainly does not solve uniquely. What I did was start off with a blank grid, and then filled it up with strands. As it turns out, the way I packed these strands together wasn’t “tight” enough, and there is plenty of the sort of wriggle-room you need for multiple solutions. Actually, I should confess before you go hunting for what I originally had in mind, that this was rather naughtily designed to leave exactly one square blocked off and hence left blank. This has nothing to do with the uniqueness of the solution however; you can rather trivially push one of the clues up by one square to get one particular solution that fills up the grid.

Nevertheless, I am convinced there is some logic dictating the uniqueness of a Numberlink solution. My proposed statement goes something like:
Suppose we are given a Numberlink puzzle (a grid with pairs of clues needed to be joined up), and a solution to the Numberlink puzzle that uses up all the squares. Then if this solution has “The Right Properties” then it must be unique.
Quite what The Right Properties are, I’m not entirely sure. One particular strategy is showing that the set of all solutions to a Numberlink puzzle are basically fiddles of each other, each related by a series of something akin to the Reidemeister moves of knot theory. Once you know what all the fiddles are, checking uniqueness of a solution comes down to scanning your candidate solution and seeing if you can apply any of these fiddles – using what I vaguely described as wriggling-room – to get a new solution from it.

One particular example was supplied by Andrey Bogdanov via the UKPA forums – a truly excellent resource – which means that the statement has to say something about symmetry, and what Topologists might call hyperelliptic involutions!

Anyhow, that’s nothing anything close to being rigorous, but I believe there’s a useful strategy there for those that are interested to take a look at. I’m sort of hoping that there might be multiple solutions to this one. Finding another solution to what I have in mind as “the” solution didn’t happen in the 5 minutes I had a quick scan over – so if there is indeed another solution I’d be interested in seeing what it looks like!
    #087 Numberlink – rated medium. Maybe.
All puzzles © Tom Collyer 2009-10

P.S. I know I definitely get some Japanese traffic to this blog, so if you are in the know – there are after all humongous nikoli Numberinks which would surely be impractical for a computer to check uniqueness – then please speak up :)

Monday, 20 September 2010

Poor Tom

If you don’t want to read on, then this picture sums up my fortunes rather neatly:
Circled is a closed subset of wrongly permuted digits that ruled me out of the grand final of the 2010 Times National Sudoku Championship. Instead, the deserving winner of the Championship was George Danker, who correctly solved the four puzzles of the grand final in the fastest time. In second place was two-time champion Nina pell, and in third was Mark Goodliffe – the current Times Crossword Champion.

The Longer version starts here.

I popped on a train down from Coventry to Euston on the morning of the championship, joined by Andy at Milton Keynes. After stopping off at the M&S food place at Euston to buy some lunch and a water bottle, we made our way to the Institute of Education – handily located about 5 minutes away. Once inside, it was excellent to catch up with a few familiar faces – first up was fellow WSCer George Danker together with his supporting entourage of his parents and girlfriend Sophie. We were joined by Mike Colloby, and crossworders Simon Anthony and Mark Goodliffe (see their website http://www.piemag.com/ if you like that sort of thing). I always feel a bit sorry for the other people before the event, because they generally are sat down looking very nervous, perhaps solving a puzzle or two, but mostly all in awkward silence. I hope they comforted themselves with the goody bag, which also included a card advertising the forthcoming UKPA Sudoku Championship as well as a newspaper. As ever, the bit with the sudoku was curiously absent.

Anyhow, onto the first preliminary. The format, same as ever was one hour to do four puzzles. I made sure to get a desk at the front, for minimum of distraction, and couldn’t well resist taking the desk numbered 81.

I started this round well, cleanly getting out the first puzzle. I hit a bit of a sticking point with the second, so decided to move on. This wobble started to pronounce itself as I messed up the third puzzle fairly early on into the puzzle – no matter, deep breath, bit of rubbing out, out it comes cleanly. Phew. Puzzle four was the best yet, whizzing through with no hitches, leaving me just to get on with the second. I couldn’t see anything in the notation I’d already put down, so after maybe a minute I decided to take a punt and guess. This seemed to working beautifully, until I realised at the end that there was an apparent uniqueness issue. Alarm bells start blazing in my head, and the only option was to go nuclear with the rubber. This had the relieving effect of showing an obvious resolution of the 28 pair in the third row. Rest of the puzzle comes out cleanly, and I declare in 8th place in a time of around 24 minutes, having performed my checking routine of checking for unfilled squares. I was unsure about the time, but this is what George reckoned having declared a few seconds earlier.

This was pretty slow by my own standards, but I was only really warming up, and the lost time was easily explained away by my wobbles. My solving speed was good, and this was the main thing. In the break I was glad to have a chat with Simon who said that I wasn’t the only one to have had a hiccough – he reckoned he had solved six and a half puzzles in the first part. For the rest of the break I settle down on the floor with Andy and read a bit of the paper

The second part of the preliminary was much the same, four puzzles to do and an hour to do them in. This time I was ready to regain a bit of face, and this was the case as I caned up the first puzzle, being fairly sure that mine was the first fiddling about with the paper to move onto the second puzzle in the room. Again with the second puzzle I start well, but then hit a hitch. No matter, move onto the third. A similar story, and was about to go onto the fourth until a spot something fairly clever with either pairs or triples, and the puzzle then fell pretty quickly. On to the fourth – I get through this quite quickly, but see a conflict with a 5 right at the end. Balls! I start rubbing out, started again – then saw where the error lied in my first attempt! Easily corrected and so with the imprints of my first go still there I hastily put the numbers back in. It seemed to solve fine. OK, back to the second – again I saw what I was missing and quickly blitz through this too. A quick check for empty squares reveal a couple in the first puzzle – fill them out, and again I declare.

I initially reckoned this must have been in 15-20 minutes, but Mark Goodliffe reckons that was more the timespan he got the second set done in; I had finished a long way ahead of anyone else in the room, making my time closer to 10 minutes. Which if true would be a time competitive with any Sudoku solver in the world. At any rate, it left me with a lot of time sat at my desk. As with the first preliminary, I spent this making 10×10 puzzles in the notebook that came in the goody-bag. Cumulatively, I now have a good collection of Masyu and Nurikabe to publish here at a later date!

Back to the narrative. The end of the second preliminary drew close and David Levy was ready to announce the 8 grand finalists. Having only been 8th in the first part of the preliminary, I was expecting to hear my name fairly early on. I was pleased to hear the names of Mark Goodliffe in 6th place, and George Danker in 5th. When I heard that there was a three-way tie for 2nd place, I thought this had to me. First name was read out. Shoot. Second, again not me. Third – Nina Pell.

Shit shit shit. Shiiiiit. I couldn’t possibly have been first could I?

No. That went to Stephen Gerrard.

Not again! Not again not again!

In retrospect, it is plain to me that the error must have been on that fourth puzzle, which I hastily redrew the numbers in for. I must have copied over one bad egg or something. I should have checked it more thoroughly. Caning up the entire room by a clear 5 minutes, and I hadn’t checked carefully. What an absolute idiot!

After the finalists were congratulated, David Levy mentioned that if anyone who expected to place higher (me) then they should come over and the error of their ways was to be pointed out. I duly did so, at this point convinced I had screwed myself over, and asked “I’m sure that I did make a mistake, however I’m curious as to where it was”. What I saw was the picture above, indeed from the fourth puzzle.

ERRRRRRRRRRRRRRRRRRRGGGGGGGGGGGGGGGHHHHHHHHH.

In retrospect, I think there are two parts to the reasoning as to why I hadn’t checked my second preliminary set more closely. The first is that when solving on paper, I normally catch my errors when solving, and restart. The most likely thing I will do to mess up is simply leave cells blank. I have learned this from previous years, and now make sure to do an empty cell check in all competitions. In short, I felt I had done enough checking. The second part to the reason is far uglier. On the way to winning last year, I had placed 7th in both parts of the preliminaries; solidly and unspectacularly. Having been 8th in the first part this year, I wanted to make my mark. Simon had mentioned that with regards to my nikoli times, I was certainly getting faster. In short then, I hadn’t wanted to the statement I was making to the room to be watered down by spending too much time checking.

Whilst the second half of this reasoning probably smacks of hubris, I think it is only fair to mention that the first half of the reasoning is crucial to this too. With my current procedure, I reckon I catch 80-90% of my potential dickhead errors.

After having finished with the judging team, I had a quick word with the photographer, who seemed familiar from last year but as it turned out wasn’t, and mine was a common enough mistake! Apparently she had taken enough photos of me to warrant taking my details, and overall seemed a good sport. I also shared some kind words with regular reader David Collison, which was very nice!

I decided to stick around for the grand final – firstly because my good friends George and Mark were involved, and secondly because I wanted to start the cathartic process by solving alongside them. I wished George all the best, hoping that he’d win to maintain the integrity of the UK WSC team from April. Mark mentioned that as always, he didn’t think he had the raw speed of the likes of George or Nina, but was going to maximise his chances via a bifurcation strategy – much as he had done in 2007 when he reached the final. I think the common consensus at this stage was that Nina was probably the favourite. At this point I was engrossed enough with what was to come that my own failings didn’t seem to matter too much. After all, I’ve one this twice before – and mistakes happen to the best of us!

So, on to the final. Firstly I’ll state that the puzzles were pretty tough – a little harder than what are published as super-fiendish these days. Whilst I was a little slow in places, I generally had no problems with the puzzles (I have always thought that generally my advantages as a sudoku solver are exaggerated by harder puzzles), working through them fairly rhythmically although a little stickily in patches, getting them out in 21 minutes, as timed by Simon who had also stuck around for the final. I reckon this was a little over par by my standards, although I think I’ll post them up later if people are interested to see how their times stand up.

The action with the grand finalists was intriguing, with the apparent difficulty of the puzzles being reflected in the faces of the competitors, together with the regular sound of someone rubbing out and presumably start a puzzle over. Mark was the first to declare – something of a shock – but apparently his bifurcation strategy had paid off handsomely. A little while – perhaps four or five minutes later – after him, George then finished, looking a little resigned. Again there was a gap of a few minutes, before Nina finished. I sort of switched off a bit here – focussing on finishing off the slitherlink puzzle I was writing.

The twist was to come after the time was up. Of the eight papers, David Levy announced, only two had all of the four grids completed correctly. Not what you wanted to hear at all! Moreover, it took what seemed like an absolute age before the results were clear, and the final standings announced. The big gasp came as Mark was announced as third place – indicating that the final two placings were Nina in second, and George as champion.

I tried to make eye contact and give him a big thumbs up. With all respect to Mark and Nina, I am glad that George did win. Having solved side by side with him in Philadelphia at the Worlds last April, I can safely say he is a top notch solver with a bright puzzling future ahead of him. This kiss of death now perhaps, but if he decides to compete I think he’s the clear favourite for the UKPA championship too. Most definitely a worthy champion!

It was also announced that the third puzzle of the set was the hardest – this seemed to be confirmed by the experiences on the sidelines; both Andy and Simon had gotten stuck at exactly the same point. Rather frustratingly, I couldn’t see where to point out the next step in the puzzle, despite having made pretty easy work of it minutes earlier. After about 10 minutes, I finally saw the blaringly obvious – a 179 triple in the 6th column.

We stayed for the presentation – interestingly enough the junior (best finish for 15 and under) was awarded the same prize as everyone else – a Time atlas of the world to which I could only think what does a 15 year old want to do with that? After exchanging a few last pleasantries with Simon, Mark and Nina, that was that – I headed off. One last regret was apparently missing Times journalist and most excellent drinking buddy Jack Malvern for all the journalisty bits. I shall have to keep waiting for the appearance of the phrase “brain fart” in Britain’s most reputable newspaper.

There’s always next year – my record so far is: 06 beaten by David McNeill; 07 won; 08 defeated by myself with a massive brain fart; 09 won; 10 again defeated myself with a dickhead error; so hopefully things look good for 2011! Thanks for reading!

Friday, 17 September 2010

Friday Puzzles #70

So this week time has somewhat ambushed me and I don’t really have anything brilliant to share. Given that I’m going to be busy at The Times national sudoku championship over the weekend, I can’t really cop out and offer to post something up later either. Do expect another hideously long and boring report coming soon. Haha…

So what I’m left with is basically the beginnings of an idea that will hopefully get off the ground after the official UK Puzzle Association’s 1st Sudoku Championship. No harm in a shameless plug, even though there a few things left to be sorted out there. Anyhow, back to the idea. What we have is a Standard Sudoku, only I’m telling you that exactly three (3) of the given clues are wrong. You can probably tell this is very much an initial concept puzzle, but it’s the best I’ve got this week – sorry!

Also (with a seamless change away from personal failings), last week I also forgot to plug the latest issue of Dr. Gareth Moore’s Sudoku Xtra. The latest issue (#10) features a wide selection of good puzzles from Gareth + more – including a Sudoku Islands puzzle from yours truly. Definitely recommended!
    #086 Wrong Sudoku – rated easy
All puzzles © Tom Collyer 2009-10

Friday, 10 September 2010

Friday Puzzles #69

So this week I’ve decided to keep playing with the alternative presentation of Yajilin. My argument at this stage is that this really isn’t a stand-alone Yajilin variant, and to reply rather lately to the comment MellowMelon made on the last post that yes, I agree that in general it isn’t too hard in filling up the grid with “useless” clues. With this presentation, I could indeed have gone through that process this week, but there are two main reasons why I’m serving you up the following.

Firstly I couldn’t be bothered. What can I say, maybe I’m lazy, maybe I just need the right motivation. But secondly, I think the shaded squares add a certain something to the aesthetic appeal of the puzzle over, let’s face it, is otherwise a rather barren looking grid.

Certainly, this is a different sort of solving experience going on here, working out the claustrophobic implications of the narrow passage ways than you’d see in your average Yajilin puzzle, but I think it must be reiterated that it’s an easy job to put these back into “standard” presentation.

But you’re probably getting bored reading all that, and would much prefer some puzzles to solve. Enjoy!
    #084 Yajilin – rated medium
[My apologies for inconsistent and unsolvable early versions of #084. For the record, the top left clue went from being unmarked, to being a 0, and finally to its correct status as a 2:)]
    #085 Yajilin – rated medium
All puzzles © Tom Collyer 2009-10

Friday, 3 September 2010

Friday Puzzles #68

For this week’s puzzle, I’ve decided to have a little play with Yajilin, and its presentation.

A problem I quickly ran into was with how the clues have an effect on the puzzle. It wasn’t too long into making this that I had a nice symmetric pattern laid out in the grid, and a few clues in place. As I continued putting in more and more clues, it became increasingly obvious that I wasn’t going to need all the marked squares for clues that I’d set aside. However, I also realised that I couldn’t simply throw them away (for one thing, think of the symmetry!). But more importantly, because the rules of Yajilin say that you have to use every square in the grid, these as yet clueless squares were still playing a crucial role in the solving process.

As such I’m going to throw you two versions of the same puzzle, presented slightly differently. For the first, I filled in the the clue squares I needed, sometimes ridiculously, and sometimes a little more obscurely, all the time trying not to introduce too many logical short-cuts into the puzzle.

I am not sure then, that despite having more information in the first version, whether actually the second is a nicer solve. 
    #083a Yajilin – rated hard
Note in this version that you can shade in a square directly adjacent to a blank grey square, although the loop definitely cannot enter these squares. Also note that the the grey squares aren’t included in the count of the to-be-shaded squares.

I’m hoping I’ve deleted the right clues, although I suppose it’s not the end of the world If I’ve gone too far. I think it should work out that there are probably still one or two technically surplus clues hiding in there.
    #083b Yajilin – rated hard
All puzzles © Tom Collyer 2009-10

Thank You

Nope, not this week’s puzzle just yet, it’s still Thursday (just)!

Anyhow, no doubt exasperated with my makeshift attempts to post up the last two Friday Puzzles – which I might add for my own moral satisfaction were drawn up and on the camera on time – David Millar of The Griddle took matters into his own hands and drew them up, undoubtedly to make the solving experience a little easier than working from those photos!

Anyhow, he has very kindly shared these with me, and saved me the bother of drawing them up myself!

Thanks again David!

Thursday, 2 September 2010

Thursday, 19 August 2010

When The Levee Breaks

OK – well not the levee, but my laptop. It’s currently in for repairs together with all my bits and bobs for publishing puzzles. So tomorrow’s puzzle will be delayed for “a few working days”. My other option is to whip something up in my pad, and take a photo of it, and perhaps find a computer in the maths department with an SD card slot or something. Sigh – maybe not.

This is trebley bad timing, what with a nikoli.com sudoku time trial tomorrow, and the USPC on Saturday. Hopefully I can find a good place to compete in both of these without affecting my performance too much!

Friday, 13 August 2010

Friday Puzzles #65

Welcome once more to another edition of Friday Puzzles! To those who are just (de)tuning in, I’d like to introduce you to my own pet sudoku variant, Sudoku Islands. The idea is the result of blending Sudoku and Nurikabe together. I’ve realised that since introducing them earlier on in the summer I’ve not really given a proper description of the rules. So here goes:
Place the digits 1-N in the grid such that each digit appears exactly once in each row, column and marked S×T box. The cells containing digits form a connected region of the grid, not containing any 2×2 block of cells. The remaining cells are shaded islands, whose sizes are given. Each island is clued in the grid.
Previously, N has equalled 5, and S and T have both been 3. Here’s a little recap in case you were wondering how that looks practically.
    #079 Sudoku Islands – rated medium
This example ramps up N to 7, and S and T have become 4 and 3. 12×12 classic Sudoku puzzles are something of a drag; I’ve intentionally made this one fairly difficult, although I’m not quite sure whether this size again makes things a little bit fiddly. Let me know what you think!
    #080 Sudoku Islands – rated hard
All puzzles © Tom Collyer 2009-10

Friday, 6 August 2010

Friday Puzzles #64

This week’s puzzle is partly inspired by something that my good friend Jason Z (Ziti) sent to me earlier this week. It is probably also the most difficult puzzle I’ve ever made – If I used more than three ratings to classify my creations, then there’d have to be at least one or two more above “hard” to accommodate this beast. As it is, this is only “hard”. Enjoy, and give yourself a pat on the back when you’re done!

Edit: It appears the Warwick servers are playing up, so this may add to the challenge of solving the puzzle; I’m afraid there’s nothing I can do about that. On the other hand, it gives me a chance to plug Sudoku Xtra – whose 9th issue is now out. Contrary to the name, this magazine features a lot of puzzles which are decidedly not sudoku, and is well worth a look. This month’s edition includes the recent (not this week’s that is) Heyawake and A/S Heyawake puzzles that have featured on this blog, as well as contributions from David Millar (who has put together a sudoku competition this weekend) and puzzling friends mathgrant and MellowMelon.
    #078 Heyawake – rated hard
All puzzles © Tom Collyer 2009-10

Friday, 30 July 2010

Friday Puzzles #63

There was a neat little trick I put in last week’s generally well received nurikabe puzzle that I’ve decided to play with a bit this week too. I haven’t really had time to turn this one up to 11, but this at least remains a difficulty level above from your standard 10×10 size puzzle.

Edit: This version slightly modified from what appeared on Friday
    #077 Nurikabe – rated medium
All puzzles © Tom Collyer 2009-10

Friday, 23 July 2010

Friday Puzzles #62

It’s been a while since I’ve done a nurikabe puzzle, although I seem to recall that I always seem to have a bit of a moan about how my nurikabe aren’t quite up to the highest standards. This, as opposed to something like my Masyu puzzles which I believe are as good as anything bar juno. It’s a similar story here – this puzzle has quite a nice “solving flow” to it, but it’s not quite as polished as I think it could be – which is not to say I didn’t give it my best shot! Nevertheless, I think this is a pretty nice idea, and will certainly have you scratching your head for at least a moment.

Interestingly, I’ve seen my traffic drop off a little bit in the last couple of weeks, which coincides with the end of the Warwick term. I’ll be keeping going throughout this summer period, but for now, enjoy!
    #076 Nurikabe – rated hard
All puzzles © Tom Collyer 2009-10

Friday, 16 July 2010

Friday Puzzles #61

Another puzzle week busy making sudoku, and now also this slitherlink puzzle. Nothing too taxing, but hopefully enjoyable enough. Tested properly this time, too! 
    #075 Slitherlink – rated easy
All puzzles © Tom Collyer 2009-10

Thursday, 15 July 2010

We're Gonna Groove

‘Fraid it’s not an early Friday puzzles entry, instead I have a couple of puzzle related announcements to make to all you friends, Romans and puzzle fans.

First up. The UK Puzzle Association is proud to announce its new (albeit still under construction) website, http://www.ukpuzzles.org. The UKPA will be the representative body for the UK to the World Puzzle Federation. What this means in practice is exciting new times for all British based puzzlers, with lots of projects in the pipeline. There’s already a discussion forum, with top notch puzzles, as well as probably the best Sudoku competition this side of a WSC to come. Although I might be slightly biased on that last point!

Secondly, a little pointer towards another promising looking Sudoku competition at the weekend, hosted by LMI and written by two-time World Champion Jan Mrozowski. Read all about it here and the competition page is here.

Finally, my partner in PhD-ing crime, Mr. Robert Tang has in his spare time been helping to organise the annual Sydney University Mathematics Society Puzzle hunt. This sort of thing is no doubt inspired by the (probably) world famous MIT Mystery Hunt, so if that’s the sort of thing to float your boat then you should mosey on straight down here

That is all. I’d better go write me a Friday puzzle!

Friday, 9 July 2010

Friday Puzzles #60

Busy. Easy masyu. Small is beautiful. Mistake. Fix. Not quite so beautiful. Meh.
    #073 Masyu – rated easy
One that works first time. Enjoy!
    #074 Masyu – rated easy

All puzzles © Tom Collyer 2009-10

Friday, 2 July 2010

Friday Puzzles #59

So a week or two back I saw a wonderful twist on the rules of heyawake, courtesy of Grant Fikes. I’m sure the more adventurous browsers of this blog will have already come across his wonderful page, but for those who haven’t then give it a visit.

Anyhow, the twist is this: instead of numbers in the rooms indicating which squares should be shaded in, rooms are labelled with either S, A, or not at all. Rooms labelled S should have squares shaded in with 180 degree rotational symmetry (which includes no shading at all), whereas rooms labelled A definitely cannot have that 180 degree rotational symmetry. Rooms with no label can be shaded any which way you like, provided you don’t break the other heyawake rules, which if you’ve forgotten can be found on the very handy “how to play” section there on the right. Anyhow, Grant’s puzzle was fairly gentle, but here I’ve been a bit keener to explore some of the logic, and how it interplays with some standard heyawake tricks.
    #070 A/S Heyawake – rated hard
I should also mention that some puzzles from a while back have been featured in the 8th edition of Dr. Gareth Moore’s Sudoku Xtra magazine. This is quite a cool magazine, and whilst I should stress that I’m receiving no commission or anything, it is definitely worth a look for all you puzzle fans – it’s packed with a lot of nice puzzles. As well as those WSC5 style puzzles I did, it features the Sudoku Islands puzzle from last Friday. So what the heck…here are a couple more. These are definitely on the easy side of things, but I do have some trickier ones in reserve that are part of my ongoing sudoku project. Enjoy!
    #071 Sudoku Islands – rated easy
    #072 Sudoku Islands – rated easy
All puzzles © Tom Collyer 2009-10

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