All 11 entries tagged Sudoku Variants

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June 04, 2010

Friday Puzzles #55

Mission accomplished! Weekly numbering is now completely in order. Modulo the missing #7 and #17 that is. Still, there were a couple of weeks where I made bonus puzzles so I think that just about balances out the equation. I must add that I revisited the double-toroidal sudoku, but I have to say that with its current grid I lost a bit of interest.

Anyhow, a sudoku variant this week which I think I’m right in claiming has only ever been pulled off by yours truly – although please correct me if I’m wrong. In case you missed the original post the idea with 10’s sudoku is normal sudoku rules, except that every time a pair of adjacent cells had digits summing to 10, they are marked. Where there are no markings between adjacent cells, the conclusion is then that the relevant digits cannot sum to 10.

Prior to that post, I can’t find an example where 10’s sudoku had no such marked occurrences between pairs of digits, but it turns out with a bit of work that it’s perfectly possible. I’m sure a computer-y type would easily be able to write a program to churn out more of these without working up any sort of a sweat, but that’s not the way I roll. There’s plenty of potential with this variant to churn out some really fiendish challenges; this example is fairly plain sailing, but perhaps with a couple of surprises along the way. Enjoy!

UPDATE: My apologies to those who had a go at an earlier version of this puzzle, which had two solutions, and my thanks to Jack who pointed this apparently obvious blooper I managed to completely miss! My reputation for errors seems to be growing, but stick with me anyway – at the very least you won’t be bored!

#065 No Tens Sudoku – rated medium

All puzzles © Tom Collyer 2009-10

April 25, 2010

Friday Puzzles #42

Yes not a Friday. I don’t care! This is fortress sudoku. Notice the shaded “fortress”. The numbers that go in these shaded cells must be bigger numbers than those in unshaded cells immediately adjacent to them. Enjoy!

#052 Fortress Sudoku – rated medium

All puzzles © Tom Collyer 2009-10

April 23, 2010

Friday Puzzles #41

So sudoku fans, with less than a week to go until the world sudoku championships, I’ve decided to spoil you rotten.

Here are three puzzles that will 100% definitely appear in the championships in a form quite similar to what I’m giving you. Additionally, I’m going to try and publish a puzzle a day until next Wednesday, each one a variant definitely appearing in Philly.

This week, I give you: Integer Division Sudoku, Surplus Sudoku and Deficit Sudoku.


#049 Integer Division Sudoku – rated easy

#050 Surplus Sudoku – rated easy

#051 Deficit Sudoku – rated easy

All puzzles © Tom Collyer 2009-10

April 16, 2010

Friday Puzzles #40

So my sudoku variation bandwagon keeps on a-rollin’. This week, non-consecutive sudoku. This is basically sudoku as you know and love it, but with the added constraint that no two adjacent cells can contain consecutive cells. As with last week, this is my first attempt at constructing one of these variants, and whilst decent enough for me to put my name to it on this blog, it doesn’t quite (in my opinion) reach the standards of a perfectionist. Enjoy!

#048 Non-consecutive Sudoku – rated medium

All puzzles © Tom Collyer 2009-10

April 09, 2010

Friday puzzles #39

Another sudoku variant this week, this time “extra region”. This does what it says on the tin really, same sudoku rules with the added constraint of having 1-9 in the shaded regions as well. This hasn’t really come out as perfectly as I’d have liked in terms of the logic needed to solve this, but I suppose the consolation is that it’s not too difficult. Enjoy!

#047 Extra Region Sudoku – rated medium

All puzzles © Tom Collyer 2009-10

April 03, 2010

Friday Puzzles #38

A belated entry this week, as I have been travelling somewhat. There’s more travelling to look forward to at the end of the month too, with the world sudoku championships in Phiadelphia. As such, this week’s puzzle is a sudoku variant known as Arrow Sudoku. Standard sudoku rules apply, and additionally, the number that goes into a grey circle is precisely the sum of the numbers to be found on the corresponding arrow.

Do note that numbers can repeat on the arrows, and enjoy!

#046 Arrow Sudoku – rated hard

All puzzles © Tom Collyer 2009-10

February 19, 2010

Friday Puzzles #32

Welcome to Friday Puzzles, where I am pleased to announce the Puzzled Medium TM 2010 Sudoku qualifiers!!!

The prize you, dearest reader, could win is a once-in-a-lifetime chance to lick your very own elbow, under world championship conditions, whilst looking at this lovely picture of some Philadelphia cheese!

Well, let me temporarily avert your excitement, whilst I lay out the law of the Puzzled Medium TM 2010 Sudoku qualifier. It’s very important you pay full attention to the rules. These can never be broken. NEVER!

First off, this is only the first round. The top 50 entrants will be invited to part two. If I can be bothered to write a part two. Which I probably can, it’ll be good practice for the UK 2010 WSC qualifier, as kindly run by Puzzler Media. By the way, that is in no way affiliated or endorsed by anyone involved with Puzzled Medium TM.

Next is that although the aim of this competition is to find the best and most deserving people to lick their own elbows, do note that one place is already reserved for one of my cronies – who in all fairness has impeccable sudoku pedigree, but never mind the principle of competition or anything. Just bear in mind I do have another crony, who has pretty good (though admittedly not impeccable) sudoku pedigree, including another notable victory in a national sudoku championship (whose puzzles, by the way, were supplied by us at Puzzled Medium TM) and excellent performances when licking their own elbow in the past. He They will definitely not be getting special treatment. We have principles regarding competition!

The eagle-eyed amongst you might have caught on to the fact that being a good sudoku solver has nothing to do with successfully licking your own elbow. This is where you’d be wrong (even though I said fact!) Here at Puzzled Medium TM, we know best, and have a proven track record in previous years of selecting the best people to lick their own arses elbows. Honest.

Oh, please don’t cheat. Here at Puzzled Medium TM, we have never ever ever had any problems with cheating, and it’d be a shame for it to start now. Even though are lots of easy ways to hypothetically do so – for example by using the solvers at Scanraid and then submitting a plausibly competitive time. I shouldn’t really tell you that, but there we are, I’ve crossed it out. You were probably far too stupid to work that out for yourselves anyway.

And before I forget, let me tell you how to submit your answers. After completing the puzzles in an innocent fashion, select 18 digits from each puzzle and send them to me, along with your time. Hopefully your time-keeping device works in a similar sort of way to the ones we keep at Puzzled Medium TM…

Actually, you’ve already seen puzzles 1-4 in this first round of qualifiers in the last three weeks:

Puzzle 1: #036 Sudoku
Puzzle 2: #037 Sudoku
Puzzle 3: #034 Diagonal Sudoku
Puzzle 4: #035 Diagonal Sudoku

Puzzle 5: That’s this week’s novelty – enjoy!

#038 Killer Sudoku – rated hard

All puzzles © Tom Collyer 2009-10

February 05, 2010

Friday Puzzles #30

Oh no I didn’t! You’d better solve this one in a hurry lest anyone look over your shoulder and think you’re some kind of communist scumbag!

Two versions of the “same” diagonal puzzle this week. One is fairly challenging (emphasis on fair there), the other is very challenging, and probably unfair (at least for the purposes of competition). If you’re the sort of person who naively challenges themselves to try the hardest things possible, even when advised not to, then let me say to you the words “Y” and “wing”.


#035 Diagonal Sudoku – rated hard
[censored due to provocative nature of the design of the puzzle]

#035a Diagonal Sudoku – rated (too) hard
[links directly to the puzzle, which is the “same” but harder.]

All puzzles © Tom Collyer 2009-10

January 29, 2010

Friday Puzzles #29

Ok, so here’s part one of my mini-crusade to provide a more enjoyable alternative to those who can’t have a go at the UK WSC qualifiers. And indeed to those who have done or will do them. Puzzler have bastardised the name of diagonal sudoku, and instead call it “X-Factor”. In my opinion this sounds really quite stupid, but there we go, I’m not a marketeer.

This is the first time I’ve written a sudoku puzzle introducing the diagonal constraint. I think It turned out quite nicely, and should make a good warm-up for the coming harder diagonal puzzle.

Incidentally, the remaining puzzles for this initial section will be a harder diagonal, two classic sudoku puzzles, and a killer. Bearing in mind I think the Puzzler killer generator is actually quite good, I’m going to have my work cut out with that, but those are worries for another time. For now, enjoy!

#034 Diagonal Sudoku – rated medium

All puzzles © Tom Collyer 2009-10

August 14, 2009

Friday Puzzles #10

This week comes with a bit of a special theme. The number 10. It’s also very special in that I have managed to get this out and published on a Friday. Wow!

As regular readers may or may not know, last April I participated in the 4th World Sudoku Championships, hosted in a dusty provincial Slovakian town called Zilina. Much was made of the (lack of) quality of many of the puzzles – but one of the most enjoyable puzzles was a variant that appeared in the semi final:

Puzzle M3 – World Sudoku Championship, Zilina 2009

The idea was simple – take a classic sudoku, and mark exactly where an adjacent pair of digits summed to 10. So if a 3 and a 7 were next to each other, a cage was drawn round and marked 10. The twist with this is the contrapositive inference – that is if no cage exists round a pair of adjacent cells, then the numbers inside cannot sum to 10! The puzzle itself had only one such pair of numbers marked – which made me wonder if actually you could go one better and perfect the puzzle.

Well, it turns out you can. After a lot of painstaking work to first even find a valid solution grid, I then wrestled with the task of making a decent puzzle – with my given visual theme. The result isn’t particularly challenging – though not totally trivial.

I do also have a couple of very hard puzzles too. They turned out to be hard almost by chance – they certainly aren’t a particularly pleasant solve in my opinion and so I haven’t bothered publishing them. Anyhow – without further ado, here’s the preamble: place the digits 1-9 in each row column and marked 3×3 box. Digits in adjacent cells may not sum to 10.

#014 No Tens Sudoku – rated easy

All puzzles © Tom Collyer 2009. Well, obviously excepting the world championship puzzle above. I have no idea who to credit that to – and whilst used without permission, I’d like to think that demonstrating it would come under fair use. Anyhow, please respect the rights of the author.


Welcome to the blog of current UKPA sudoku champion, two-time Times national sudoku champion and general logic puzzle fan Tom Collyer.

Home of the original Friday Puzzles, each Friday I publish a 100% original and handmade logic puzzle, inspired by the world-famous Nikoli company.

How to play:
AkariFillominoHashiHeyawakeHitoriKakuroLITSMasyuNumberlinkNurikabeRipple EffectShikakuSlitherlinkSudokuSuraromuYajilin.


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Latest comments

  • I like the appearance of the solution. :P Nice one. by Prasanna Seshadri on this entry
  • I think I've seen something vaguely similar in some of Palmer's puzzles as well. To be honest I've a… by on this entry
  • That's two puzzles in a row where I find something I had used before. I know, not plagiarism; just g… by Bram on this entry
  • Kota, that's not really true. I had made my puzzle before going to the WPC already. Also I don't hav… by Bram on this entry
  • About 20 minutes, after restarting from a mistaken conclusion. by Bryce Herdt on this entry

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