All 21 entries tagged Sudoku Variants

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November 04, 2011

Friday Puzzles #129

So this is my last entry before I jet off to Hungary to have a shot at firstly the World Sudoku Championship, and then the World Puzzle Championship next week. I’ll be travelling with laptop and notebook so there might even be a puzzle next week. I invite you, dearest of readers, to be on the lookout for updates here throughout the week.

For those that are interested, the instruction booklets for each competition are filled with some intriguing ideas.

This week’s puzzle has been taken from the WSC booklet. The only previous examples of these that I’ve seen have been no larger than 7×7 grids, but I’ve whacked this up to full size. The rules are as follows: 1-9 exactly once in each row, column and marked region. Some squares are split in half; exactly one half is to be filled, the other to be left empty. You have to determine which. I’m not totally convinced this is genuinely a hard, but I’ll give it that label anyway what with the novelty value. Enjoy!

#159 Halved Squares Sudoku – rated hard

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All puzzles © Tom Collyer 2009-11

June 10, 2011

Friday Puzzles #108

So in the midst of my triple posting last week, I managed to put out a completely broken Sudoku puzzle, where I’d presumably mistyped one of the digits. Looking back a bit later, I realised it was broken but couldn’t find the dodgy digit, so I went back and changed it.

Anyway, more Sudoku today. This weekend is the UKPA’s Sudoku championship – and I have taken the liberty to put together an example of one of the featured Sudoku variants.

Incidentally, if you want to participate, UK citizen or otherwise, then you should definitely read the instruction booklet and the discussion thread. To actually take part in the test, you will have to be a registered member of the the UKPA forums. Registration is free and easy!

Anyhow, back to the variant. This one has the rather inelegant name of “No Donkey Step Sudoku” – perhaps when I have a free moment (haha) I’ll try and think of something better. Anyhow, the idea is fairly simple. Classic Sudoku rules as you know and love them, with the additional constraint that digits may not repeat within 2 cells on a diagonal line at 45 degrees. If you are familiar with no-touch sudoku, then this is simply a slight extension of the constraint. If you still don’t get it, have a look at my good friend Rishi Puri’s example, which has the advantage of coming with a solution grid. Enjoy!

#136 No Donkey Step Sudoku – rated medium

All puzzles © Tom Collyer 2009-11

June 03, 2011

Friday Puzzles #105

Firstly let me apologise for being absent the previous couple of Fridays. I have been out of the country on both occasions, the logistics being something terrible.

The first Friday was due to being in Beijing on Sudoku duty at the Beijing International Sudoku Tournament. Expect a full report later, but as something of a taster here are the final four puzzles as solved by Jan Mrozowski of Poland and Jakub Ondrousek of the Czech Republic. Jan was the runner up in the event, solving these 4 in a shade over 11 minutes – but Jakub took the crown with a total time of 10 minutes. Needless to say these are both breath taking performances, and whilst everything was broadcast to some Chinese sports channel, I’m not sure the viewers would have kept up – the commentary team of Chen Cen and Wei-Hwa Huang didn’t seem to…

BIST 2011 Final #1 – Sudoku

BIST 2011 Final #2 – Diagonal Sudoku

BIST 2011 Final #3 – Consecutive Sudoku

BIST 2011 Final #4 – Sudoku

[These were reconstructed from photos taken by Bastien Vial-Jaime – hopefully they are all good and typo-free but I haven’t actually had time to solve these myself to verify this is the case.]

With the quality of the puzzles being so high, I’m not sure that I am well advised in starting the first of my three legs of Friday Puzzles today with a sudoku, but there we go, it’s too late now. Enjoy!

#132 Sudoku – rated medium

Edit: Did anyone notice this was broken? I must have typoed a digit when transposing this over to inkscape!

All puzzles – except obviously the BIST puzzles – © Tom Collyer 2009-11

November 13, 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

November 05, 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

October 01, 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?


#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!

September 17, 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/Competition. 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

August 13, 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

July 02, 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 left. 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

June 25, 2010

Friday Puzzles #58

This week dear readers, I am appealing to you for a little feedback. It seems every puzzle designer worth their salt has their own pet sudoku variant they’ve created, nurtured and loved. Oh the long days I looked on in envy!

Anyhow, today that all changes as I’ve come up with something that is (a) original to the best of my knowledge and (b) isn’t totally lame. I call it Sudoku Islands. The idea is basically a hybrid of sudoku and nurikabe. You have an NxN grid, and the idea is to fill in each column, row and box with the digits 1-M, where M < N. Moreover these digits form a connected region of the grid, with no 2×2 blocks, which surround islands. The size of these islands is clued by the grey squares, and there is exactly one given clue per island in the solution. Unfortunately if you are used to nurikabe much, the roles of white and grey (black) squares have become reversed, but you’re playing by my rules now so I guess that’s hard cheese!

What you get is in my mind something that works out to be an improved version of extra space sudoku, where you not only have to fill in the grid, but also have to work out where the extra space is. That’s all beginning to sound a bit wordy, so here’s a really easy toy example for you to get the idea. Fill this grid with digits 1-4 in each row/column/box:

#068 Sudoku Islands – rated very easy


And this one with digits 1-5. Enjoy!

#069 Sudoku Islands – rated medium

All puzzles © Tom Collyer 2009-10


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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