Showing posts with label Sudoku Variants. Show all posts
Showing posts with label Sudoku Variants. Show all posts

Monday, 23 June 2025

Bonus Puzzles from the UKSC

So the 2025 UKSC has been and gone.  Here are a couple of variations of puzzles that appeared on the contest, created by removing some given digits and cages. I checked with solving tools that each had only 1 solution, but to me both seemed too hard to understand fully.  What I can say is that both of these puzzles were set with particular attention paid to the grid geometry - in particular using intersection theory/SET patterns.

On the classic - perhaps there's more to be done with Phistomefel ring?  You didn't need to use this explicitly for the competition puzzle - the break in for that was a series of two hidden pairs.  However, these are now gone with the removal of the given.  I suppose I should also add that the Sudokuwiki solver gets absolutely nowhere with this - in other words this one is off the scale in terms of that measure of difficulty.

On the classic - there's all sorts going on with the larger 2x2 checkerboard combination - but it also seems to me that there's some stuff that limits the permutations within those 2x2s.  The configuration doesn't work with a pure 2x2 grid - you need the L trimino cages in order to disambiguate the solution; that said I think they should be working with the larger checkerboard layout in exactly the same way.  Or not!

It would be interesting to see if any of my dearest readers is able to share any insight.  I would say enjoy, but in this case I'm not 100% sure that experience is guaranteed!
    #363 Sudoku – rated 10/10 [Extra Hard]
    #364 Killer Sudoku – rated 10/10 [Extra Hard]

Friday, 3 December 2021

Puzzle 360: Killer Sudoku

I'm sure this sort of thing must have been tried before, dearest reader.  Not my most elegant work, but the vast majority of the windows will need to be opened if you want to make it through to the end.  Enjoy!
    #360 Killer Sudoku – rated 6/10 [Hard]
All puzzles © Tom Collyer 2009-21.

Sunday, 14 February 2021

Puzzle 356: Arrow Sudoku

Well, I don't see why everyone else should be having fun with arrow sudoku and leave me feeling left out.  Who knows?  Maybe I'll make a few more.  

A.K.A. you need a spare arrow somewhere to break the symmetry.  Enjoy!
    #356 Arrow Sudoku – rated 6/10 [Hard]
All puzzles © Tom Collyer 2009-20.

Friday, 5 February 2021

Puzzle 355: Arrow Sudoku

Look at me - I can make arrow sudoku too! Although perhaps not as difficult as the modern taste demands.  I thought this was fun anyway.  

In case you haven't seen arrow sudoku before, numbers placed in cells with circles must equal the sum of numbers placed along their corresponding arrows.  Numbers placed on arrows may repeat.  Enjoy!
    #355 Arrow Sudoku – rated 4/10 [Medium]
All puzzles © Tom Collyer 2009-21.

Sunday, 27 December 2020

Puzzle 354 X-Sums Sudoku

I had in mind to write a few X-Sums and Killer Sudoku over the next few days, which led me to digging around in my notebook and spotting a puzzle or two that I don't think I'd published anywhere.

Actually I think this one was in the same batch as a similar post I made last year.  I think I originally wrote that batch for someone I care about very deeply and who particularly enjoys X-Sums Sudoku.  Last year’s  post was the better puzzle I think, but I certainly enjoyed myself re-solving this one just now and it certainly seemed too good not to share.

Obviously 2020 hasn't been the best year for many people, but 2019 was also a pretty miserable year for me, and off the back of that I had a period in February this year, before the pandemic set in where I was feeling particularly hurt, betrayed, ignored, unloved, unappreciated and unencouraged.  Maybe that wasn't (and isn't) exactly true, but it certainly felt real enough at the time and was a really overwhelming wave of sadness.  One of the nicer things to happen after that was receiving a message from Simon Anthony, who offered to do a video on one of my puzzles.  Mark, who is a good friend, was very generous with his comments in the ensuing video, which features the puzzle from that same post.  

The whole thing was a kind gesture, as perhaps even back then, pre-pandemic, it was clear that the puzzles that I like to write and the puzzles I enjoy are generally in a very different direction from the puzzles that they like to feature on the channel.  With that in mind I suppose that I'm not surprised that's pretty much the last I heard from them, despite our previous history.  As I've said before, that's not a complaint on my part, it's fair enough, they've moved on and have their own audiences to worry about.  I am certainly appreciative of the gesture when I was at a really low point.  

It was certainly in marked contrast from any support from the WPF, for whom I was half killing myself to write a report trying to provide clarity in trying to classifying sudoku variations.  Looking back, it was a good report and something that I suppose I'm proud of - But equally, it turns out that that was something the WPF didn't take seriously (either in trying to produce it - or then subsequently using when finished), and that the wider community was more or less entirely indifferent to, and so it's hard to conclude that all that effort wasn't entirely in vain.

I felt a similar overwhelming wave of sadness again over the Christmas period - here in London Christmas has more or less been cancelled and I've had to try and cope by myself as best I can.  If I'm being completely honest there have been times where I have not coped at all.  Part of my sadness is that to me, the puzzling community feels as distant now as it ever has - previously it has been somewhere where I could draw a sense of appreciation, strength and support - and I just don't get any of that any more.  I should say that there's no real point or criticism I'm trying to make here, dearest reader, this is just how life goes and sometimes things just move on.  It's more a case of making some observations and trying to process and untangle some knotty threads that have been bringing me down for what is probably a period of over 2 years now.

Better out than in I suppose - I hope my dearest readers have had a happier year than I have.  Enjoy!
    #354 X-Sums Sudoku – rated 6/10 [Hard]
All puzzles © Tom Collyer 2009-20.

Friday, 10 July 2020

Friday Puzzles #303

So by now more or less everyone has heard of Cracking The Cryptic.  Lots of the puzzles featured these days are what I'd describe as curiosities, sometimes with strange mish-mashes of constraints paired together to produce interesting solving gimmicks, sometimes with constraints and solving mechanics that go way beyond anything that resembles classic sudoku.  In any case they represent sudoku variations probably wouldn't retain much in the way of interest once the initial novelty had worn off.  Not that it isn't great to see so many different people I'd never heard of before producing these interesting novelties of course!

One idea that does seem to have a few more legs appeared in a more fiendish form that presented below.  Ahaupt's idea is for you to construct an irregular grid from a regionless start to the puzzle, using clues which give the sums of numbers to be placed in each of the cells the clue sees in both the horizontal and vertical directions up to the border of a marked region, including the cell the clue is contained in.

I think the idea is perfectly nice if you are given the courtesy of the irregular grid to start off with.  You end up with something that is related to Jigsaw Killer, where you combine Irregular Sudoku with Killer Sudoku, but something that I think is a little bit nicer, and with enough differences to warrant calling it a separate Sudoku variation.  I'll call it Signpost Sums Sudoku.

The trade-off with Signpost Sums is that you no longer have the cages represented visually, which is a bit of an inconvenience, but you do have the comfort that you don't have to scan across different regions when looking at the sums, and you get the possibility of having some of the now implied cages to be overlapping.  As each of the sums are entirely contained within one region, it means that you still get to keep the no-repeats condition with the sums.

I've tried a puzzle using a normal 3x3 box layout, and whilst possible I don't think it was all that enjoyable.  Instead I've gone with a couple of irregular grids, one a warm-up, and one towards the harder end of difficulty you might see at a well-balance competition.  I'm kind of hoping I've taken enough care with the clues and testing this myself for these to have come out uniquely, but if not I'm sure one of my dearest readers will let me know soon enough.

Enjoy!
    #345 Signpost Sums Sudoku – rated easy(ish)
    #346 Signpost Sums Sudoku – rated medium

All puzzles © Tom Collyer 2009-20.

Tuesday, 23 June 2020

Leftover 2020 UKSC Puzzle

Here's a leftover puzzle from the 2020 UK Sudoku Championship.  I had thought to keep it in reserve for future years, but I think Sam has already seen it and he might want to take part.  Anyhow the reason this wasn't included was because Sam's puzzle was much better.  Not that this one is bad or anything though.  Enjoy!
    #344 Diagonal Sudoku – rated medium
All puzzles © Tom Collyer 2009-20.

Friday, 6 December 2019

Friday Puzzles #302

Here's a puzzle I don't believe I've posted publicly yet, but I think might be interesting to solve.  X-Sums Sudoku has some clues outside the grid indicating the sum of the first "X" numbers placed in cells in the corresponding direction, such that "X" is the number placed in the closest cell. For example an outside 3 means the numbers placed would be 2 followed by 1.

Enjoy!
    #343 X-Sums Sudoku – rated hard
All puzzles © Tom Collyer 2009-19.

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.

Enjoy.

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.

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

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.

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

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.

Enjoy!
    #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.

Enjoy!
    #338 Non-Consecutive Sudoku – rated medium
All puzzles © Tom Collyer 2009-17.

Friday, 10 March 2017

Friday Puzzles #296

Odd sudoku this week.  Only odd numbers are allowed in the shaded cells.

Enjoy!
    #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.

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, 8 January 2016

Friday Puzzles #289

Better late than never - and even better when the puzzle isn't broken - here is a Sum Sandwich Sudoku.

Rules: Apply classic sudoku rules.  Additionally, the clues outside the grid indicate all numbers placed in the corresponding direction that are the sum of the numbers placed in the two neighbouring cells in that direction, e.g. 132.  If a number is not clued outside the grid, then it must not be the sum of its two neighbours in that direction.

Enjoy!
    #328 Sum Sandwich Sudoku – rated medium
All puzzles © Tom Collyer 2009-16.

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