Calcudoku 6×6 puzzle

It’s been an age since I’ve posted new puzzles on here directly, mainly because all my puzzle-making effort has been focused on Sudoku Xtra, Sudoku Pro, PuzzleMix and a major book I recently completed.

In any case, there’s no time like the present to fix that so here’s a simple 6×6 Calcudoku. Just place 1 to 6 in each row and column and make sure the given number results when the stated operator is applied between the numbers in each bold region.

Issue 9 of my Sudoku Xtra magazine is now available for either download as a PDF, or pre-printed from Amazon.com (US) or Lulu.com (elsewhere). With an incredible 127 logic and number puzzles across over 50 types of puzzles, this month’s issue features a giant cover PivotPix picture logic puzzle (also known as Sym-a-Pix and Spiral Galaxies).

This issue has the biggest Community Puzzles section yet, with some truly astonishing puzzles contributed by the cream of the world’s puzzle authors. From Colorlink to a Hanjie-Nurikabe cross-over, and from Symmetric Heyawake to Lying Sum Sudoku, there’s something for everyone.

The rest of the magazine as always has some new variants and rearranged content in, including the interesting Killer Sudoku 1 3 5 7 9 -2 -4 -6 -8 (guaranteed to challenge even the best Killer solvers), Odd-Pairs S and more. With greater variety than any other puzzle publication, including a huge range of Sudoku variants, Sudoku Xtra really is incredible value.

Available from the Sudoku Xtra site now!

There’s an ‘S’ theme for a few of the puzzles this month, as you can see on the cover (right).

This issue I’m very excited to welcome some brand new Community Puzzles section contributors – Thomas Collyer, the two-time UK Times National Sudoku Champion; and Grant Fikes, one of the most prolific authors of Japanese puzzles outside Japan itself – who have very kindly donated some fantastic puzzles to this issue. There are also some brilliant Slitherlink/Sudoku cross-over puzzles by David Millar of The Griddle, and that’s only half of the section described so far!

The rest of the magazine as always has some new variants and rearranged content in, including Killer Prime (Killer Sudoku with prime numbers…) and Skyscraper S (a twisted 6×6 Skyscraper variant!). At just £3.99/$5.99 for a download it’s still incredible value even when compared to cheaper mags – with 116 puzzles that’s less than 4p/6¢ a puzzle, and you’d have to average around 4 a day to get the whole issue complete in time for issue 9!

With over 50 different types of puzzle in issue 8, what are you waiting for?!

Issue 51 of Sudoku Pro is on sale in independent newsagents now – you won’t find it in WH Smiths or your supermarket, but your local newsagent will be able to order it for you if they don’t already have it on the shelves. Or alternatively you can subscribe via the My Hobby Store website, and save some money and get it delivered to your door as soon as it’s available every month. At £22 for 12 issues it’s pretty amazing value. I have issue 51 in my hands and it looks as good as ever, now being in a slightly smaller and therefore more easily portable format.

If you enjoyed Sudoku Pro before then you’ll certainly enjoy it again, since the selection of puzzles is almost identical. If you’ve never read it but would be interested in a magazine packed full of Sudoku variants and other Japanese puzzles, then please do seek it out to ensure it sells enough issues to keep going strong!

Sudoku Xtra

Issue 7 of Sudoku Xtra contains even more large-page Japanese puzzle fun, with an incredible 116 varied logic and number puzzles. A special section in this issue is devoted to giant puzzles, with the 13 full-page puzzles including Hanjie, Nurikabe, Yajilin, Slitherlink, Hashi, Samurai Sudoku variants, Kakuro and more.

Sudoku Xtra offers greater variety than any other puzzle publication, with a huge range of Sudoku variants that include Jigsaw, Extra Region, Skyscraper, Consecutive and many more. Other featured puzzles include Calcudoku, Futoshiki, Hitori, Killer Sudoku and a range of variants, including Zero Killer Sudoku Inequality!

Designed to print on either A4 or Letter paper, or pre-printed on similarly large paper, Sudoku Xtra features puzzles at a range of difficulties, so is suitable for both logic puzzle fans and casual solvers alike. No matter what you like, you’re sure to find many puzzles to enjoy in Sudoku Xtra issue 7.

There’s also another great Puzzle Community section too, thanks to the generous contributors. Puzzles sent in for issue 7 include Navigrid, Mini Killer Sudoku, Knighted Sum Sudoku, Fillomino and more.

Get Sudoku Xtra 7 now.

Killer Plus Minus Samurai puzzle

If you’re a Sudoku Xtra reader you’ll have seen these in their regular 9×9 form in both issues 5 and 6, but this is the first time I’ve made a Samurai one, and the first time I’ve posted one here I think.

This is essentially a regular Killer Sudoku puzzle, except that instead of placing 1 to 9 you must place -4, -3, -2, -1, 0, 1, 2, 3 and 4 into each row, column and bold-lined 3×3 box.  There are also two overlapping 9×9 grids to solve simultaneously.

As in regular Killer, the values in each dashed-line cage must sum to the given total, and you cannot repeat the same number within any one cage.

Good luck!

It’s packed with a frankly ridiculous 133 separate puzzles. The range of content includes:

• Light-up / Akari
• A large cover Nurikabe puzzle
• -4 -3 -2 -1 0 1 2 3 4 Killer Sudoku – back by popular demand!
• A third Jigsaw 6×6 Variety Pack of miniature variants
• An extra-big Yajilin
• Killer Inequality Sudoku – lots of symbols on a grid!
• Dominoes - first time back since issue 1
• Plus all of the regular puzzles, from Skyscraper to Samurais to Calcudoku to Hashi to Hanjie to Kakuro and so on…

There’s a bumper-packed Puzzle Community section too, thanks to the generous contributors. Just look at some of the types that are in issue 6: 

• Yin Yang Sudoku
• Sudoku Minus (a trickier version of Sudoku Times!)
• Hexagon 25
• Klump
• Modula
• and more!

So if you’d like a copy (and if not, why not?! ) then just pick one of these links:

Download and self-print *  Lulu *  Amazon.com

Have fun!

Killer Sudoku Pro 6×6 Samurai puzzle

It’s been quiet here recently – much of my effort has been going on my UK General Election site, How To Vote, although Sudoku Xtra 6 was out on Saturday too.  Anyway, there are still 10 days to go to the election but after that I’ll get some time back!

However I thought I should finally post another puzzle – so here one is.  Place 1 to 6 in each row, column and 2×3 box (rows and columns are defined by the three underlying 6×6 grids, which you have to infer from the stepping).  Also place numbers so that the value at the top-left of each dashed-line cage results from applying the operation between all the value in that cage. For subtraction and division start with the largest value.

Have fun!

I’m very pleased to announce that issue 5 of Sudoku Xtra magazine is now available for download or in pre-printed form from either Amazon.com (US) or Lulu.com (recommended for rest of world).

This issue has even more puzzles than the previous ones, with a pretty mind-boggling 131 separate logic and number puzzles!

New content includes:

• Suraromu – the latest loop puzzle from Japan
• PivotPix (a.k.a. Tentai Show / Sym-a-Pix)
• -4 -3 -2 -1 0 1 2 3 4 Killer Sudoku!
• An extra page of Yajilin, designed to help you get into the puzzle
• Some new Sudoku combinations

Plus the regular stuff is there too, including:

• Another Jigsaw 6×6 Variety Pack of miniature variants
• More Sudoku at more sizes than ever before
• Lots of Sudoku variations on a theme
• All of the other regular puzzles, from Skyscraper to Samurais to Calcudoku to Hashi to Hanjie to Kakuro and so on…

And the generous puzzle community contributors have been as creative as ever. Just look at some of the types that are in issue 5: 

• Kuromasu / Kurodoko
• Sudoku Times (outside products)
• Hexagon 25
• Shapely Alleys and Skyscrapers
• Modula
• Pathfinder
• and more!

As always, it’s designed to print well in black and white on either A4 or Letter paper, using up most of the space and without pointlessly wasting ink on large dark areas. If you have a colour printer there’s a small colour trim to each issue – this month’s is orange – but this prints fine as a greyscale. Pre-printed copies have a colour cover but black and white interior.

So check it out!

And so now you can. If you play puzzles online at PuzzleMix then the statistics show a distribution of solution times, highlighting where you fitted:

My result is the yellow/pale blue bar, and as you can see I was the second or third fastest on this particular puzzle.  Previously all I’d have known is that I was better than average, and near the fastest. Now I can see just exactly where I fit in.

I think this is great! Of course, it’s a bit embarrassing when your highlight bar is off to the right, or doesn’t even fit on… (it only shows the top 90% of results when there are 20 or more, and omits all results longer than 2 hours).

Samurai 3-grid Calcudoku 6×6 puzzle

I’ve been posting a few new varieties of Sudoku puzzle in the daily puzzle section of PuzzleMix (i.e. the subscription section, which costs less than £1 a month for well over 1,000 puzzles a year). These aren’t especially unusual variations, but I’ve done a few different mixes (e.g. Sudoku-X 12×12 and Wraparound Sudoku 6×6), and I thought it was about time I posted a new mix here too.

So here’s a 3-grid Samurai Calcudoku puzzle.  You must place 1-6 in each of the 3 underlying 6×6 grids – I’m afraid these aren’t marked explicitly so you might want to draw in where the grid borders go so you don’t forget whilst solving.  Other than that, also place numbers so that the number given in each bold-lined cage results from applying the given operator between the numbers in that cage. Start with the highest number for division and subtraction. There is no restriction on repeating numbers in cages.

Good luck!

Toroidal Killer Jigsaw Toroidal puzzle

A while back someone asked for some variant toroidal patterns on PuzzleMix, so I was just adding a couple of them to the daily puzzles section when it occurred to me that I could put up a few toroidal killer sudoku too, for a change.  However I then realised that the code which creates the HTML will need editing to cope with toroidal regions, but I knew my PDF code was more flexible… and then I thought it would be great to mix this with some toroidal jigsaw regions too… and here’s the somewhat confusing result!  A Toroidal Killer with Toroidal Jigsaw regions.

Now if you enjoy this twisted beast let me know, otherwise I probably won’t make any more of them!

Full rules:

• Place 1 to 9 in each row, column and bold-lined jigsaw region
• Place numbers so that the dashed-line cages add to the total given
• No number can repeat in a dashed-line cage.
• Some jigsaw regions and cages ‘wrap around’ the outside the puzzle, continuing at the start/end of the same row/column

Good luck!

Samurai Star XXXXX puzzle

I haven’t posted a puzzle for a week (it’s been a busy week, mind!) so it’s time to make up for that, just in time for the weekend.

In this puzzle the aim is pretty simple: place 1 to 9 in each set of 9 squares starting and ending with a bold line, whether in a row or column, and similarly for each set of 9 squares starting and ending with a bold line in any of the shaded diagonals.

Good luck!

I picked 64 Killer Sudoku-X puzzles (52 for the daily puzzlemix section plus 12 for the weekly puzzlemix section), and of those about 5 or 6 (I didn’t write it down…) could be solved via reasonable logical deduction without using the ‘X’ diagonals.  So that’s roughly 10% of puzzles, if picked at random, that don’t need it.  Quite a bit worse than regular Sudoku-X (see previous post), but nowhere near as high a percentage as I’d expected – I had thought it could be 50% or more, although I should say that this isn’t actually a fair comparison because I disabled the cleverest maths-solving techniques from my analysis software. So in fact this is comparing clever Sudoku-X solving against the same Sudoku-X solving with the addition of relatively less clever Killer Sudoku-X solving, so perhaps this biased the result much more to the non-Killer result (from yesterday) than it should have done.  But anyway, I’m not writing a scientific paper and it’s good enough for me!

Killer Sudoku-X puzzleSo the result of all this is pretty simple: the Killer Sudoku-X on PuzzleMix for the coming year should be better than ever!  You should need that X every time…

PS Enjoy the Killer Sudoku-X I’ve attached here! Just place 1 to 9 in each row, column, 3×3 box and main diagonal, plus make sure the cages add to the given amounts – and don’t repeat a number in a cage.

Obviously a regular Sudoku has 9 rows, 9 columns and 9 boxes. Are we annoyed if we don’t “need” all 27 regions? Probably not. But in an ‘X’ puzzle I suppose it’s understandable that you’d expect to use the ‘X’.

Now of course there are different definitions of “needing” a region. Strictly-speaking, if you can prove a unique solution via any method (e.g. recursive search) without the regions then you don’t need them. But I decided to define “need” as meaning “you can’t solve the puzzle without them whilst using the standard solving techniques”. Standard techniques are those that Nikoli allow, so everything up to x-wings and hidden/naked quads.

Using this definition I looked at 100 randomly-selected Sudoku X puzzles of mine and found that 98 “needed” the diagonals, and only 2 didn’t.  Not bad! Of course this result will vary depending upon how vigorously you prune the number of ‘given’ digits in a puzzle.

It’s worth noting that not “needing” a region does not preclude it being useful – for example an easy Sudoku-X puzzle may happen to also be a very difficult regular Sudoku, so there is still value in including the regions even if they aren’t strictly-speaking essential. However there are enough Sudoku puzzle possibilities in the world that we can ignore this and simply select puzzles that don’t have any ambiguities.

Sudoku-X puzzle

So to celebrate, here’s a Sudoku X to solve. Just place 1-9 in each row, column, 3×3 box and the two main diagonals… but you know that already!

Next time I will look at Killer Sudoku X, but with the much heavier constraint of all the extra Killer regions I imagine the X will be needed far less of the time, thus the PuzzleMix comments. So I will be filtering my puzzles in future to make sure the X is always needed! I’ll also be filtering them for extra regions puzzles to make sure those are essential to solving them too.

Mind you, at the end of the day some people always find some puzzles easier than average just by making a fortuitous error – I’m sure we’ve all done it without realising! At those times there will always be puzzles that don’t seem to “need” the X…

Killer Sudoku Jigsaw puzzle

I’ve recently been working on refreshing the content for PuzzleMix.com, my play-online puzzle site, and one of the puzzle types I’ve been making is Killer Jigsaw Sudoku, where you not only have the jigsaw-shaped Killer regions but also jigsaw shapes instead of the regular 3×3 Sudoku boxes.

So I thought it would be a good idea to post one of these puzzles here – they can be quite tricky, at least until you get your head around the difference between these and regular Killer!

The rules are simple:

• Place 1 to 9 in each row, column and bold-lined region
• Place numbers in the dashed-line cages that add up to the given total for that cage
• No number can be repeated in a dashed-line cage

Good luck!

Samurai-2 Odd Pair Sudoku puzzle

One of the brand new puzzles in Sudoku Xtra issue 4 is Odd-Pair Sudoku, which I wrote about last week here on my puzzle blog. As well as some regular 9×9 puzzles I also included a large 5-grid Odd-Pair Samurai puzzle, and to illustrate how the puzzle worked I included a small solved example alongside. A full 5-grid Samurai was too big to fit sensibly in the example box, so I made a 2-grid Samurai version just for that little solution area. So that’s the solution used, but what about the puzzle itself? Well, here it is! (And so if you want to check your solution – yes, it’s printed in Sudoku Xtra issue 4! Page 19, to be precise).

The rules, in case you missed them, are really simple:

• Place 1 to 9 in each row, column and bold-lined 3×3 box of the two 9×9 Sudoku grids
• Every pair of squares with an ‘o’ circle between them must sum to an odd value. (’o’ for odd). So for example you could have “3 o 6″, but not “3 o 5″ (since that would sum to 8, an even number).

This variant is fun because it eliminates lots of possibilities from squares relatively quickly, so you’re left with more deductive logic and less pencil-mark housekeeping.

Good luck!

Issue 4 of Sudoku Xtra magazine is now with us!  I really think I might be putting too many puzzles into it, because typing up the list of content just knocked me out with how much is crammed into its 52 large-format pages!  Is too much possible?  I don’t know, but look at this enormous list:

128 puzzles in total, including several seriously giant ones.  Brand new for this issue:

• Samurai Star Killer Sudoku Pro
• Number Link Samurai
• Odd Pair Sudoku
• Samurai Odd Pair Sudoku
• Sudoku Inequality Jigsaw
• Jigsaw Sudoku 6×6 Variety Pack (including toroidal, inequality, X, consecutive and killer)
• Killer Sudoku Pro Jigsaw
• Sudoku 15×15 and Sudoku 18×18
• Killer Sudoku 15×15
• Odd & Even Pair Sudoku
• Killer Sudoku Prime

Regulars from issue 3:

• Hanjie
• Masyu
• Calcudoku (three times as many as in previous issues!)
• Slitherlink
• Consecutive Sudoku
• Hitori
• Samurai Star
• Samurai Star Jigsaw
• Number Link
• Jigsaw Sudoku 8×8, 9×9 and 10×10
• Toroidal Sudoku and Toroidal Inequality
• Kakuro
• Futoshiki
• Killer Sudoku
• Skyscraper
• Skyscraper Sudoku
• Samurai Sudoku
• SSSS: Skyscraper Samurai Star Sudoku
• Sudoku Inequality
• Sudoku Extra Regions
• Jigsaw Sudoku Extra Regions
• Killer Sudoku Jigsaw
• SOS: Samurai Outside Sudoku
• Outside Sudoku
• Sudoku 8×8
• Sudoku 12×12 and 16×16
• Samurai Extra Regions
• Yajilin
• Nurikabe

Adding to that already exhausting list still further are the community puzzles: 

• Heyawake
• King’s Journey (also known as Hidato[TM], Numbrix[TM] and many other names)
• Mosaic (Minesweeper picture puzzle)
• As Easy as ABC
• Knight’s Tour
• Shapely Skyscraper
• Isolate
• Klump

And all of this for just £3.99 or $5.99 – it really is fantastic value!

If you’d like to get hold of it just pop on over to the Sudoku Xtra website!

Samurai 8-grid Calcudoku puzzle

Here’s probably the largest Calcudoku puzzle you’ve ever seen!  It’s made up of 8 underlying 9×9 grids, each of which must have 1 to 9 placed into each row and column, and then on top of this I’ve added the familiar Calcudoku regions.

For each Calcudoku region just place numbers such that the total after applying the stated operation between the numbers in the region is the one given.  For example, 7+ could be solved by 3 and 4 (3+4). For subtraction and division start with the largest number in the region, so 1- could also be solved with 3 and 4 (4-3).

Just to make it really clear, there are no 3×3 Sudoku box regions in this puzzle – just the 8 sets of rows and columns.

Good luck!

Sudoku Odd Pairs puzzle

Now here’s something I can guarantee you won’t have seen before, because I just invented it! Well, I suppose with a world of people creating Sudoku variants it’s possible there’s been something similar before, but I’ve bought a lot of puzzle magazines and books and never come across it, so perhaps I should say I can just about guarantee you won’t have seen it before!

So the puzzle is Sudoku Odd Pairs, and as the name implies it’s all about odd pairs of numbers. Now you may have come across regular odd/even Sudoku before, and to be honest it’s a pretty dull variant (which is why I’ve never made them) – in fact if you for example shade all squares that contain even numbers it just breaks into two separate puzzles that overlap, and if you instead mark just a selection of even (or odd) squares then it’s only interesting until you work out whether the shaded squares are odd or even.

Sudoku Odd Pairs isn’t like that, because instead of marking squares what I’ve done is mark pairs of squares. Some squares have a grey circle between them – you can think of this as an O for Odd. What this means is that the sum of the solution of these two squares is odd. I don’t mark all odd pairs, however, because if you do this you need only one single digit in the entire grid (any of the givens will do) to work out which squares are odd and which even and then you end up with the above boring variant again.  So this is important: you can’t infer anything about squares without an O between them – only those with the O between.

It turns out (at least in my opinion!) that this is actually a really fun variant, because you end up with many interesting parts of each puzzle where you realise you can force sets of odds or evens into groups of squares (and not just those with the Os on), which in turn effect the rest of the puzzle. You do to an extent need to make pencil marks when solving, as in Consecutive and many other variants, but the nature of the constraint is such that the number of pencil marks is roughly halved relative to most other variants which (for me at least) makes it far more fun.

I’ve talked about it enough. Try out the puzzle here and let me know what you think!

And if you would like more of these, I’m putting them into Sudoku Xtra issue 4 (out soon!), including a nice Samurai version.