# The UK Sudoku Championship! (Or should that be Sudo-UK?)

Hot on the heels of The Indie 500 crossword tournament last weekend, the UK is also gearing up for a major puzzle event: The UK Sudoku Championship!

The event spans June 10 through June 13, and chairman Alan O’Donnell of the UK Puzzle Association sent out the Instruction Booklet for this year’s event a few days ago, which kicks off a string of major puzzle events in Europe and across the world, including the UK Puzzle Championship in a few weeks.

Although the UK Sudoku Championship is only open to competitors from the UK — with the top two earning a place on the UK team for the 2016 World Sudoku Championship — international players are welcome to test their puzzly mettle as guest solvers.

But even if most PuzzleNationers aren’t eligible to compete, you can still enjoy the challenge of some topnotch Sudoku puzzles. Let’s take a look at some of the diabolical puzzles they’ve cooked up for this year’s event!

[An Extra Regions puzzle, a variation on Classic Sudoku.]

In addition to some Classic Sudoku, Extreme Sudoku, Sum-Doku (or Killer Sudoku), Jigsaw Sudoku (or Geometric Sudoku), and Thermo Sudoku — all of which I explored in detail in my Wide World of Sudoku post — there are some variants I’ve never seen before, like this Linked 6×6 Sudoku.

In this puzzle, you have two grids to complete, but with the additional wrinkle that no number placed in the left 6×6 grid will occupy the same square in the right 6×6 grid. So you have more solving information than expected, but it’s spread out across two grids.

This Deficit Sudoku puzzle also uses the 2×3 box format, but arrayed in a 7×7 grid. This means that any of the numbers 1 through 7 can be in each 2×3 grid, which makes it slightly harder than if you were only using the numbers 1 through 6.

(Plus you have no information on what number goes in that solo square in the center of the grid.)

The curiously named Odd-Even-Big-Small Sudoku employs clues outside the grid to help you fill in some of the squares along the perimeter of the grid, telling you that two odd numbers, two even numbers, two small numbers, or two big numbers will occupy the nearest two spaces in that row or column.

This is a solving mechanic I’ve never encountered before in Sudoku, and I can see it posing an impressive challenge to the average Sudoku solver.

That unconventional style of cluing sets the tone for the rest of the unusual puzzles that competitors and solvers will encounter here. In the above grid, a Consecutive Pairs puzzle, those dots indicate that the neighboring numbers connected by those dots are consecutive numbers, like 5 and 6 or 2 and 1.

(You can also try Consecutive Pairs Sudoku in Will Shortz’s Sudoku and Sudoku Spectacular, both published by our friends at Penny Dell Puzzles.)

XV Sudoku works in similar fashion, with x’s and v’s instead of those little dots. The x’s mean the neighboring numbers add up to 10, and the v’s mean the neighboring numbers add up to 5.

This Eliminate Sudoku uses arrows to indicate that the number in the arrow box will not be repeated in any of the boxes that follow that arrow. So, for instance, if you place a 3 in that arrow box next to the 2 in the upper-right 3×3 grid, none of the boxes that arrow points at along that diagonal will contain a 3.

Like the dual grids in the Linked 6×6 Sudoku, this puzzle is interesting in offering more information on what’s NOT in a square than what IS.

The final new puzzle in the Instruction Booklet is my favorite, but that’s because I’m a sucker for palindromes in puzzles. This Palindrome Sudoku features gray lines that indicates spots where — you guessed it! — the chain of numbers reads the same backwards and forwards.

Similar to Thermo Sudoku in its solving style, Palindrome Sudoku takes advantage in the restrictive nature of Sudoku solving by adding a neat little twist.

You can check out the full Instruction Booklet here, and remember to keep your eyes peeled on June 10 when the actual puzzles go live!

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# The end of Sudoku?

I recently read in Owen O’Shea’s book The Call of the Primes that there are 5,472,730,538 unique solutions for a 9×9 Sudoku grid.

Yes, five billion is a very big number, but these days, billions aren’t what they used to be. I mean, think about how many newspapers, magazines, and puzzle books feature Sudoku puzzles. It’s a huge amount of material every year.

So, the thought occurs to me…how long before those 5,472,730,538 unique solutions run out?

To be fair, it’s not like reaching Peak Oil or a point of no return. I’ve solved a lot of Sudoku puzzles, and never once have I felt like I was re-solving a grid I’ve seen before, even if I was. This is purely a matter of mathematical curiosity. How long would it take for us to use up every last possible 9×9 grid?

Man, where do I begin?

Well, if I’m going to talk Sudoku puzzles, it makes sense to start with our friends at Penny Dell Puzzles.

Across seventeen Sudoku titles, they publish approximately 23,236 Sudoku puzzles a year, and probably an additional 350 per year across their Crossword/Variety and Variety titles for a total of 23,586 puzzles in a calendar year.

Now, Penny Dell Puzzles is the top puzzle publisher in North America — #humblebrag — and let’s assume there are another half-dozen publishers worldwide matching their output. That gives us a ballpark of 165,100 Sudoku puzzles published worldwide.

According to the Newspaper Association of America, there were 1,331 daily newspapers in 2014, and there were 1,450 daily newspapers in 2005, making an 8.2% decrease from a decade before. If we apply that percentage to the number of daily newspapers worldwide as of 2005, 6,580 titles, we get 6,040 daily newspapers worldwide. And although they may not ALL have a daily Sudoku, this will help cover some of the major magazines that also carry Sudoku that I’ve excluded from my ballpark calculations.

That gives us 6,040 newspapers x 365 puzzles a year for a total of 2,204,600 puzzles a year.

Now, for other publishing efforts regarding Sudoku, Amazon.com lists 20,718 results for Sudoku, and if we apply an average of 217 puzzles per title — which seems a fair approximation, based on the stats published by our friends at Penny Dell Puzzles, the fact that some books will have more puzzles, and some results will be ABOUT Sudoku and probably contain few to none actual puzzles — that’s 4,495,806 puzzles available right now in the world’s biggest bookstore. (Yes, obviously not all of them were published this year, but hey, this is meatball mathematics.)

Unfortunately, statistics on Sudoku are sketchy at best for the mobile app market, online puzzling, and downloadable puzzles through Playstation Network, Wii, and other gaming platforms, so I can’t factor those puzzles into my calculations.

But just with the numbers I’ve got here, we’re talking about 6,865,506 Sudoku puzzles worldwide. So, if each of those Sudoku puzzles is unique — which is possible, if unlikely — that barely makes a dent in our total of possible Sudoku grid layouts, which you recall is 5,472,730,538.

So, if we’re producing 6,865,506 unique Sudoku puzzles a year, it’ll take nearly 800 years to use every possible 9×9 grid! (For the folks at Penny Dell Puzzles, it would take nearly 232,033 years! So they’re in the clear. *laughs*)

I guess we won’t be running out anytime soon.

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# Sudoku Around the World!

Sudoku is the most popular pen-and-paper puzzle since the crossword. No other puzzles come close. Whether it’s in your local paper, our iPad app, or one of the magazines offered by our friends at Penny/Dell Puzzles, chances are you’ve solved a Sudoku puzzle at one time or another.

And the solving experience is an integral part of its success. When you look at a Sudoku grid, you instinctively know what sort of puzzle you’re dealing with and what the goal is. You don’t need the instructions or any elaborate explanations. You can simply dive right in.

That sort of simplicity and accessibility gives Sudoku major appeal, and has contributed to its success as an iconic puzzle worldwide.

Look at this stack of puzzle books from around the world, loaned to me by a friend of the blog!

There are Sudoku books in Russian, French, Japanese, and other languages! And yet, you could pick up any one of these magazines and start solving immediately.

Here are two Samurai Sudoku from a Russian puzzle magazine. Again, these are identical to the overlapping grids you find in the States.

I did, however, encounter a few intriguing variations I was unfamiliar with as I perused these magazines published by 777.

Instead of providing sums in smaller boxes within the grid like Sum-Doku puzzles, or along the edges like Kakuro, these puzzles offer totals that correspond to the three diagonal boxes in a line a given arrow points to.

In this Sudoku variant, there are no repeats of the numbers 1 through 8 in a given row or column, but there are also no repeats within each group of connected circles.

Again, although I couldn’t read the instructions for these new puzzles, I was easily able to figure out the mechanics of each and start solving within a few minutes. Very few puzzles have that sort of universal accessibility.

While I’m very familiar with Kakuro (or Cross Sums) puzzles, I’ve never encountered cut-style grids like these. I just love the simple elegance of these diamond-shaped grids. Very eye-catching.

Believe it or not, this is just a sampling of the hundreds and hundreds of Sudoku magazines and puzzle books released over the last decade.

Although the puzzle as we know it has been around since the ’70s under other names (To the Nines and Number Place, among them), it was only relatively recently that it exploded in popularity, becoming a true cultural touchstone and undeniable puzzle phenomenon.

[For another blog post exploring puzzle books from around the world, click here!]

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