The Wide World of Sudoku


[A classic Sudoku grid with a colorful twist, where the 3×3 blue squares also have all 9 numbers inside them. One of many MANY Sudoku variants. Grid from]

For more than a century now, crosswords have been the premier pencil-and-paper (or pen-and-paper, if you’re confident) puzzle, but a close second would have to be Sudoku, which has exploded in popularity over the last decade or so.

The simple concept behind Sudoku — a 9×9 grid arranged so that the numbers 1 through 9 only appear once in each row, column, and 3×3 square — is easily modified for any difficulty level, from beginners to topnotch solvers.

The classic form of Sudoku, originally known as Number Place or To the Nines, is instantly recognizable.


[A Sudoku grid from PuzzleNation’s own free Classic Sudoku app for iPad.]

But virtually any set of nine different symbols, characters, numbers, or letters can be used as clues for a Sudoku-style solve. That gives us variations like Picture Sudoku or Color Sudoku, where the same deduction is involved, but the solution is a bit more vibrant.


[A color Sudoku from]

Word Sudoku follows the same concept, replacing the numbers 1 through 9 with letters, allowing for the added bonus of a 9-letter word reading out along one of the rows. I’ve seen Word Sudoku variations in all sorts of languages, which is neat, because you can still solve the puzzle even if you don’t know the language; you’re simply choosing different symbols.


[A Word Sudoku from Magic Word Square on Blogspot.]

Using letters instead of numbers often factors into larger Sudoku puzzles. While Penny/Dell’s Mega Sudoku is a 16×16 grid using the numbers 1 through 16, other large-scale Sudoku puzzles use letters instead of numbers above 10, while others go so far as to remove the numbers altogether, giving you the option of puzzles that span nearly the entire alphabet!


[A 25×25 monster Sudoku grid using letters, courtesy of]

And since we’re already discussing bigger Sudoku puzzles, it’s worth mentioning smaller Sudoku puzzles. Often called Mini-Sudoku or Sub-Doku, these puzzles start at 4×4 grids (using only the numbers 1 through 4) and increase in size all the way up to the standard 9×9 grid.

Those are just the puzzles that use standard Sudoku rules. There are numerous types of Sudoku that add new rules or curious wrinkles to the standard solve.

Perhaps the most famous variant is known as Extreme Sudoku, Diagonal Sudoku, or X-Sudoku, and there’s one crucial difference: the numbers 1 through 9 also appear only once along each diagonal. This additional rule helps with solving, but Extreme Sudoku puzzles often have fewer set numbers in order to keep the difficulty level interesting.


Another popular variation is known as Jigsaw Sudoku or Geometric Sudoku. These puzzles abandon the standard 3×3 boxes, instead using various Tetris-like shapes within the 9×9 grid. Each of these pieces contains each number 1 through 9, and the standard rule of no repeats within a row or a column remains.

These puzzles can either have random shapes or shapes with the same diagonal symmetry that rules both crossword grids and the placement of set numbers in classic Sudoku grids.


[A Jigsaw Sudoku grid from]

Some variations involve more deduction as well, like Neighbor Order Sudoku or Greater Than Sudoku. These puzzles feature small arrows that indicate whether the number in a given square is larger or smaller than its neighbor.

That’s just the start of math-based Sudoku variants that exist. Sum-Doku or Killer Sudoku uses the standard one-per-row, column, and 3×3 box Sudoku rule, but also adds numerous smaller Tetris shapes and boxes, each with a total. The numbers within that smaller box add up to that total.

Those totals are a crucial aid for solving, since Sum-doku puzzles often feature many fewer starting numbers. (The shapes of the smaller boxes often follow the diagonal symmetry of the set numbers.)


[A Sum-Doku grid from]

Another popular variant involves overlapping Sudoku grids. You could have two 9×9 grids that share one 3×3 box, or two 9×9 grids sharing four 3×3 boxes, or you could have more grids overlapping in all sorts of ways.


[A quadruple overlapping Sudoku grid, courtesy of the forums of]

The best known overlapping Sudoku puzzle is probably Samurai Sudoku, which features five 9×9 grids, one at the center and one at each corner, so the 4 corner 3×3 boxes of the center grid link the puzzle together.

Check out this masterpiece I discovered on


Not only is it a Samurai Sudoku with diagonal symmetry for all the set numbers, but each of the four corner grids operates under a different set of variant rules.

The upper left grid uses Extreme Sudoku (or Diagonal Sudoku) rules, the upper right grid is an asymmetric Jigsaw Sudoku (or Geometric Sudoku), the lower left grid has shaded the location of every even-numbered number to aid your solving, and the bottom right has two shaded ribbons weaving throughout the grid, each of which also includes each number from 1 through 9 once.

As you might expect, there are plenty of variations of Samurai Sudoku. My personal favorite is known as Shogun Sudoku; it’s two linked Samurai Sudoku grids — meaning there are ELEVEN linked 9×9 grids — and there are even larger variations out there for the solver who simply can’t get enough of overlapping Sudoku puzzles.


[Upper left: Tight Fit Sudoku, Upper Right: Thermo Sudoku,
Lower Left: Arrow Sudoku, Lower Right: Consecutive Sudoku.]

Our friends at Penny/Dell Puzzles have several titles that offer a variety of different Sudoku puzzles. The four grids above all appear in various issues of Will Shortz’s WordPlay, all courtesy of Sudoku constructor Thomas Snyder.

You should also check out the Sudoku Spectacular title (featured in our Holiday Puzzly Gift Guide!) as well as their upcoming Will Shortz’s Sudoku title.

I would also be remiss if I didn’t mention the mathier cousins of Sudoku.


Kakuro, also known as Cross Sums, follows the same no-repeats rule of classic Sudoku, but the grids are much closer to Crosswords. The numbers along the top and left-side are the total for each row or column, and they are the primary clues for solving the puzzle. Kakuro rarely features set numbers the way Sudoku does, instead opting for a single filled-in row or column to get the solver started.


[A 6×6 KenKen grid, courtesy of The Math Magazine on Blogspot]

KenKen takes the addition from Sum-Doku and adds subtraction, multiplication, and division to the mix. Each box has a number and a mathematical symbol. The number is the total, and the symbol is how the missing numbers interact to reach that total. For instance, in the upper right corner of the grid, there’s 24X. That means the two missing numbers from that box, when multiplied, equal 24.

And since this is a 6×6 grid, following the same one-per-row and column rules of Sudoku, you know that 4 and 6 are the missing numbers in that box, but you don’t necessarily know where to place them yet.

When it comes to Sudoku, the variations on shapes and layouts are seemingly endless. I’ve seen diamonds and snowflakes, cubes and five-pointed stars, in all sorts of sizes. You can get Samurai Sudoku with 6×6 grids, Jigsaw Sudoku in miniature, and Word Sudoku with Egyptian hieroglyphics.

While researching this post, I encountered this marvelous Sudoku variant, which the constructor calls Star Sudoku.


The numbers 1 through 9 appear once in each triangle, and there are no repeats along any row or slanted column. This puzzle is not only clever, it’s flat-out neat.

So, fellow puzzlers, what’s your favorite variation of Sudoku? Or do you prefer to stick with the classic version? Let me know! I’d love to hear from you!

Thanks for visiting PuzzleNation Blog today! You can share your pictures with us on Instagram, friend us on Facebook, check us out on TwitterPinterest, and Tumblr, and be sure to check out the growing library of PuzzleNation apps and games!

Wait a Minute, Mr. Postman…

With subscriptions to puzzle magazines like Will Shortz’s WordPlay and GAMES Magazine, as well as puzzle-by-mail services like The Uptown Puzzle Club and The Crosswords Club, there are plenty of ways to get puzzles by mail.

But one particular puzzler in the UK has put an intriguing twist on the idea of puzzles-by-mail: he’s challenged the carriers of the Royal Mail postal service to solve puzzles in order to deliver his mail.

A graphic designer by trade, James Addison was impressed by the diligence of the postmen of the Royal Mail, and he playfully decided to test their mettle with different challenges, including maps, word searches, pictograms, and other befuddling methods to conceal the intended destination of the letter.

From an article on The Telegraph website:

Although he enjoys solving puzzles himself, he said his hobby was fuelled by a desire partly to test the Royal Mail’s ingenuity and partly to honour old-fashioned letter-writing, following his mother’s advice that a handwritten thank-you note showed you had made an effort.

Well, Mr. Addison is certainly taking his mother’s words to heart. And it seems the postmen of the Royal Mail quite enjoy the spirited challenges his letters offer.

[To try your hand at solving some of Jim’s letters, including those pictured in this post, click here!]

Thanks for visiting PuzzleNation Blog today! You can share your pictures with us on Instagram, friend us on Facebook, check us out on TwitterPinterest, and Tumblr, and be sure to check out our library of PuzzleNation apps and games!

5 Questions with Constructor Trip Payne

Welcome to another edition of PuzzleNation Blog’s interview feature, 5 Questions!

We’re reaching out to puzzle constructors, video game writers and designers, board game creators, writers, filmmakers, musicians, and puzzle enthusiasts from all walks of life, talking to people who make puzzles and people who enjoy them in the hopes of exploring the puzzle community as a whole.

And I’m excited to have Trip Payne as our latest 5 Questions interviewee!

A freelance puzzle constructor for over twenty years, Trip Payne is one of the most prolific and respected names in puzzles. A multi-time champion at the American Crossword Puzzle Tournament, he’s been published in The New York Times, The Wall Street Journal, Uptown Crossword Club, GAMES Magazine, Will Shortz’s WordPlay, and numerous other outlets.

On August 1, he’s launching his latest Puzzle Extravaganza, a collection of a dozen different puzzles (plus a special metapuzzle) for only $10! Previous extravaganzas have featured themes like the 2011-2012 television season and the Man of Steel himself, Superman, but this year’s theme is a closely guarded secret! Check out the details here, including an offer for three bonus crosswords!

Trip was gracious enough to take some time out to talk to us, so without further ado, let’s get to the interview!

5 Questions for Trip Payne

1.) How did you get started with puzzles?

As a very young child, I was attracted to the black-and-white crossword patterns, and my parents noticed that interest and bought me children’s puzzle books. I was always into riddles, magic, games — everything sort of related to puzzles.

Eventually I started coming up with puzzles for my elementary and junior high school newspapers, and when I was 15 I had my first puzzle published nationally in GAMES Magazine.

2.) What, in your estimation, makes for a great puzzle? What do you most enjoy — or try hardest to avoid — when constructing your own?

In terms of crosswords, my #1 rule has always been: It’s All About The Fill. Of course you want a great theme and clever clues, but the second you resort to weak entries, you’ve lost my interest. A lot of people are willing to “justify” weak entries because they’re “necessary” to pull off a wide-open grid or an ambitious theme; I don’t agree with that. With enough work, and perhaps a willingness to pull back a little from the original concept, you can pretty much always avoid poor fill.

Look at Patrick Berry: his themes are great, and you’d have to inspect his puzzles with a microscope to find a weak entry anywhere. That’s not magic — he just has high standards and a willingness to put in the work to make his puzzles as good as they can be.

A great puzzle is one that gives a satisfying “a-ha” at some point, that makes the solver glad that they’ve invested the time with it.  In a logic puzzle, it may be some clever leap that has to be taken; in a word puzzle, it may be an interesting anagram or misleading clue; it may be on a larger scale, as when you discover how the answers to various puzzles interact to solve an overall “metapuzzle.” 

3.) You’re a three-time American Crossword Puzzle Tournament champ and a perennial top 10 finisher. How does tournament solving differ from regular solving, and do you think your experiences with game show environments (like Who Wants to Be a Millionaire?, Million Dollar Password, and Scrabble Showdown ) helped you thrive in the ACPT?

Well, not perennial, since I retired in 2011 (though I did compete one final time in Lollapuzzoola in 2013). My game show work all came after my ACPT championships, so there was no real connection there. But I do think that the fact that I was a professional puzzlemaker before I started competing in puzzle tournaments helped me; for one thing, you get a sense of letter patterns and a feel for how a puzzle constructor might have filled a corner.

4.) What’s next for Trip Payne?

I’m currently editing the Daily Celebrity Crossword for PuzzleSocial, and I have a few other regular assignments, such as the “wordoku” in TV Guide and my themeless crosswords for the Washington Post Puzzler.

I plan to continue making my annual extravaganzas and hope to completely overhaul my website,, within the year. And I also hope to continue doing work writing and researching for TV game shows, and perhaps pitching my own game show ideas to producers.

5.) If you could give the readers, writers, and puzzle fans in the audience one piece of advice, what would it be?

Enjoy the puzzles that you love, but experiment: there are all sorts of great innovative puzzles out there, and you might be surprised what you end up enjoying.

Also, buy my puzzle extravaganza!

Many thanks to Trip for his time. Check out his website for links to all his puzzly endeavors, and be sure to follow him on Twitter (@PuzzleTrip) for the latest updates on his many irons in the fire! Can’t wait to see what puzzle fun he conjures next.

Thanks for visiting PuzzleNation Blog today! You can share your pictures with us on Instagram, friend us on Facebook, check us out on TwitterPinterest, and Tumblr, and be sure to check out the growing library of PuzzleNation apps and games!

5 Questions: Alumni Edition

Undoubtedly one of the most popular features on the blog in 2013 was 5 Questions, our interview series featuring puzzle constructors, authors, filmmakers, game designers, puzzle enthusiasts, and creative people in general whose work and play relates to puzzles.

As 2013 was winding down, I reached out to our 5 Questions alumni to catch up and ask them what they’d been up to since appearing here last. (Or when I’m not pestering them for crossword construction advice or New Year’s Resolutions. *laughs*)

And so many of them were happy to share their latest projects with the PuzzleNation audience!

Author Robin Sloan’s marvelous novel Mr. Penumbra’s 24-Hour Bookstore is out in paperback, and the prequel story Ajax Penumbra 1969 is available as an eBook. I asked him about what he’s been doing, and his answer was brief and exciting:

Let’s see… I’m hard at work on a new novel!

That’s about it 😀

Can’t wait to see what he’s got in store for us next.

[Click here to check out Robin’s session of 5 Questions, as well as our book review of Mr. Penumbra’s 24-Hour Bookstore here.]

Great Urban Race Senior Manager Jordan Diehl was also happy to bring us up to speed on what the GUR crew has been up to:

We just finished a successful Championship event in San Juan, Puerto Rico. It was our first time outside of the continental US, and the race was really well-received. Like in years past, a total of $10,000 was given out, but this year it was divided among the top 8 teams as opposed to years past where only first place received cash prizes.

The division of prizes will remain as we enter our 2014 season:
First place: $6,000
Second place: $2,000
Third place: $1,000
Fourth – Eighth place: $200 each

And speaking of, we are excited that our 2014 season is just around the corner!

We’ve consolidated our schedule for 2014; our first event is in late January and the last regular-schedule event of the season will be June 7. This leaves us room for another new Championship location in a potentially colder climate that we could not typically do in November/December (the usual dates of our Championship) as we are looking at an August/September Championship date.

Here at Great Urban Race, we’ve decided that 2014 is the “Year of You,” and we are focusing on listening to participant feedback more than ever. We put out a vote for Championship locations as well as several other campaigns like it through our social media pages.

[Be sure to check out the Great Urban Race website for more details, and click here to read Jordan’s session of 5 Questions.]

Kathy Matheson (a.k.a. puzzle blogger Crossword Kathy) had some interesting news to share, not only regarding her puzzle-constructing aspirations, but interacting with the PuzzleNation readership as well!

After the 5 Questions interview appeared, I was pleasantly surprised to get feedback from a couple of your readers! One is a fellow journalist here in Philly — I recognized his byline but have never met him, and didn’t know he was a puzzler, too. He told me about a local constructor he interviewed a few years ago, when she was 95! Now she’s about to turn 100, and he said she’s still making crosswords. Amazing. I hope to write a story about her myself, somehow tying it in to the just-passed centennial of the crossword.

The other person who contacted me is a constructor I admire who very kindly offered to help with my grid-building dreams. Part of me really wants to take him up on the offer, but part of me is very independent and wants to do it alone.

The truth is that I haven’t spent as much time constructing as I should, so perhaps I should do more of that before asking for help. I did send the L.A. Times one of my puzzles, which was rejected by a very nice note saying that “there’s some good work in your grid, but the theme puns are too stretchy” for their taste. Oh well.

[I have no doubt we’ll be seeing Kathy’s name in a puzzle byline in 2014. Click here to check out her session of 5 Questions!]

Puzzle poet Peter Valentine regularly posts his latest creations on Twitter and Tumblr — I’ve posted his poem “Birthday” for the 100th Anniversary of the crossword above — and has recently added another social media platform to his arsenal.

I’ve started an instagram feed, @peterboothby, which helps to reach many more folks and generate discussion.

[You can check out the full archive of his poems here, as well as his session of 5 Questions here.]

As you might’ve expected, constructor and puzzle historian David Steinberg has kept himself very busy between his own crossword construction and his work on the Pre-Shortzian Puzzle Project, which recently passed the 14,000 puzzle mark!

On December 21, the crossword centennial, I gave a talk at the Palos Verdes Peninsula Center Library on crossword history, the Pre-Shortzian Puzzle Project, and crossword editing, solving, and constructing. Also, I constructed a special centennial puzzle for the Focus page in The Orange County Register.

[Check out The Orange County Register, where David serves as crossword editor, as well as his session of 5 Questions here.]

Prolific constructor Robin Stears has been puzzling up a storm since last we spoke.

The dust has settled from the 100th anniversary celebrations, and of course, the other holidays took up some time, but I’m ready to get back to work. My daughter took pity on me and spent a day fixing my Tumblr blog so that it’s easier to find, sent out messages to all my Tumblr followers, and helped me set up a Tumblr-exclusive giveaway (to make up for my ineptitude). She even tweaked it for the holidays!

I’m starting off the year with a 21×21 StearsWords puzzle entitled “Things to Look Forward to in 2014.” There’s so much to look forward to, it needed a giant-size puzzle.

The Trivia Challenge puzzles seemed to be popular, so there will be more of those. I’ll continue to invite social media fans to send me their ideas and watch them come to life–a Reddit fan suggested “Doctor Who,” a Tumblr fan is responsible for the “Game of Thrones” puzzle, and a Facebook fan challenged me to do a “420” puzzle; clearly, I’m open to just about anything. (Someone asked me to do a cryptogram/crossword, where solvers have to decipher the clues, and then solve the puzzle. It sounds like a lot of work, but also a lot of fun; it also sounds perfect for a contest.)

Naturally, I’ll be keeping a close watch on what’s hot, just in case there’s another “Sharknado”-like event that begs to be immortalized in crossword. And solvers will still find the majority of my work in Penny/Dell puzzle books. They’ve been printing my puzzles for over twenty years, and I’m a huge fan of their puzzle books, as evidenced by the ginormous stack of Good Time Crosswords in my office.

[You can also join Team StearsWords by clicking here, and check out her session of 5 Questions here.]

As you might expect, David L. Hoyt has been busy. The most syndicated man in puzzles continues to produce his signature Jumble puzzles, but he also has a new puzzly product to share.

Just 2 Fun (pictured above) is David’s latest creation and his first app for younger players (ages 9 and up). The app is available for iPad, iPad mini, iPhone 4 and 5 and iPod touch devices. Just 2 Fun is a kids’ version of the enormously successful puzzle app Just 2 Words.

[You can explore all of David’s puzzly creations on his website, and check out his session of 5 Questions here.]

Even our latest interviewee, New York Times crossword editor Will Shortz, had something to share with us in the few weeks since appearing on the PuzzleNation Blog.

You may recall him mentioning his favorite pastime:

At the moment I’m close to finishing a personal goal — to play table tennis every day this year. As I write this (on Dec. 17), I’ve played every single day since Jan. 1 — 351 days in all.

I’m happy to report that Will did in fact complete his 365 days of table tennis for 2013, even throwing a party to celebrate. (I suspect New Year’s Eve may have also contributed to the festivities.)

[Check out Will’s contributions to NPR’s Weekend Edition here, as well as his session of 5 Questions here. We hope to have more information on his new puzzle magazine Will Shortz’s WordPlay very soon.]

Thank you to all of our 5 Questions alums! They helped make 2013 a banner year for PuzzleNation Blog, and as we head into 2014 with new interviews to come, I promise to keep you posted on everything these brilliant puzzly folks are up to.

Thanks for visiting the PuzzleNation blog today! You can like us on Facebookfollow us on Twitter, cruise our boards on Pinterest, check out our Tumblr, download our Classic Word Search iBook (recently featured by Apple in the Made for iBooks category!), play our games at, or contact us here at the blog!