Cognitive Daily

What will be the next Sudoku?

i-50ec28b39d618cfa29dc6f680746d48a-kakuro.gifThe New York Times has a great article on the Japanese gaming company responsible for the Sudoku craze. The article is interesting, but be sure to check out the sidebar, where you can try three up-and-coming rivals to Sudoku.

Personally I find Sudoku a little boring: After I figured out a “system” that allowed me to work out almost any puzzle, it just doesn’t offer much challenge. So what’s next? I really like Kakuro, which has actually been around for a while (I can even remember its U.S. version from the 1970s: “Cross-Sums”). You can try the sample puzzle on the New York Times page, but the Washington Post has a much better interface and a new puzzle every day. Puzzles are rated for difficulty, with one star being very easy and four stars sometimes practically impossible. Usually the more difficult puzzles come at the end of the week. I’ve never seen a five-star puzzle.

I had never seen the other two examples on the New York Times site: Masyu and Nurikabe. Both games are excellent. Nurikabe is intriguing, but I wonder if it will end up being a bit too easy in the long run, much like Sudoku.

i-1cb4673c7255cbb5c053baa9dd73221c-kakuro2.gifMasyu is simply fascinating. The goal is to draw a line — a loop that connects back to itself — through all the circles in the square. Each circle has different “rules” — a line through a black circle must be a corner, and a line through a white circle must be straight. The line approaching and leaving black circles must be straight, and one or both of the lines approaching white circles must be corners. Can you see why my partial solution won’t work?

This is the sort of game that comes with many “brain fitness” products, so arguably playing these games isn’t just a time-waster, but also something which helps improve mental ability.

Do you know of other fun puzzle games? Good online sites for the games listed above? Let us know about them in the comments.


  1. #1 Tara
    March 22, 2007

    My favorite is Slitherlink (aka Number Line, Fences, Kwon-Tom Loop, etc) because there are an unlimited number of patterns you can discover. I actually first saw it in some old qualifying tests for the World Puzzle Championship (a great source for a wide variety of challenging puzzles).

  2. #2 BlogReader
    March 22, 2007

    CrossSums are the only reason I pick up Dell crossword magazines (their Medium puzzles are way too easy and the Hard ones are near impossible for me).

    I don’t think CrossSums will catch on like Sudoku as CS requires a lot more planning ahead than Sudoku, which people can do in their sleep.

  3. #3 Craig Helfgott
    March 22, 2007

    Try Nikoli’s subscription-only puzzle website, $5 a month, you get ~2 puzzles a day.

    I like SlitherLink, and there’s one in their magazine whose title translates to “Ripple Effect” which drives me buggy.

  4. #4 Maeve
    March 22, 2007 is a great site for a selection of different puzzles, including Japanese puzzles like Sudoku, Hitori and Bacarba. At my last check they had over 4000 puzzles. There should be enough to satisfy everyone there.

  5. #5 Dave Munger
    March 22, 2007

    I just tried the slitherlink sample at You may have gotten me hooked…

  6. #6 Dr. Barnardo
    March 22, 2007

    Hanjie is another good one. I think it can also be called “Piccross” or “Paint by Numbers”. It combines logic with a little bit of art. I have never seen a website with good puzzles on it though.

  7. #7 qetzal
    March 22, 2007

    Re Hanjie,

    Try Conceptis Puzzles. They call them Pic-a-Pix, and have quite a few samples that can be downloaded. Unfortunately, they show the completed pictures on the page where you download them, which takes away some of the challenge.

    Games Magazine also runs 5-6 of these in every issue.

  8. #8 Coin
    March 23, 2007

    I actually was playing Nurikabe before Sudoku hit, and I still like Nurikabe better, I think. I never got really into the very high levels of Nurikabe, but I got into it more than I got into Sudoku, and it never got that repetitive/algorithmic feel that Sudoku gets after awhile.

    So lately I’ve been looking into loop quantum gravity, just for the amusement of trying to understand it. While I still don’t understand a single fricking thing that’s going on, I’m becoming increasingly convinced that someone who did understood the rules of the thing could design a really great game out of LQG loop diagrams or spin networks. I’m amused by the idea of a vaguely Nurikabe/Masyu type game that is playable by an average person, but anyone who plays it is solving advanced lie algebra problems without even knowing it.

    Hanjie is another good one. I think it can also be called “Piccross” or “Paint by Numbers”. It combines logic with a little bit of art. I have never seen a website with good puzzles on it though.

    I don’t suppose you have a Nintendo DS? There’s a “Picross DS” game that’s apparently about the greatest thing ever on that front, including some kind of multiplayer and the ability to download new levels off the internet. You have to import it from Japan, but there’s a crop of excellent websites that let you do that sort of thing at reasonable prices now; I know a bunch of people who’ve imported Picross DS and they’ve indicated there is not a language barrier.

  9. #9 Pierre de Vries
    March 23, 2007

    What makes a hard puzzle hard? Puzzles are rated for difficulty (one to four stars); some people are clearly better than others at puzzle solving, and experience helps. But there’s a limit to human cognitive capacity; as Dave said, “I’ve never seen a five-star puzzle.” What’s the basis for this limit? Do different puzzles push up against different cognitive barriers?

  10. #10 Dave M
    March 23, 2007


    That should keep you busy for a while (in German, but don’t let that stop you).

  11. #11 Nick
    March 24, 2007

    I ran across, which puts out (free!) sudoku variants — the hardest I’ve ever seen. Some of the vocabulary used there may be unfamiliar (know what a “cage” in a “killer sudoku” puzzle is?), but it’s easy to pick up.

    As an example, try this out: it’s five overlapping 9×9 grids, each of which has a different set of rules that must be followed for number placement.

  12. #12 paul curran
    March 24, 2007

    I was playing Sudoku long before it was ever called that, as well as Cross Sums. Why is that we have to send things to Japan and then have it sent back here under a differnt name in order to make them popular?

  13. #13 Ginger Yellow
    March 25, 2007

    The Guardian started doing Kakuro puzzles at the peak of the British media’s Sudoku-mania (“look at us, aren’t we clever?”). It’s more stimulating than Sudoku, but I’ve gone off both since podcasts took off and I bought a Nintendo DS. Between those and the cryptic crosword I’ve got more than enough to occupy my commute.

  14. #14 armando
    June 25, 2007

    For everybody who wants to try out something new in sudoku, try shendoku, using the sudoku rules but playing two people, one against the other, like battleshipps. They have a free version to download at . Anything else they are bringing out or they are working on you can find at or at they┬┤r blog . Have fun, I am. I specially like one slogan I heard about Shendoku: SUDOKU is like masturbation (one person)…. SHENDOKU is like sex (it takes two).

  15. #15 Armando Garcia
    April 15, 2009

    I love Str8ts. Nothing that I have tried is a nice as this puzzle. If anything can compete with Sudoku. This one should be the front runner. They have daily on line puzzles.

  16. #16 M.Schwartz
    September 13, 2009

    Thanks Armando for pointing out Str8ts. I never heard of the puzzle until this post. I didn’t expect a lot, but I am with you it is by far the best puzzle besides Sudoku. I am playing it on my iPhone when i am on the go. Amazing concept.