Like Sudoku?

| 10:41 UK time, Wednesday, 13 June 2007

Chris Hogg, our top man in Tokyo, has a piece for you tonight. Not only can we bring you pictures of some of the people who're in it - but a BRAND NEW type of puzzle for you to try. This chap is

the self-styled father of Sudoku, Maki Kaji (it's written on his business card so it must be true). He found the puzzle in the USA and published it in his quarterly puzzle book. He sells 50,000 copies of each edition.

This is the vice president of Japan's Mathematical Association Tsuneharu Okabe. The square thing is a puzzle one of his students has invented. You are supposed to be able to turn it inside out so that there is only one colour showing. Chris writes: "As you can see

he tried to show me how to solve it - but of course I was rubbish. I failed Maths A-level and it showed."

"This is computer programmer Nobuyuki Sakamoto posing proudly with one of the puzzles he has submitted to Kaji-san's magazine and had published. Trust me in the world of Japanese puzzle making that is about as good as it gets …"

Now: here is a puzzle from the Japanese publishers who made Sudoku famous.

It is called Masyu.

These are the rules:

Make a single loop with lines passing through the centers of cells, horizontally or vertically. The loop never crosses itself, branches off, or goes through the same cell twice.
Lines must pass through all cells with black and white circles.
Lines passing through white circles must pass straight through its cell, and make a right-angled turn in the cell next to the white circle (left or right).
Lines passing through black circles must make a right-angled turn in its cell, then it must go straight through the next cell (till the middle of the second cell) on both sides.

1. At 11:32 AM on 13 Jun 2007,

Hahaha! What an ace prediction I just made on the last topic...

2. At 11:42 AM on 13 Jun 2007,

I'm not sure I can make sense of those rules. If this is right:

Lines passing through white circles must pass straight through its cell, and make a right-angled turn in the cell next to the white circle (left or right).

Then the line of 3 white circles would appear to represent a contradiction because the squares to the left and right are also white circles. Oh, I get it! The "left or right" refers to the right angled turn - yes?

3. At 12:06 PM on 13 Jun 2007,

The rules are better explained on Wikipedia.

I still can't do it mind!

4. At 12:12 PM on 13 Jun 2007,

If I'm understandig the rules correctly then, your line must start or end in one of the pair of white circles at the bottom:

The line can't go straight through the two of them, because you're forced to turn on the square *after* a white circle, but not *on* a white circle.

So it must start on one or notionally go off the grid.
The rest baffles me though. 3rd attempt being rubbed out now...

5. At 12:20 PM on 13 Jun 2007,

SSC - if you use Wiki's rules, it can be done.

<Smug>I have done it</Smug>

Oh, and the solution is available here.

No peeking!

6. At 12:30 PM on 13 Jun 2007,

Lines passing through white circles must pass straight through its cell, and make a right-angled turn in the cell next to the white circle (left or right).

This is not clear - perhaps better written as:

"The line must pass straight though a cell with a white circle, but there must be a right angle turn in the cell before or after."

Hope this helps

7. At 12:32 PM on 13 Jun 2007,

Eddie: Are you still trying to solve this? I know you don't do Sudoku, and now you present us with this.

Well done, Stephen! I think I'll have to print it off - the instructions alone are making my brain hurt!

8. At 12:33 PM on 13 Jun 2007,

Stephen (5),

What about the bottom 2 whites? Is SSC right about the invisible but necessary starting point?
xx
ed

9. At 12:36 PM on 13 Jun 2007,

What I find infuriating about Sudoku is that I have many many other things I should be doing with my time but, once I start one, I cannot put it down until I have either finished it (increasingly rare) or messed it up.

As for that blob puzzle thingy...doesn't grip me enough to want to do it, sorry.

10. At 12:36 PM on 13 Jun 2007,

Oh well done SLoSTROP! And thanks for the solution because I would have had to try to do it - but just cheated instead. The rules, whilst not significantly different on wikipedia, are accompanied by an example which sort of alters them, so I would advise anybody wanting a challenge to check them out.

11. At 12:41 PM on 13 Jun 2007,

Stephen (6),
So you have to rewrite the rules to do the puzzle?

Hmmmm
ed

12. At 12:55 PM on 13 Jun 2007,

Omigod - I got as far as the second line of your rules Eddie, and lost the will to live! Please don't make me think about any of these things.....

I know, my brain will atrophy if I don't take up this kind of thing. Problem is, I think it's too late. Did I say "ironical" somewhere earlier today? Sheesh :-(

13. At 12:56 PM on 13 Jun 2007,

This is obviously an example of an NP-Complete problem which are the most difficult problems in non-deterministic polynomial time, in the sense that they are the smallest subclass of NP that could conceivably remain outside of the class of deterministic polynomial-time problems. Maybe this is because a deterministic, polynomial-time solution to any NP-complete problem would also be a solution to every other problem in NP.

Don't you think?

14. At 12:56 PM on 13 Jun 2007,

C*rse you, Red Baron!!! okay, Red Baron-san

I don't need yet another fiendish attempt to mangle my mind even more than it is already!

15. At 12:58 PM on 13 Jun 2007,

Big Sister (7) - I wouldn't even try! Although I have seen the answer - which I will post tomorrow!

16. At 01:14 PM on 13 Jun 2007,

AndyC (13)

That you can come out with all the NP-Complete problem talk is bad enough. But I understand what you are talking about. That is worse!

Ed (8)

The two circles at the bottom are a good place to start:

Clearly, the line must be horizontal through both, or it will leave the grid. There must be a turn just before or just after each, so there must be one in each of the cells either side. Now move to the black circle bottom left...

17. At 01:23 PM on 13 Jun 2007,

Hi Eddie, we've seen the answer too, Stephen, Leader of STROP has posted it today :)

18. At 01:35 PM on 13 Jun 2007,

Andycroak (13): I never thought I would hear someone discussing NP completeness outside of academia. Unfair, I feel, to leave everyone intellectually mugged when you could have taught them some advanced stuff...

For the uninitiated (i.e. those of you fortunate never to have studied theoretical computer science), think of a travelling salesman who has to visit a number of towns all linked by a number of different roads. You have to find the optimum (be it fastest or shortest distance) journey that allows him to visit every town. For a very small number of towns and roads this is a fairly simple proposition.

But as the number of towns and roads grows, the number of possible routes grows exponentially and you would run out of time trying to explore all possible routes to find out which is the optimum.

And all that without the sniff of a sale and no HP sauce to go on the bacon bap in the layby of the A6.

Watch this space for an explanation of Big O notation and Turing machines.....

19. At 01:37 PM on 13 Jun 2007,

Erm .... pass
(I can't do Sudoko either!)
I am beginning to feel an utter failure, but I am consoled by my cross stitcvh.

20. At 01:40 PM on 13 Jun 2007,

I played it and it was great.

21. At 01:58 PM on 13 Jun 2007,

AndyCHEAT!!! And I was so impressed!

22. At 02:17 PM on 13 Jun 2007,

Eddie - the good Lord didn't create anything without a purpose, but Sudoku comes close.

23. At 02:42 PM on 13 Jun 2007,

Andycroak (13) verbal diarrhoea can be very nasty. I have some excellent pills on the shelf.... ;-0)

24. At 02:52 PM on 13 Jun 2007,

hehe

http://news.bbc.co.uk/1/hi/england/hereford/worcs/6745977.stm

25. At 03:02 PM on 13 Jun 2007,

John H - how did you know I cheated?

Ok, I might be a computer whizz, but I found a link to NP-Completeness on wikipedia (from the Tin Cat's link) and just pasted all the bits I didn't understand. Sorry if you all thought I was about to launch a discussion on theoretical computer science :)

I just use computers to make things look pretty (see link above) ...

26. At 03:06 PM on 13 Jun 2007,

Aarghhh...I think my my last synapse just exploded - if that's what they do. And I spent yesterday lunch reading the Mornington Crescent rules on Wikipedia. I take it this thing is real though?

I look forward to the answer Eddie. Will it help in any way?

27. At 03:39 PM on 13 Jun 2007,

I have never successfully completed a sudoku in my life. Mind you, I've only ever tried about 4 times. My brain is just not wired in the right way.

I can though claim to have brought the thing to the PM's attention in March 2005:

(**wibbly-wobbly music to signify "going back in time"**)

Eric Muir (for it is he, reading a cue):

Why do you buy a newspaper? Is it for the in-depth coverage of politics? Or those important reports from foreign correspondents in dangerous places?

Perhaps the answer is a puzzle.

To be precise, a number puzzle called Sudoku (sue- doc - ooh).

It took off in Japan. Now Sudoku is promoted heavily in rival newspapers here.

Nigel Wrench has been poring over the the puzzle that's invading the correspondence pages of our most august newspapers...

[NAME: PUZZLE wrench pack
NUMBER: 10078
IN WORDS: sir, my husband
OUT WORDS: (a whisper) fantastic, done it
DURATION: 4'04'']

28. At 03:50 PM on 13 Jun 2007,

Do you have to wear a uniform of light blue shirt and beige trousers to joint Japan's Mathematical Association?

29. At 04:00 PM on 13 Jun 2007,

"IN WORDS: sir, my husband
OUT WORDS: (a whisper) fantastic, done it"

4 minutes and 4 seconds eh? :)

30. At 04:17 PM on 13 Jun 2007,

Tell Chris not to worry. It's not about genius in maths but specific spacial awareness. He does find some engaging stories doesn't he?

31. At 04:34 PM on 13 Jun 2007,

andycroak, have you been watching re-runs of The New Statesman?

32. At 04:44 PM on 13 Jun 2007,

I just knew this blog could not stay great forever.THat puzzle looks undoable. If at first you can't understand the instructions give up.

33. At 04:48 PM on 13 Jun 2007,

I started reading the rules to Maysu, then I remembered - I have a life.

34. At 04:50 PM on 13 Jun 2007,

The posted answer isn't the only one. Mine differs in at least two places.........

But that has been the case with Su-doku as well......

Surely the best puzzles only have one correct answer?

35. At 04:54 PM on 13 Jun 2007,

Glass box gone to room 404 again!

36. At 04:59 PM on 13 Jun 2007,

BlogPrince Marc: Ah, but some of us had already been doing them since the previous November ..... It all began in such a quiet way, but, like Topsy, it just grew and grew!

Like some other things I could mention, it's a great time waster, but the emphasis (as indeed for activities!) is on the great.

I have read that, like crosswords, sudoku is an excellent activity for keeping the synapses in good shape. So, question: Why if I can do sudoku do I keep forgetting things?

[Probable answer: Because I spend too long on the Blog.]

37. At 05:04 PM on 13 Jun 2007,

for those of you who are Dr Who fans there's a pictorial sudoku puzzle on the BBC Dr Who website which is quite fun especially if you're more at home with pictures than numbers.

38. At 05:28 PM on 13 Jun 2007,

hanjie is better. just fill in the squares and you end up with a picture.

39. At 05:34 PM on 13 Jun 2007,

hanjie is better. just fill in the squares and you end up with a picture.

40. At 05:51 PM on 13 Jun 2007,

I'm a bid sudoku'er (if there is such a phrase) but I too one look at the instructions to the puzzle here and thought "No Way!". It it takes that long to explain it, I don't think it's worth it, to be honest...

41. At 06:29 PM on 13 Jun 2007,

Insomniac correspondent checking in from the other side of the world .. sorry to hear that the instructions disappointed so many of you .. but then again if it made it a little harder that's no bad thing I guess ..

If you are really stuck there's a proper example of how to do it elsewhere on the BBC News website at http://news.bbc.co.uk/2/hi/asia-pacific/6745433.stm

You can try slitherlink - the game I mentioned in the package on the Nikoli website at http://www.nikoli.co.jp/en/puzzles/slitherlink/

Enjoy ..

42. At 06:54 PM on 13 Jun 2007,

I think White is winning. But I'm not that good at draughts.

43. At 08:03 PM on 13 Jun 2007,

Fearless (40) - are you by any chance using Admin Annie's new keyboard in your last post?

Andycrboffin - very impressive :o)

Frances 0 - you do make me smile!

... and no, I still haven't read the instructions - I know they wouldn't help. I'll stick to crosswords thanks.

44. At 09:19 PM on 13 Jun 2007,

Joanna - Hanjie is not better. Once you can do the most basic one, even the hardest is no harder, just longer!

45. At 11:31 PM on 13 Jun 2007,

Val, it certainly looks like Fearless has been using my keyboard - but how much longer can I go on blaming my bad typing on my new machine. Probably not much longer.
BTW I noticed your ironical on another thread, but kindly refrained from commenting - didn't want to bring a blush of shame to your girlish cheeks.

46. At 01:05 AM on 14 Jun 2007,

I've made an Excel-based helper for Sudoku...it's completely macro-free, and just automates the process of scribbling down which numbers could be valid for each cell, based on the numbers you've already entered. Please not that there's not much validation, so it isn't immune from GIGO.

If you're interested, it's on my pitiful excuse for a website (Geocities UK) - you should be able to work out my username from this post, and the file's linked to from somewhere on the homepage. There's also one for the 16x16 variation (with even less validation).

47. At 10:32 AM on 14 Jun 2007,

So Chris Hogg failed A-level maths. No hope for me, then. I didn't even take it (in the days before coursework). Freecell wastes enough time, anyway. On my Windoze 95 machine there are 32,000 combinations. Latest machine offers 1 million. That should see me out...

48. At 12:34 PM on 14 Jun 2007,

"At 05:28 PM on 13 Jun 2007, Joanna wrote:

hanjie is better. just fill in the squares and you end up with a picture."

Hi, Joanna! Hanjie is my favourite too. I'm now into the giant puzzles. They have advantage of using bits of brain that are available when listening to the radio.

49. At 07:11 PM on 14 Jun 2007,

mittfh (46) I've been using a helper which works in exactly the way you describe, but I call mine a pencil ;o)

50. At 09:20 PM on 17 Jun 2007,

Mittfh, this may sound odd, but it's a serious question: Do you have a brother called Gary?

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