Stumped on this Sudoku

November 17, 2013 3:25 PM

I've been stuck on this Sudoku for weeks. What's the next step?

I've erased & restarted this puzzle enough that the ink's starting to come off the paper.

Here's all I know for sure.

Here's everything I've penciled in as possibilities this last time through.

I've read a number of different pages with Sudoku tips and strategies, and I'm just not seeing the next step here. Any idea what it is?

posted by johnofjack to Sports, Hobbies, & Recreation (14 answers total)

Why do you think the 3 (in the bottom row, middle square) goes there?
posted by travelwithcats at 3:32 PM on November 17, 2013

travelwithcats: the 3 has to go there because on the bottom right square, the 3 has to go on the bottom row, so that limits the 3 in the bottom middle to the top right.
posted by brainmouse at 3:35 PM on November 17, 2013

travelwithcats, there must be a 3 in the bottom row of the SE square, so that's the only place left for a 3 in the S square.
posted by Pre-Taped Call In Show at 3:35 PM on November 17, 2013

http://en.wikipedia.org/wiki/Backtracking

There exist many solvers, which you probably do not want. But the formal way to mechanically do a Sudoku is there.
posted by curuinor at 3:37 PM on November 17, 2013

Right, missed that. Thx.
posted by travelwithcats at 3:39 PM on November 17, 2013

In the northeast section, the middle-left square (I have no idea what the proper address system is, sorry), must be a 2.

Rationale: it can't be in the topmost row nor the bottommost row, it can't be in the middle column, and there's a 7 occupying the rightmost column.
posted by ceribus peribus at 3:39 PM on November 17, 2013

In the east section, the top-right square must be a 3
posted by pipeski at 3:40 PM on November 17, 2013

Oops. You had that. Then D6 and F6 are a 'pointing pair', so you can remove some possibilities in that column.
posted by pipeski at 3:45 PM on November 17, 2013

Best answer: I got stuck too, went to a sudoku solver, which suggests that this does not have a unique solution. (Click on solution count.)
posted by jeather at 3:52 PM on November 17, 2013 [2 favorites]

But actually, after removing a couple more candidates I don't think the puzzle is soluble without taking a guess. On preview,seconding jeather.
posted by pipeski at 3:52 PM on November 17, 2013

Best answer: Incidentally, that link points to a step-by-step solver, which is convenient if you only want the single next step and an explanation of why it is the next step, it doesn't solve the entire puzzle for you at once.
posted by jeather at 3:53 PM on November 17, 2013

Response by poster: That's very interesting, jeather. It never occurred to me that the puzzle might be faulty. I tried that link, going through the puzzle step by step, and when it got to where I was (filling in possibilities on a few cells I didn't bother with), all the strategies read "No" all the way down and it told me to check that there was only one solution. And it reports that it quit counting at 500 possible solutions.

This came from a book with 15 kinds of puzzles, and about 20 of each. Doesn't really inspire confidence for the rest of them. (Goodreads reminds me that I'd given up on the book altogether for about a year, stuck on this same puzzle.)
posted by johnofjack at 4:07 PM on November 17, 2013

Sorry to be late in. I also found that there was no unique solution. I am an avid sudoku solver and I use Simple Sudoku. You can use it to input problems and then solve them on the computer, or it can generate puzzles for you at a variety of levels. I really like it.
posted by mukade at 4:45 PM on November 17, 2013 [1 favorite]

That's not a valid Sudoku by the usual "only one possible solution" metric.

That puzzle has 6130 distinct solutions, no wonder you are having troubles!
posted by hardcode at 3:42 AM on November 19, 2013