Thirith
Registered User regular

As an occasional Sudoku player and auto-didact, I find that with the difficult ones I often get to a point where I simply don't know how to proceed. I know various tricks how to get as far as possible, but at this point I'm usually reduced to making an educated guess.

Which is why I was wondering if there might be a Sudoku sensei here that could help me get the black belt. Take for instance the Sudoku here:

How do I proceed from this?

Which is why I was wondering if there might be a Sudoku sensei here that could help me get the black belt. Take for instance the Sudoku here:

How do I proceed from this?

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## Posts

Now how do you pick which one to guess on? I try and complete rows and squares. That vertical row with 237 has only 3 blank spaces. The upper right and far right squares are only missing two spaces each.

Also, I try to break it down by number. Fill in all the 1s then the 2s then the 3s etc. get stuck, move on to next number.

knitdanon-Indiana Solo, runner of blades

I cheated and punched it into an online solver and based on the numbers you have solved it said that there is a unique solution but there is no logical way to solve it within the limits of the program, so it essentially solved and checked it using guesses. There was the caveat that just because the program couldn't solve it logically didn't mean there wasn't a logical solution, but I take that to mean you have to hold so many numbers in your head at once with a ton of "if/and" type logic statements that you eventually get to a point where you're just guessing on the 4 & 6 in the top right or 2 & 8 on the mid right sections then running all the possibilities in your head to check them. Not a lot of help, but I stared at it for probably 10 minutes and ran out of all my usual tricks for solving these using logic.

Write 1-9 in all empty squares, then strike out the numbers that can't go in that square, and work from there.

And related, two Sudoku-like games I enjoy are 0hh1 and 0hn0.

"Nothing is gonna save us forever but a lot of things can save us today." - Night in the Woods

"Nothing is gonna save us forever but a lot of things can save us today." - Night in the Woods

-Indiana Solo, runner of blades

whythey work."Nothing is gonna save us forever but a lot of things can save us today." - Night in the Woods

garroad_ranonIn particular for the posted puzzle:

"Nothing is gonna save us forever but a lot of things can save us today." - Night in the Woods

Here's one way to progress:

Assume that R9C7 is not 9.

- The only other place for a 9 in Row 9 is R9C2, so that must be 9.

- Since R9C7 is not 9, R9C7 and R7C7 form a twin pair (5/8).

- That means R4C7 is not 8, so it must be 9.

- R5C9 is in the same Block as R4C7 and can no longer be 9, so it's 8.

- Row 5 now has only one place for a 9, in R5C2, so that must be 9.

- We've determined that R5C2 and R9C2 are both 9s, but they're both in column 2 which is a contradiction.

Our assumption that R9C7 is not 9 is therefore false, so it is 9.

It follows that R4C7 is 8 and R5C9 is 9, which eliminates 9 as a possibility in R5C2. R9C7 eliminates 9 as a possibility in R9C2, which leaves R5C2 and R9C2 as a 2/5 twin pair which eliminates a fair number of possibilities.

Guessing right is the worst. You want to fail asap, so if you can spot a square that has very few possibilities; rather than test from those spaces, test from spaces that rule those out. It also helps if you just do a pass considering only thr trial number. The above is a good example of 9s breaking nines; I went for 3's.

Why? That's really the question here, right?

Because there's very few options for three in Top Right, Top Center, Bottom Right, Bottom Center. And those also make a nice square, which is a perfect storm. Since each corner affects the other two (particularly so in this specific case), each guess has an immediate impact vertically and horizontally so it's quick to visualize/trial.

In my check, a 3 in the wrong spot in TR,TC,BC eliminated all possibilities in BR.

When I do these on paper, I just go number by numbers. All the 1s I can spot, 2s, etc, and I note how many of each I've found in the form of noting the missing numbers outside the square; sorry center square. So when I get stuck, I can start on the most guessable. 3-5 is usually fertile ground. Less than that and you're usually better off testing other numbers that impact their candidates, because they're probably either deadlocked or diagonal. More than that and you're probably still pretty wide open.

(But I'd be lying if I said any of that logic ever stopped me from wasting 30 minutes trying to dead reckon a puzzle with plenty of deterministic gimmes unfilled)

ArbitraryDescriptoron"Nothing is gonna save us forever but a lot of things can save us today." - Night in the Woods