Stuck with a Sudoku

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Stuck with a Sudoku

Postby Scott_be » Tue 27 Oct, 2015 4:24 pm

Can anyone help with this sudoku please? I'm stuck at this point. I tried solver websites. They do find one unique solution, but can't tell which next logic step leads to solving the puzzle. The last step I was able to make was an XYZ elimination of a 2 in the indicated cell. Can anyone help me finding that one next logic step please? Best regards, Scott.
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Re: Stuck with a Sudoku

Postby afcwarren » Tue 27 Oct, 2015 5:02 pm

Someone clever than me will no doubt come up with better logic but the 2s form a chain. If the cell in row 2 column 3 (R2C3) was a 2, then following this through to R6C3, R6C7 and then R2C8, there would be two 2s in row 2 - therefore R2C3 cannot be a 2.
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Re: Stuck with a Sudoku

Postby detuned » Wed 28 Oct, 2015 11:28 pm

R3C7 is a 3 - see what happens when you try a 2 or a 4 there.

To see what is really going on, try and see what's going on with the pairs in column 2 and row 6 - this is an example of a technique known as "colouring". It's quite nice that you can do this with two numbers (i.e. 2's and 4's) on this occasion!
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Re: Stuck with a Sudoku

Postby Scott_be » Thu 29 Oct, 2015 6:14 am

Thank you for your help afcwarren and detuned! Much appreciated. This solved the puzzle :) thank you
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Re: Stuck with a Sudoku

Postby Fred76 » Fri 30 Oct, 2015 12:01 am

I'll add my 2 cents here.

The 1rst trick I saw on this one was to use uniqueness technique on the 3 bottom regions. You have to place the 8 in R9C8, otherwise you'll have a big loop with digits 2, 4, 6 and 9 (in columns 1, 2, 6, 8) that would have 2 solutions.

But colouring is fine, too, of course ;)

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