Hard puzzle from sudoku.com. Do i need chains for this?

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Hard puzzle from sudoku.com. Do i need chains for this?

Postby Minethlos » Sun Jan 12, 2020 11:26 pm

Started solving and got stuck. Seems like the simple methods don't work anymore. Do I need chains? (I haven't used them yet.)
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Minethlos
 
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Re: Hard puzzle from sudoku.com. Do i need chains for this?

Postby speter » Wed Jan 15, 2020 4:06 am

There is a skyscraper...

Look at the candidate 1's in row 3:
+ if r3c3=1 then r7c3<>1 and r9c1=1
+ if r3c5=1 then r9c5<>1 and r9c1=1

cheers S
:)
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Re: Hard puzzle from sudoku.com. Do i need chains for this?

Postby docjohn » Tue Feb 18, 2020 5:17 pm

Skyscraper works well here (which is also an X-chain)
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