Killer Sudoku - I need help

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Killer Sudoku - I need help

Postby ole1975 » Fri Jun 26, 2020 9:20 am

I love solving difficult sudoku / killer sudoku. I consider myself skilled - but now I need help to solve this puzzle.

I've been trying for over 2 hours, I can't find a start. See attachment.
I'm not interested in the solution, just a start strategy.

This puzzle is from Killer Sudoku app (iPhone) - build by Sarah Pierce
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Re: Killer Sudoku - I need help

Postby Mathimagics » Sat Jun 27, 2020 1:47 pm

I'd look at the bi-value {5,7} in r3c2. Note that box 4 contains a 2-cell sum 14 cage, and this means that cell r4c4 must be either 8 or 9.

If r3c2 = 7 then this forces r4c1 = 7, r4c23 = {95}, r4c4 = 8 and also fixes pairs in r3c56 and r3c78. It also forces r23c1 = {12} and this quickly leads to a contradiction wrt the 3-cell sum 17 cage in c1. We can conclude, then, that r3c2 = 5.

I know this T&E method will be anathema to some, but there you go! 8-)

PS: you have pencilmarks {234} in both r3c5 and r3c6. This is clearly wrong (4+3 leaves 19 to fill in r3c78).
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