The Sept 28 killer is actually a "Killer X" (i.e. no repetition on the 2 main diagonals). So with that in mind you could get a unique solution.

To all:

Regarding the Sept 27 killer, I've worked it out by hand and found it does have 1 unique solution only, though I shamelessly applied T&E more than a few times... (Is it really shameful to try T&E on that puzzle?)

That said, I think it's a perfectly valid puzzle, and when Mr. Tetsuya Nishio claimed that he could make a killer sudoku that a champion needs 6 hours to solve, this one strikes pretty close on that line (of course it's computer generated...) Surely a very tough challenge for everybody to sharpen their Killer solving techniques (one of the contradiction branch goes all the way to fill almost the whole grid and only fails on one single cage...)

Paul, I think you made a mistake there. 5+1+2+3+7 actually leads to the correct solution, and 5+1+2+4+6 instead leads to a contradiction eventually, but I could fill box 5 and go a long way before that happens. In fact the contradiction that almost had the whole grid filled is actually one of the branches from there. To show you, consider the following configuration of rows 4-6:PaulIQ164 wrote:I got those 3 cells, but it was trial&error really (though I doubt the boundaries are as clear in Killers as the already fuzzy sudoku ones). The 5 in row 4 has to be in the 18-cage, and there's only two ways to make 18 in 5 cells using a 5 (5+1+2+4+6; 5+1+2+3+7). The latter leads to an impossibility when you try to fill box5, so it must be the first alternative, which lets you fill the box correctly.

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`{123} {123} {23} {8} {7} {4} {9} {56} {56}`

{678} {678} {678} {9} {3} {5} {24} {124} {124}

{45} {45} {9} {2} {6} {1} {378} {378} {378}