Nishio sudoku strategy update#
Nishio sudoku strategy trial#
Nishio sudoku strategy series#

If you are unlucky, you will play through the tiring exercise of computer logic, trying path after path, sometimes going on and on until the final unit contradicts you. If you are “lucky”, you’ll hit on a quick contradiction, try the opposite, and mark the quick collapse. Followers of this blog realize how much Nishio covers up, replacing the challenge of decoding the logic of the puzzle with a mechanical search for a solution, as if it were the final solution that is important. I maintain that human solvers could double their Sudoku pleasure by just swearing off all Nishio methods, regardless of definition. Now imagine how limiting on the choice of Nishio candidates this requirement is. One can test for patterns of the remaining candidates by attempting a single freeform excluding the Nishio candidate and the candidates it sees. Our recent exploration of pattern enumeration tells us what is involved in imposing this limit.

Nishio sudoku strategy trial#

Other writers define Nishio as a limited form of trial and error in which the chosen candidate in the second step is assumed false if “it prevents the remaining placements of the candidate’s number”. Others require also a bifurcation in a Nishio. Outside of that, there is some confusion in the Sudoku community about the meaning of the term.įor some, Nishio is simply (1) choose any candidate, (2) take it to be true and (3) solve to a solution or a contradiction. Crediting the removal to a Nishio technique is to belittle the logical accomplishment here.Ī common theme of Nishio methods is the arbitrary selection of a candidate, and the determination of the consequences of it being true. I was elated to find an X-chain example of grouped pincers back in the post X-panel analysis. Would you do that? I trust that readers of this blog would construct the AIC from r7c2 to r8c9, then realize the extensions to the 6-groups, forming the effective toxic set. For his Nishio forcing chain, he selects the 6-candidate in r9c4 as the emanating candidate, perhaps because it eliminates the 6-group in SWr9, then seeks an AIC from the 6-group in Sr8 back to the first group. Stuart’s current sudowiki example of a Nishio forcing chain turns out to be an interesting ANL with grouped toxic set members. Here we also assert that techniques labeled “Nishio” in the Sudoku community, including this one, are contrary to sysudokie solving objectives.

Nishio sudoku strategy series#

There are puzzles at the highest difficulty that cannot be solved without guessing, and indeed some have more than one solution (depending on who made it and how diligently it was designed.Resuming the series on forcing chains, this post reveals that the Nishio forcing chain introduced on Andrew Stuart’s sudokuwiki site is yet another re-interpretation of the AIC toxic set, a.k.a. I did this with one hand on my phone because my 5-month-old refuses to not be held and walked around the house.

Using this as a starting point, I was able to logically fill out the rest of the puzzle: These 4 positions are coupled together, forcing an additional elimination. I don't have any other name for it, but the way I see it You can see here, regardless of whether you put 4 or an 8 in r2c1, r3c5 will be the other, which means (without guessing) you know r3c3 cannot be a 4.

You find couples of pointing pairs that are linked together in a set of 4, which regardless of which number is placed in it can also eliminate candidates. For those unaware of what 'pointing pairs' are (like I was, even though I used the method) here's a link to information on that.

Nishio sudoku strategy update#

So I'll update the rest of the answer from here to explain what I did in addition. Others have pointed out the correct start point but not linked it to a method.Īfter comment and further review I see that my method is just an extension of pointing pairs, which was already employed on the puzzle.