The New Sudoku Players' Forum

[Sullydom]

I have never been completely stuck before, but I have hit the preverbial brickwall, on a puzzle given to me by someone who got caught at the same point, I believe it to be from the Sunday Times. The Pappacom Suduko program grades it as very hard. I have completed it through trial and error, but there must be a logical step, I just can't see it. I would be very grateful if someone could point me in the right direction.

3*****5*2
*247**869
*****23*4
6***4*728
482967153
73*28*496
**35**687
*17**6945
**6*7*231

Thanks in anticipation

[PaulIQ164]

Look at where the 4, 8 and 9 can and can't go in column 6. It should tell you something about where the 1 is in row 7.

[Sullydom]

I'm sorry, I have probably stared at this puzzle too long, I can't see your logic.

In row 7 1 can only go in square 5 or 6, but I can't see how you can rule out 1 in square 6

[PaulIQ164]

In column 6, you'll find that there are three cells that can't be 4, 8 or 9. Since there are only six gaps in column 6, that only leaves three places for the 4 8 and 9 to go. Three cells in three spaces means none of them can be anything but 4, 8 or 9. Specifically, there can't be a one in cell you mention.

[Kanfield]

Sullydom - you were not alone! I was stuck in exactly the same spot having congratulated myself on getting the x-wing on the 6's. The next step is comparatively straight forward yet for the life of me I could not see it. Perhaps you subconsciously relax after doing the hard bit and therefore miss the obvious?! Can anyone explain this phenomenon?

[PaulIQ164]

Look in column six. There are six unfilled cells in that column. The two in the central box cannot be 4 or 8 or 9, since those numbers already appear in the box. Similarly, the second cell down the column can't be 4 or 8 or 9, since all those numbers already appear in its row. So, out of the six cells still unfilled in the column, we have found three of them, none of which can be a 4 or an 8 or a 9. If those three can't hold the 4, 8 and 9, then the other three must (since the 4, 8 and 9 have to go somewhere in the column). One of these other three cells the cell at column 6, row 6. You have this cell as a possible place for the 1 to go in row 6. But we've just discovered that this cell has to be 4, 6 or 9. So it cannot be the 1.

[emm]

Perhaps you subconsciously relax after doing the hard bit and therefore miss the obvious?! Can anyone explain this phenomenon?

It's called the 'Ramp Aftereffect' and demonstrates the existence of selective transient visual pathways ie after you've hit the ramp and sailed across the void you then forget to concentrate on the obstacle at the other end!

[tentonipete]

funny. my sudoku partner in crime and i got stuck at exactly the same point.

am i right in thinking that the {1,3,5}{1,3,5}{1,5} is a naked triple?

just coming to terms with the terminology over here.

as for the bit leading up to this point being more difficult, we managed to reach the same place without using (knowingly) any xwings so it does not really feel like missing easy points after a difficult approach.

[Lardarse]

Yes, {135}{135}{15} is a naked triple, as is {24}{47}{27}

[squareman]

An alternative approach is to examine the location of the 4, 6 and 8 in the top centre box. These have to be in the three open corners. This allows you to complete the 1 in column 4.