The New Sudoku Players' Forum

[mnmid]

Ok, I'm new to these puzzles. Occasionally, I come upon a puzzle where I get stuck and can not determine any box by logic. I have always been able
to procede and solve the puzzle by guessing one box as I did this one. Are there puzzles that require guessing? If not, what is the next move in the following puzzle and what logic dictates it? This puzzle appeared in the Madison WI State Journal on 7/20/05.

7 ? ? 1 ? 8 ? 2 6
1 ? ? ? ? 9 7 ? ?
8 ? 6 7 ? ? 1 9 ?
3 8 2 ? 7 5 ? 1 9 the first ? is a 6 by guessing
4 6 5 2 9 1 ? 7 ?
9 7 1 8 ? ? 2 ? 5
2 4 7 9 8 6 ? ? 1
6 ? ? 5 1 2 ? ? 7
5 1 ? 3 4 7 ? ? 2

Thanks, Mike Dorl

[PaulIQ164]

If you look at the rightmost column, the 4 has to be in one of the top two cells, the ones in the top-right box. This means the 4 in the top-right box can't be in any of the other cells in that box. Knowing that, there's now only one place the 4 can be in the topmost row.

All good sudoku puzzles can be solved without guessing. Not to sound too sycophantic, but all Pappocom ones are like this.

Also, this post should really have been in the "General/puzzle" forum.

[miroz]

7,9,4,1,5,8,3,2,6
1,2,3,4,6,9,7,5,8
8,5,6,7,2,3,1,9,4
3,8,2,6,7,5,4,1,9
4,6,5,2,9,1,8,7,3
9,7,1,8,3,4,2,6,5
2,4,7,9,8,6,5,3,1
6,3,8,5,1,2,9,4,7
5,1,9,3,4,7,6,8,2

[Cec]

PaulIQ164 wrote in reply to mnmid "If you look at the right most column, the 4 has to be in one of the top two cells, the ones in the top right box. This means the 4 in the top right box can't be in any of the other cells in that box. Knowing that, there's now only one place the 4 can be in the topmost row"

No offence PaulIQ164 but suggest you use Pappocom's "Basic terms" posted 5th March which suggests we all use the same terms.

I can't follow your reference to the 4 having "to be in one of the top two cells, the ones in the top right box". On my reckoning, there are four vacant cells in row 1, with Box 3 containing one of these in this row (ie column 7)

I welcome your reply using Pappocom's recommended terms, in particular by referring to cells such as r1c7 for the cell mentioned in Box 3 above.

Regards Bonsai Cec

[PaulIQ164]

Well I believe I did use the standard terms, but if it's hard to follow like that, what I meant was:

In column 9, there are only two cells that the 4 can go in: r2c9 and r3c9. Both of these are in box 3, so the 4 in box 3 cannot therefore go anywhere else (i.e., it cannot be in r1c7 or r2c8). This only leaves one possibility for the 4 in row 1.