The New Sudoku Players' Forum

[Rich]

*-----------*
|..2|6..|.5.|
|..1|...|.4.|
|64.|..8|..2|
|---+---+---|
|...|1.2|7..|
|.5.|.9.|.8.|
|..9|3.7|...|
|---+---+---|
|8..|2..|.95|
|.9.|...|3..|
|.2.|..5|8..|
*-----------*




*-----------------------------------------------------------*
| 379 378 2 | 6 34 349 | 1 5 378 |
| 3579 378 1 | 57 2 39 | 6 4 378 |
| 6 4 35 | 57 1 8 | 9 37 2 |
|-------------------+-------------------+-------------------|
| 4 36 8 | 1 5 2 | 7 36 9 |
| 13 5 7 | 4 9 6 | 2 8 13 |
| 2 16 9 | 3 8 7 | 5 16 4 |
|-------------------+-------------------+-------------------|
| 8 137 36 | 2 367 13 | 4 9 5 |
| 157 9 456 | 8 467 14 | 3 2 67 |
| 37 2 346 | 9 3467 5 | 8 17 167 |
*-----------------------------------------------------------*

This is an expert puzzle from simple sudoku. I finally gave up and asked for a hint. The hint was to eliminate the 3 from r1c2 based on coloring. I thought I understood coloring or at least the basics of coloring, but I don't understand the logic of this. It seems like you could also eliminate the 3 from r2c2. Where am I going wrong?
Thanks,
Rich

[ravel]

Either r3c3=3 or (r3c8=3,r4c8<>3) r4c2=3. So you can eliminate 3 from the cells, which "see" both: r123c3.
Please mark your puzzle and candidates and click on the code button to keep it formatted.

[Sped]

Code: Select all

 *-----------------------------------------------------------*
 | 379   378   2     | 6     34    349   | 1     5     378   |
 | 3579  378   1     | 57    2     39    | 6     4     378   |
 | 6     4     35    | 57    1     8     | 9     37    2     |
 |-------------------+-------------------+-------------------|
 | 4     36    8     | 1     5     2     | 7     36    9     |
 | 13    5     7     | 4     9     6     | 2     8     13    |
 | 2     16    9     | 3     8     7     | 5     16    4     |
 |-------------------+-------------------+-------------------|
 | 8     137   36    | 2     367   13    | 4     9     5     |
 | 157   9     456   | 8     467   14    | 3     2     67    |
 | 37    2     346   | 9     3467  5     | 8     17    167   |
 *-----------------------------------------------------------*


Filter on threes. There are 2 candidates in box 4. They form a conjugate pair. i.e. one must be 3 and the other not. Color r5c1 blue, and r4c2 green.

Likewise there is a conjugate pair in row 4. r4c2 is green so color r4c8 blue.

There is a conjugate pair in column 8. r4c8 is already blue, so color r3c8 green.

There is a conjugate pair in row 3. r3c8 is already green so color r3c3 blue.

You'll notice in box 1 that r1c2, r2c2, and r3c2 share a group with both r4c2 (same column), which is green, and r3c3 (same box), which is blue.

Either the blues or greens are 3s. We don't know which, but it's one or the other. It doesn't matter though, because those 3 cells in box 1 share a group with both blue and green. Therefore 3s can be eliminated from column 2 in box 1.

[Cec]

Likewise there is a conjugate pair in row 4. r4c2 is green so color r4c7 blue.

There is a conjugate pair in column 7. r4c7 is already blue, so color r3c7 green.

There is a conjugate pair in row 3. r3c7 is already green so color r3c3 blue..."

Hi Sped,

You say r4c2 is green (that's OK) but don't you then mean "so color r4c8" rather than r4c7?
You also say "r4c7 is already blue". No, because this cell already has a 7 placed there. I haven't checked the rest of it - I thought I'd let you do it.
Apart from these typos I like your clear explanation on coloring.
Cec

[Sped]

Hi Sped,

You say r4c2 is green (that's OK) but don't you then mean "so color r4c8" rather than r4c7?
You also say "r4c7 is already blue". No, because this cell already has a 7 placed there. I haven't checked the rest of it - I thought I'd let you do it.
Apart from these typos I like your clear explanation on coloring.
Cec

You're right.. Somehow I got columns 7 and 8 confused. Aside from that, I think the explanation holds up. Thanks for the correction.

I've edited the original message.

[ronk]

Thanks for the correction. Let's try again:

I think most people would edit their original post.

[Sped]

I think most people would edit their original post.

You can edit messages?

I'll try it. Thanks fior the tip.