The New Sudoku Players' Forum

[diavol]

I spent quite a lot of time on this one. I am a beginer sudoku player, but this one struck a nerve with me. I tried most of the methods I could find with no luck, I am probably missing something really silly to get this rolling again. Hopefully someone can point me in the right direction.

Code: Select all

 3 . 1 | 2 8 . | . . 7
 . . . | 1 . 7 | . . .
 7 . 6 | 9 3 4 | 5 1 .
-------+-------+-------
 . 7 . | 4 . 9 | 1 8 .
 9 . 8 | . 2 1 | 7 . 4
 . 1 . | 8 7 3 | . 5 .
-------+-------+-------
 . . 9 | . 4 . | 3 7 1
 . . . | 7 . 2 | 8 . 5
 . . 7 | 3 . 8 | . . 6


Any help would be appretiated.

[Shazbot]

without seeing your candidate list I can't tell how far you've got in excluding candidates.

If you've checked for naked pairs and eliminated based on all those, there's a naked triple of 4, 5, 9 in column 2 (rows 1, 2 and 9) allowing you to remove 5 as a candidate from column 2 row 5. That leaves only 1 place for the 5 in row 5. After that it should be smooth sailing.

If you can't see how I got to that point say so and I'll post from your grid with the candidate list.

[diavol]

without seeing your candidate list I can't tell how far you've got in excluding candidates.

If you've checked for naked pairs and eliminated based on all those, there's a naked triple of 4, 5, 9 in column 2 (rows 1, 2 and 9) allowing you to remove 5 as a candidate from column 2 row 5. That leaves only 1 place for the 5 in row 5. After that it should be smooth sailing.

If you can't see how I got to that point say so and I'll post from your grid with the candidate list.

Ok here is my candidate list:

Code: Select all

 3 459 1 | 2 8 56 | 469 469 7
 245 459 245 | 1 56 7 | 2469 23469 2389
 7 28 6 | 9 3 4 | 5 1 28
 256 7 235 | 4 56 9 | 1 8 23
 9 356 8 | 56 2 1 | 7 36 4
 246 1 24 | 8 7 3 | 269 5 29
 28 28 9 | 56 4 56 | 3 7 1
 146 346 34 | 7 19 2 | 8 49 5
 145 45 7 | 3 19 8 | 249 249 6

I don't see how you can get a naked triple out of 2nd column. And since this is a pappocom puzzle, I tried the 5 where you said it should be and that is not correct

[CathyW]

I agree with Shaz - you can remove the 5 from r5c2 (because of the (459) triple in column 2 - you have 459 in r1c2, r2c2 and 45 in r9c2), giving you a (36) pair in r5c2 and r5c8. Therefore the 5 has to go in r5c4, so not sure why Pappocom would indicate it can't go there The rest is fairly straightforward.

[Shazbot]

I'm not sure how you managed to eliminate 8 from r2c1 (if you've done that and it's correct, then r1c7=8, r3c2=8 and r2c9=8). Here's MY candidate list as close to yours as I can make it, and I'll explain from there.

Code: Select all

 *--------------------------------------------------------------------*
 | 3      459    1      | 2      8      56     | 469    469    7      |
 | 2458   24589  245    | 1      56     7      | 2469   23469  2389   |
 | 7      28     6      | 9      3      4      | 5      1      28     |
 |----------------------+----------------------+----------------------|
 | 256    7      235    | 4      56     9      | 1      8      23     |
 | 9      356    8      | 56     2      1      | 7      36     4      |
 | 246    1      24     | 8      7      3      | 269    5      29     |
 |----------------------+----------------------+----------------------|
 | 28     28     9      | 56     4      56     | 3      7      1      |
 | 146    346    34     | 7      19     2      | 8      49     5      |
 | 145    45     7      | 3      19     8      | 249    249    6      |
 *--------------------------------------------------------------------*


Naked pair (2,8) in column 2 allows you to exclude 2,8 from r2c2.

Then the three cells - r1c2, r2c2 and r9c2 contain only candidates 4,5 and 9 - there's the naked triple I referred to, allowing you to remove 4,5 and 9 as candidates from r5c2 and r8c2.

That leaves only one place for the 5 to go in row 5, and from there you have a few naked singles to fill in with the odd hidden single here and there, and should be able to complete the puzzle fairly easily.

As it happens, the 8 in row 2 DOES go in column 9, but I still can't see how you've done it. Perhaps you can explain how you were able to eliminate it from both r2c1 and r2c2?

[diavol]

Shazbot, my reasoning here is that
if r2c3 = 8 then r2c7 = 2
if r2c3 = 2 then r2c7 = 8,

so every other 28 can be eliminated from that row.

However, I don't see why r1c7 must be 8 because of that. I thank you guys for finding that naked 459 there, that helped me solve the puzzle in no time, can't believe I didn't see it before

[Shazbot]

Hi diavol,

I think you need to check your notation. You're talking about r2c3 and r2c7 - row 2, column 3 and row 2, column 7. 8 is not a candidate in either of those cells, and you could only eliminate 28 from the rest of the cells if you had a naked or hidden pair - I don't think there WAS a 28 pair anywhere there.

I think you may be getting the terms row and column confused - a row goes across, a column goes down, so if you're referring to the 28 in the first 3x3 block, you're actually looking at ROW 3, COLUMN 2, not r2c3.

However, there IS a 28 naked pair in r3c2 and r7c2, which would allow you to eliminate all other 2s and 8s from COLUMN 2, but that wouldn't allow you to eliminate the 8 from r2c1.

And going on from your question... you've somehow eliminated the 8 from r2c1, which leaves r3c2 as the only position for the 8 in box 1. That means (going by your own logic with the r/c swapped around) that r7c2 must be 2, leaving r7c1 as the only place in THAT box for the 8 to be. But I think you must have "fluked" the removal of 8 from r2c1 to get to that stage.