| View previous topic :: View next topic |
| Author |
Message |
jez
Joined: 26 Feb 2006
Posts: 2
|
 Posted: Sun Feb 26, 2006 6:13 pm Post subject: Stumped on a 'hard' puzzle |
 |
|
Hi everyone, I'm rather stumped on a 'hard' puzzle from The Daily Sudoku a while back. Here's a screenie of where I got to and what TDS's script suggested next:
http://www.game-point.net/misc/sudoku.png
The red number is the suggestion. Now I can't for the life of me figure out why 9 has to go there. Seems that 9s can go in r3c4 and/or r1c9. Why does 9 have to go here? |
|
| Back to top |
|
 |
TKiel
Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI
|
| Posted: Sun Feb 26, 2006 6:57 pm Post subject: |
|
|
Jez,
After placing all the solved cells shown in the screenie, my candidate grid looked like this
| Code: |
*--------------------------------------------------------------------*
| 256 7 1 | 2569 25 4 | 3 8 59 |
| 3 2569 269 | 8 7 256 | 1 469 459 |
| 4 8 69 | 13569 135 356 | 69 7 2 |
|----------------------+----------------------+----------------------|
| 1 2569 269 | 235 8 235 | 4 39 7 |
| 8 3 7 | 4 9 1 | 2 5 6 |
| 25 259 4 | 235 6 7 | 8 39 1 |
|----------------------+----------------------+----------------------|
| 9 4 8 | 156 15 56 | 7 2 3 |
| 7 1 5 | 236 23 8 | 69 469 49 |
| 26 26 3 | 7 4 9 | 5 1 8 |
*--------------------------------------------------------------------*
|
which may or may not reflect your candidate list, depending on what exclusions you made between the time you solved for your last cell and created the image.
I don't see a way to directly place a 9 in the suggested cell from this position. A 9 does eventually go there, but there are some intermediate steps that need to be taken before that happens.
The candidate list shows a naked pair in column 8 and a naked triple in row 8. Once those exclusions are mad there is a naked triple in column 4, which leads to a naked triple in row 3. Then a naked pair in box 2 is revealed, which leads to the reduction of the candidates in r2c6 to only a 6, which, when placed, leaves 9 as the only candidate in r1c4, which solves the puzzle to where only single placements are needed to the end. |
|
| Back to top |
|
|
David Bryant
Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
|
| Posted: Sun Feb 26, 2006 7:17 pm Post subject: Why so complicated? |
|
|
| Code: | *--------------------------------------------------------------------*
| 256 7 1 | 2569 25 4 | 3 8 59 |
| 3 2569 269 | 8 7 256 | 1 469 459 |
| 4 8 69 | 13569 135 356 | 69 7 2 |
|----------------------+----------------------+----------------------|
| 1 2569 269 | 235 8 235 | 4 39 7 |
| 8 3 7 | 4 9 1 | 2 5 6 |
| 25 259 4 | 235 6 7 | 8 39 1 |
|----------------------+----------------------+----------------------|
| 9 4 8 | 156 15 56 | 7 2 3 |
| 7 1 5 | 236 23 8 | 69 469 49 |
| 26 26 3 | 7 4 9 | 5 1 8 |
*--------------------------------------------------------------------* |
There's a naked pair {6, 9} in row 3, at r3c3 & r3c7.
After eliminating {6, 9} in r3c4, r3c5 & r3c6 we see that the "9" at r1c4 is unique in the top center 3x3 box, that "2" is the sole candidate for r1c5, and that the "6" at r2c6 is also unique in the top center 3x3 box. dcb |
|
| Back to top |
|
|
Guest
|
| Posted: Sun Feb 26, 2006 7:19 pm Post subject: |
|
|
| TKiel wrote: | | The candidate list shows a naked pair in column 8 and a naked triple in row 8. Once those exclusions are mad there is a naked triple in column 4, which leads to a naked triple in row 3. Then a naked pair in box 2 is revealed, which leads to the reduction of the candidates in r2c6 to only a 6 |
Actually, I think you missed out that before that, you have to put a 2 in r1c5 (correct me if i'm wrong?), but thanks. Still, it leaves the question as to why TDS's hint machine gave me the 9 for the original problem. I wonder if you can directly place that number somehow. |
|
| Back to top |
|
|
TKiel
Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI
|
| Posted: Sun Feb 26, 2006 10:01 pm Post subject: |
|
|
You are correct. After making the exclusions from the naked pair in box 2, r1c5 has only 2 as a possibility. Once played, that leaves r2c6 with only 6 and when that is played, then r1c4 has only 9.
David's post above explains how the 9 can be directly placed in r1c4, without need to do all the stuff I outlined, which I totally missed. I've always found hidden pairs are usually harder to spot than even naked quads. |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
