SudoCue Users Forum Index SudoCue Users
A forum for users of the SudoCue programs and the services of SudoCue.Net
 
 FAQFAQ   SearchSearch   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Daily Nightmare 2-5-07

 
Post new topic   Reply to topic    SudoCue Users Forum Index -> Daily Sudoku Nightmare & Archive
View previous topic :: View next topic  
Author Message
CathyW
Master
Master


Joined: 31 Jan 2007
Posts: 161
Location: Hertfordshire, UK

PostPosted: Wed May 02, 2007 10:59 am    Post subject: Daily Nightmare 2-5-07 Reply with quote

Don't look if you haven't done today's puzzle yet!!






I found a cool uniqueness move, an x-wing and finally a forcing chain to solve this puzzle Very Happy

My walkthrough:

1. NP {28} in N5 -> r4c4=6 -> NP {39} in c6/N5 -> r1c6 = 1/6/7
2. NT {147} in c6/N8 -> r1c6 = 6, r9c4 = 2/5/8
3. NP {57} in c4/N2 -> r1c4 = 1, r23c5 = {39}, r9c4 = 2/8
4. HS r6c6 = 3, r4c6 = 9

5. Grid now:
Code:
 
 *-----------------------------------------------------------------------------*
 | 2       379     3579    | 1       4       6       | 35      79      8       |
 | 457     3479    1       | 57      39      8       | 2       4679    4569    |
 | 4578    6       345789  | 57      39      2       | 345     1       459     |
 |-------------------------+-------------------------+-------------------------|
 | 48      234     348     | 6       1       9       | 7       5       249     |
 | 9       127     78      | 4       28      5       | 168     268     3       |
 | 148     5       6       | 28      7       3       | 148     2489    1249    |
 |-------------------------+-------------------------+-------------------------|
 | 14567   8       457     | 9       25      147     | 1456    3       12456   |
 | 14567   147     2       | 3       58      147     | 9       468     1456    |
 | 3       149     459     | 28      6       14      | 1458    248     7       |
 *-----------------------------------------------------------------------------*

r23c4 = {57} -> r23c1 cannot both be {57}
Either r2c1 = 4 or r3c1 = 4 or 8.
Since r4c1 = 4/8, 4 and 8 cannot go elsewhere in c1 -> r6c1 = 1 -> r78c1 = {567}
6. NT {278} in r5c235 -> r5c8 = 6, r5c7 = 1
7. 8 locked to r6 in N6 -> r6c4 = 2 -> several naked and hidden singles to here:

Code:

 *--------------------------------------------------------------------*
 | 2      379    359    | 1      4      6      | 35     79     8      |
 | 457    3479   1      | 57     39     8      | 2      479    6      |
 | 4578   6      34589  | 57     39     2      | 345    1      459    |
 |----------------------+----------------------+----------------------|
 | 48     34     348    | 6      1      9      | 7      5      2      |
 | 9      2      7      | 4      8      5      | 1      6      3      |
 | 1      5      6      | 2      7      3      | 8      49     49     |
 |----------------------+----------------------+----------------------|
 | 57     8      45     | 9      2      147    | 6      3      145    |
 | 6      147    2      | 3      5      147    | 9      8      14     |
 | 3      149    459    | 8      6      14     | 45     2      7      |
 *--------------------------------------------------------------------*

8. x-wing on 5 in r1c37, r9c37 -> r3c3, r3c7, r7c3 <> 5 -> r7c3 = 4
9. Forcing chain:
If r7c6 = 1 -> r9c6 = 4, r9c7 = 5, r9c3 = 9, r9c2 = 1, r8c2 = 7
If r7c6 = 7 -> r7c1 = 5, r9c3 = 9, r9c2 = 1, r8c2 = 7
The rest is singles.
Back to top
View user's profile Send private message
Para
Yokozuna
Yokozuna


Joined: 08 Nov 2006
Posts: 384
Location: The Netherlands

PostPosted: Wed May 02, 2007 12:07 pm    Post subject: Re: Daily Nightmare 2-5-07 Reply with quote

Hi

I missed that UR and went through an alternative solution path. Tend to miss unique subset moves.
But for your walkthrough, that forcing chain can be replaced by: xy-wing: On R7C19 + R8C2: R8C9 <> 1

greetings

Para
Back to top
View user's profile Send private message
CathyW
Master
Master


Joined: 31 Jan 2007
Posts: 161
Location: Hertfordshire, UK

PostPosted: Wed May 02, 2007 12:56 pm    Post subject: Reply with quote

So it can! Thanks - should have spotted that. Rolling Eyes

I was pleased with the UR move - I can't remember using UR in combination with a bivalue cell before to make eliminations. I know some people don't hold with using uniqueness moves but I find them valuable and I'm 100% certain that Ruud would not supply a puzzle with more than one solution. Smile
Back to top
View user's profile Send private message
rep'nA
Hooked
Hooked


Joined: 19 Jan 2007
Posts: 49
Location: Union City, California

PostPosted: Wed May 02, 2007 11:58 pm    Post subject: Re: Daily Nightmare 2-5-07 Reply with quote

Or at this point...

Code:

 *--------------------------------------------------------------------*
 | 2      379    359    | 1      4      6      | 35     79     8      |
 | 457    3479   1      | 57     39     8      | 2      479    6      |
 | 4578   6      34589  | 57     39     2      | 345    1      459    |
 |----------------------+----------------------+----------------------|
 | 48     34     348    | 6      1      9      | 7      5      2      |
 | 9      2      7      | 4      8      5      | 1      6      3      |
 | 1      5      6      | 2      7      3      | 8      49     49     |
 |----------------------+----------------------+----------------------|
 | 57     8      45     | 9      2      147    | 6      3      145    |
 | 6      147    2      | 3      5      147    | 9      8      14     |
 | 3      149    459    | 8      6      14     | 45     2      7      |
 *--------------------------------------------------------------------*


you could skip both the x-wing and the forcing chain (or Para's alternative) with Subset Counting on r7c136 and r9c67 (or equivalently the ALS xz-rule). The candidates 1,4,5,7 appear with max multiplicities {1,2,2,1}. As there are 5 cells, any placement eliminating all of the 4's or all of the 5's must be false. Hence, r7c9, r9c3 <> 5, and the puzzle is reduced to singles.
_________________
"Obviousness is always the enemy to correctness."-Bertrand Russell
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    SudoCue Users Forum Index -> Daily Sudoku Nightmare & Archive All times are GMT
Page 1 of 1

 
Jump to:  
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