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First time I post a vh sudoku

 
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peter urhegyi



Joined: 26 Oct 2020
Posts: 27

PostPosted: Mon Nov 09, 2020 10:47 am    Post subject: First time I post a vh sudoku Reply with quote

Code:
..12..3..
.2...45..
4...5...2
6...4...1
..57..8..
.8...6..5
76..1...3
.......97
..23..18.
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peter urhegyi



Joined: 26 Oct 2020
Posts: 27

PostPosted: Mon Nov 09, 2020 11:21 am    Post subject: The pencilmarks grid from this 5-step VH sudoku Reply with quote

Code:
.-------------------.--------------------.------------------.
| 589   579   1     | 2     6789   789   | 3     467   4689 |
| 389   2     36789 | 1689  36789  4     | 5     167   689  |
| 4     379   36789 | 1689  5      13789 | 679   167   2    |
:-------------------+--------------------+------------------:
| 6     379   379   | 589   4      23589 | 279   237   1    |
| 1239  1349  5     | 7     239    1239  | 8     2346  469  |
| 1239  8     3479  | 19    239    6     | 2479  2347  5    |
:-------------------+--------------------+------------------:
| 7     6     489   | 4589  1      2589  | 24    245   3    |
| 1358  1345  348   | 4568  268    258   | 246   9     7    |
| 59    459   2     | 3     679    579   | 1     8     46   |
'-------------------'--------------------'------------------'
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Mon Nov 09, 2020 4:28 pm    Post subject: Reply with quote

Hello peter, hello all. Be forewarned, this one came up as EXTREME when I plugged it into my external program.


cheers...immp
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Mon Nov 09, 2020 5:12 pm    Post subject: Reply with quote

Lots of neat stuff in this one peter. Even spotted a swordfish (or two). Thanks for posting.

cheers...immp
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peter urhegyi



Joined: 26 Oct 2020
Posts: 27

PostPosted: Mon Nov 09, 2020 5:25 pm    Post subject: Reply with quote

immpy wrote:
Lots of neat stuff in this one peter. Even spotted a swordfish (or two). Thanks for posting.

cheers...immp

Thank you. After the discovery of the 2 swordfishes thisone needs only an x-wing , an xy-wing and an xyz-wing and a few basic steps like hidden and naked doubles and or triples.
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dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Mon Nov 09, 2020 6:55 pm    Post subject: Reply with quote

Wow! I had a tough time with this one! After basics:
Code:

+-----------------+-----------------+---------------+
| 589  579  1     | 2    6789  789  | 3    467 4689 |
| 389  2    36789 | 1689 36789 4    | 5    167 689  |
| 4    379  36789 | 1689 5     13   | 679  167 2    |
+-----------------+-----------------+---------------+
| 6    379  379   | 58   4     58   | 79   2   1    |
| 129  149  5     | 7    239   13   | 8    346 469  |
| 129  8    479   | 19   239   6    | 479  347 5    |
+-----------------+-----------------+---------------+
| 7    6    489   | 489  1     289  | 24   5   3    |
| 1358 1345 348   | 4568 68    258  | 246  9   7    |
| 59   459  2     | 3    679   579  | 1    8   46   |
+-----------------+-----------------+---------------+

4r9c9-[(4=5|9)r9c12-(59=7*)r9c6 -(4=2*)r7c7]-(24=6)r8c7-(6=8)r8c5-(2*8=9)r7c6-(7*9=8)r1c6-r3c4=r3c3-r78c3=r8c1; contradiction (i.e. 8r8c15) => r9c9 <> 4; stte.
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dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Mon Nov 09, 2020 8:08 pm    Post subject: Reply with quote

Btw, the hidden pair 58 in Peter's grid is sort of hard to find if you're just looking at candidates - but while cross-hatching it's easy to notice that the 5 and 8 are in rows 5 and 6 which means they must be in r4c46 (since r4c5 is already populated).
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storm_norm22



Joined: 24 Oct 2020
Posts: 15

PostPosted: Tue Nov 10, 2020 3:16 am    Post subject: Reply with quote

almost m-wing Cool

you would have this m-wing
(6=4)r9c9 - (4)r9c5 = (6-4)r8c4 = (4)r7c4
which would eliminate the 4 in r7c7 if the 6 in r8c5 didn't exist.
so following the 6's along (6)r8c5 - (6)r1c5 = (6)r1c89 - (6)r3c7 = (6-2)r8c7 = (2)r7c7

put it all together

m-wing[(6=4)r9c9 - (4)r9c5 = (6-4)r8c4 = (4)r7c4] = (6)r8c5 - (6)r1c5 = (6)r1c89 - (6)r3c7 = (6-2)r8c7 = (2)r7c7; r7c7 <>4

or if you prefer, you can see it as a contradiction using the 6's in box 8

Code:
6r8c4 - 4r8c4 = 4r7c4
||
6r8c5 - r1c5 = r1c89 - r3c7 = (6-2)r8c7 = (2)r7c7
||
6r9c5 - (6=4)r9c9


Code:
+-------------------+---------------------+----------------------+
| 589   579   1     | 2       789(6)  789 | 3      47(6)  489(6) |
| 389   2     36789 | 1689    36789   4   | 5      167    689    |
| 4     379   36789 | 1689    5       13  | 79(6)  167    2      |
+-------------------+---------------------+----------------------+
| 6     379   379   | 58      4       58  | 79     2      1      |
| 129   149   5     | 7       239     13  | 8      346    469    |
| 129   8     479   | 19      239     6   | 479    347    5      |
+-------------------+---------------------+----------------------+
| 7     6     489   | 89(4)   1       289 | 4(2)   5      3      |
| 1358  1345  348   | 58(46)  8(6)    258 | 4(26)  9      7      |
| 59    459   2     | 3       79(6)   579 | 1      8      (46)   |
+-------------------+---------------------+----------------------+
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Tue Nov 10, 2020 4:30 pm    Post subject: Reply with quote

Yes norm, used something related, believed it was an actual M-Wing, but I came to it via a different path. So many options and good rinsing/scanning skills needed in this one. Thanks again peter.

cheers...immp
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storm_norm22



Joined: 24 Oct 2020
Posts: 15

PostPosted: Tue Nov 10, 2020 4:57 pm    Post subject: Reply with quote

immpy wrote:
Yes norm, used something related, believed it was an actual M-Wing, but I came to it via a different path. So many options and good rinsing/scanning skills needed in this one. Thanks again peter.

cheers...immp


agreed, nice puzzle from peter
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