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Dec 08 VH

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ZeroAssoluto

Joined: 05 Feb 2017
Posts: 933
Location: Rimini, Italy

Posted: Thu Dec 08, 2022 10:47 am Post subject: Dec 08 VH

Hi everyone,

Code:

+-----------+------------+-----------+
| 78 6 9 | 45 2 457 | 58 1 3 |
| 4 3 2 | 8 1 56 | 9 7 56 |
| 178 5 17 | 9 67 3 | 68 2 4 |
+-----------+------------+-----------+
| 6 1 3 | 2 57 57 | 4 9 8 |
| 2 4 8 | 6 9 1 | 3 5 7 |
| 9 7 5 | 3 4 8 | 2 6 1 |
+-----------+------------+-----------+
| 3 9 14 | 7 56 456 | 15 8 2 |
| 157 8 6 | 15 3 2 | 157 4 9 |
| 157 2 147 | 145 8 9 | 1567 3 56 |
+-----------+------------+-----------+

Play this puzzle online at the Daily Sudoku site

Quote:

XY-Wing
5,6,7 in r2c6,r34c5 and -5 in r4c6
or
5,6,7 in r24c6,r3c5 and -7 in r1c6,r4c5
or
XYZ-Wing 4,5,7 in r1c46,r4c6 and -5 in r2c6
or
W-Wing 5,6 in r2c6,r7c5 SL with number 5 in r4c56 and -6 in r3c5,r7c6

Ciao Gianni

TomC

Joined: 30 Oct 2020
Posts: 358
Location: Wales

Posted: Thu Dec 08, 2022 1:48 pm Post subject: Another way you could solve

Remove <1> from r7c3 to solve

Code:

+----------------+--------------+-------------+
| b78 6 9 | 45 2 457 | c58 1 3 |
| 4 3 2 | 8 1 56 | 9 7 56 |
| 178 5 a17 | 9 67 3 | 68 2 4 |
+----------------+--------------+-------------+
| 6 1 3 | 2 57 57 | 4 9 8 |
| 2 4 8 | 6 9 1 | 3 5 7 |
| 9 7 5 | 3 4 8 | 2 6 1 |
+----------------+--------------+-------------+
| 3 9 x14 | 7 56 456 | d15 8 2 |
| 157 8 6 | 15 3 2 | 157 4 9 |
| 157 2 147 | 145 8 9 | 1567 3 56 |
+----------------+--------------+-------------+

Quote:

XY chain abcd gives pincers of <1> in a + d to remove <1> from x

Greenvilleguy

Joined: 01 Jul 2022
Posts: 24
Location: US

Posted: Sat Dec 10, 2022 6:07 pm Post subject:

I see why r7c3 cannot be a 1, but I don't understand how you found it. Is is a pattern you are looking for like an xy - wing?

TomC

Joined: 30 Oct 2020
Posts: 358
Location: Wales

Posted: Sun Dec 11, 2022 10:31 am Post subject:

Greenvilleguy wrote:

I see why r7c3 cannot be a 1, but I don't understand how you found it. Is is a pattern you are looking for like an xy - wing?

Yes, this is all about patterns, Gianni's first XY wing is <57> <67> <56> to eliminate <5> from r4c6, but this is also a XY chain of length 3 where either end of the chain is <5>

My XY chain is <17> <78> <58> <15> giving <1> at either end of the chain

I generally see XY wings and XY chains as contradictions, in this case scan the entire grid and only concentrate on cells which contain two candidates can help to indentify these patterns

So my solution could also be seen as : if d=5, c=8, b=7, a=1 leads to no <1> in row 7

Note that there is a very similar XY chain of length 5 which does the same thing ( <17> <67> <68> <58> <15> )

Greenvilleguy

Joined: 01 Jul 2022
Posts: 24
Location: US

Posted: Sun Dec 11, 2022 11:34 pm Post subject:

Thanks, that's very helpful.

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