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VH Nov 23rd

 
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Mogulmeister



Joined: 03 May 2007
Posts: 1151

PostPosted: Tue Nov 23, 2021 8:54 am    Post subject: VH Nov 23rd Reply with quote

Code:

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

Play this puzzle online at the Daily Sudoku site
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TomC



Joined: 30 Oct 2020
Posts: 349
Location: Wales

PostPosted: Tue Nov 23, 2021 9:04 am    Post subject: Reply with quote

X wing on 3's solves this
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Mogulmeister



Joined: 03 May 2007
Posts: 1151

PostPosted: Tue Nov 23, 2021 9:09 am    Post subject: Reply with quote

Code:

+--------------+--------------+--------------+
| 1   35  25   | 8   4   39   | 257 6   579  |
| 346 7   56   | 39  1   2    | 8   59  459  |
| 24  9   8    | 5   7   6    | 24  1   3    |
+--------------+--------------+--------------+
| 9   8   1    | 37  5   4    | 367 2   67   |
| 36  4   67   | 1   2   8    | 357 579 579  |
| 23  35  257  | 379 6   39   | 1   4   8    |
+--------------+--------------+--------------+
| 5   2   4    | 6   3   7    | 9   8   1    |
| 7   1   9    | 2   8   5    | 46  3   46   |
| 8   6   3    | 4   9   1    | 57  57  2    |
+--------------+--------------+--------------+


After basics.

Quote:
Hint: An X wing for 3's (column 2,6) or a swordfish for 3's (row 2,4,5).
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Mogulmeister



Joined: 03 May 2007
Posts: 1151

PostPosted: Tue Nov 23, 2021 9:25 am    Post subject: Reply with quote

Just for a diversion but to encourage those of you who should be exploring the dark side of sudoku:

If you say r6c1 = 3 you will put two 3's in box 2.

R6c1 < > 3

Which is the same elimination you might make with the X wing and the Swordfish but provides a different way of looking at the puzzle.
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TomC



Joined: 30 Oct 2020
Posts: 349
Location: Wales

PostPosted: Tue Nov 23, 2021 9:48 am    Post subject: Reply with quote

r4c7 <> 3

as then r4c9=6, r8c9=4, r3c7=4, r3c1=2, r6c1=3 leads to no 3's in box 5
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Mogulmeister



Joined: 03 May 2007
Posts: 1151

PostPosted: Tue Nov 23, 2021 1:42 pm    Post subject: Reply with quote



I've shown the above contradictions in pictorial form - they either put too many 3's in one box or remove them altogether in another.

You can also form a loopback to your start point which also shows that the number you started with is wrong.

a)Start in the red square and make it 3 then follow the pink squares:

r6c1 IS 3, r2c1 < > 3, r2c4 = 3, r1c6 < >3, r6c6 = 3 and r6c1 (red) NOT 3.

Start with 3 follow the loop around and the 3 you began with is out.

b)Start in the green square and make it 3 then follow the blue squares:

r4c7 IS 3 (not 6), r8c7 = 6 (not 4), r3c7 = 4, r3c1 = 2, r6c1 = 3 (not 2)
r5c1 = not 3, r5c7 = 3 and r4c7 NOT 3.

Again, start with 3 follow the loop around and the 3 you began with is out.
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