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ffred
Joined: 29 Oct 2012
Posts: 19
Location: Kent, Egland
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 Posted: Sun Nov 04, 2012 10:36 pm Post subject: Swordfish challenges |
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Keith suggested posting puzzles that seemed to need a swordish:
http://www.dailysudoku.com/sudoku/forums/viewtopic.php?p=31626&sid=3efa30cb40f3a2f3285828d231a16763#31626
This is Menneske 6912567.
| Code: |
+-------+-------+-------+
| . . . | . . 6 | 9 . . |
| . . 9 | . 3 . | . . . |
| 6 8 . | . . . | . . 4 |
+-------+-------+-------+
| . . . | . 1 . | 6 . 5 |
| . . . | . . 8 | . 1 . |
| . 2 8 | . . . | 7 . . |
+-------+-------+-------+
| 4 . . | . 8 . | . 5 6 |
| 2 . . | . 9 . | . . . |
| . . 5 | 3 . . | . . . |
+-------+-------+-------+
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Play this puzzle online at the Daily Sudoku site
In case you prefer your grid post-basics:
| Code: |
+------------------+-------------------+-----------------+
| 357 13457 12347 | 124578 2457 6 | 9 237 12378 |
| 57 1457 9 | 124578 3 12457 | 1258 6 1278 |
| 6 8 1237 | 12579 257 12579 | 1235 237 4 |
+------------------+-------------------+-----------------+
| 379 347 347 | 2479 1 23479 | 6 8 5 |
| 3579 34567 3467 | 479 47 8 | 234 1 239 |
| 1 2 8 | 4569 456 3459 | 7 349 39 |
+------------------+-------------------+-----------------+
| 4 9 137 | 127 8 127 | 123 5 6 |
| 2 1367 1367 | 14567 9 1457 | 1348 347 1378 |
| 8 167 5 | 3 2467 1247 | 124 2479 1279 |
+------------------+-------------------+-----------------+
|
Play this puzzle online at the Daily Sudoku site
Challenge 1. I couldn't crack this puzzle without using the swordfish. Can you?
(You can achieve the same deletions as the swordfish with a loop as is sometimes (often?) the case:-
(2)r9c8 = r13c8 - r2c79 = r2c46 - r13c5 = r9c5 - loop
But that doesn't seem any easier and so doesn't count!)
Challenge 2. The swordfish merely made a little dent in the puzzle, though just enough. But it still required many moves. Can anyone see a killer move or two that makes the solution not too long? |
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JC Van Hay
Joined: 13 Jun 2010
Posts: 494
Location: Charleroi, Belgium
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| Posted: Mon Nov 05, 2012 1:21 pm Post subject: |
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The Swordfish, rather than its elimination(s), shows the path ...
#1. "basics"
5 Singles : r6c1=1, r2c8=6, r4c8=8=r9c1, r7c2=9
1-fish(2B6) : 2r5c7=2r5c9 :=> -2r5c45
3-fish(2C358) : 2r3c3=2r1c3-2r1c58=XWing[2r3c5=2r3c8-2r9c8=2r9c5] Loop :=> -2r139c4679
2-fish(3R37) : no elimination
1-fish(5B4) : 5r5c1=5r5c2 :=> -5r5c45
1-fish(6B4) : 6r5c2=6r5c3 :=> -6r5c45
#2. Analysis of the B/B-Plot shows that the strongest digits are 2 and 6. Furthermore, they are weakly coupled in r9c5 ...
Fortunately, r9c5=2->contradiction, while r9c8=2->solution, using only singles.
Correspondingly, a chain[15] not requiring the Swordfish may be written as :
| Code: | +---------------------+---------------------------+-----------------------+
| 357 13457 12347 | 124578 2457 6 | 9 237 12378 |
| 57 1457 9 | 124578 3 12457 | 1258 6 1278 |
| 6 8 127(3) | 12579 257 12579 | 125(3) 27(3) 4 |
+---------------------+---------------------------+-----------------------+
| 379 347 347 | 2479 1 23479 | 6 8 5 |
| 3579 34567 3467 | 479 47 8 | 4(23) 1 (239) |
| 1 2 8 | -9(56-4) (456) 39(45) | 7 (349) (39) |
+---------------------+---------------------------+-----------------------+
| 4 9 17(3) | 17(2) 8 17(2) | 1(23) 5 6 |
| 2 1367 1367 | 17(456) 9 17(45) | 1348 (347) 1378 |
| 8 167 5 | 3 7-2(46) 127(4) | (124) 2479 (1279) |
+---------------------+---------------------------+-----------------------+
15 Truths = {3R3 2R5 456R6 23R7 5R8 8N8 9N79 39B6 46B8}
22 Links = {24r9 2c7 3c378 4c68 5c6 6c5 9c9 5n9 6n4589 8n46 9n5 2b8 17b9}
3 Eliminations --> [r6c4<>49 : not required], r9c5<>2
or
6r9c5=6r8c4
5r8c4=5r8c6
4r9c5=4r8c4=4r8c6=4r9c6----------------------------------------------------------------------AAHS(456)B8
2r9c7=============4r9c7=1r9c7
6r6c4===================6r6c5
5r6c6=============5r6c5=5r6c4
4r6c6=======4r6c5=4r6c4=4r6c8----------------------------------------------AAHS(456)R6
9r6c8=9r56c9
2r9c9===================1r9c9===================9r9c9==7r9c9
4r8c8========7r8c8=3r8c8
3r7c7=3r7c3
3r3c8=3r3c3=3r3c7---------------FXW(3R37)
3r6c8=======3r5c7=3r56c9
9r6c8================================9r56c9--------HP(39)r56c9
2r5c9==2r5c7
2r7c46================================================================================2r7c7
=> 4r9c5=6r9c5=2r9c79=2r7c46 :=> -2r9c5 |
If the Swordfish isn't done first, what remains of it then leads to : 2-fish(2r13c35) :=> r9c8=2; Singles to the end
Alternatively, for example, but after some hard work :
#2. Chain[3] : 4r5c7=(4-9)r6c8=(9-2)r9c8=2r7c7 :=> r5c9=2; 1-fish(9B6) :=> -9r646
#3. Chain[8] : Kraken (347)r8c8 => 3r3c7=3r7c7=4r5c7 :=> -3r5c7; 6 Singles
| Code: | +----------------------+-----------------------+---------------------+
| 357 13457 12347 | 14578 2457 6 | 9 237 1378 |
| 57 1457 9 | 124578 3 12457 | 1258 6 178 |
| 6 8 127(3) | 1579 257 1579 | 15(3) 27(3) 4 |
+----------------------+-----------------------+---------------------+
| 379 347 347 | 2479 1 23479 | 6 8 5 |
| 3579 34567 3467 | 479 47 8 | -3(4) 1 2 |
| 1 2 8 | 456 456 345 | 7 3(49) 39 |
+----------------------+-----------------------+---------------------+
| 4 9 1(37) | 127 8 127 | 12(3) 5 6 |
| 2 136(7) 136(7) | 14567 9 1457 | 1348 (347) 1378 |
| 8 1(67) 5 | 3 47(26) 147 | 14 47(29) 179 |
+----------------------+-----------------------+---------------------+
8 Truths = {2R9 3R37 6R9 9C8 8N8 4B6 7B7}
11 Links = {7r8 3c378 4c8 5n7 6n8 7n3 9n258}
1 Elimination --> r5c7<>3
or
3r8c8-3r3c8=*XWing[3r3c7=*3r3c3-3r7c3=3r7c7]
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4r3c8-4r6c8=4r5c7
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7r8c8-7r8c23=*[3r7c7=(3-7)r7c3=*(7-6)r9c2=(6-2)r9c5=(2-9)r9c8=(9-4)r6c8=4r5c7] |
#4. 2-fish(1R3C2) : 1r3c4=1r3c3-1r12c2=1r8c2 :=> -1r8c4
#5. Loop[3] : 2r2c6=(2-5)r2c7=5r3c7-(5=2)r3c5 :=> -8r2c7,-5r3c4,-2r1c5; 1-fish and Locked Subsets to the end. |
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ffred
Joined: 29 Oct 2012
Posts: 19
Location: Kent, Egland
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| Posted: Tue Nov 06, 2012 8:51 pm Post subject: |
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JC, as I said in another post, that's seriously clever.
I'm going to work through your solutions, though they're at or beyond my limit of understanding. Anyway, thanks! |
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