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Steve R
Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England
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 Posted: Mon Mar 31, 2008 3:38 pm Post subject: VH alternative |
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For those missing their VH fix, the Times puzzle 1823 is of a similar standard.
Steve |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Mon Mar 31, 2008 11:07 pm Post subject: |
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its no picnic through the basic box/line eliminations, neither the triples that show up.
x-wing on 6 first.
then this grid...
color the 2
| Code: | 29 26 5 | 3 8 7 | 4 69 1
3 1 69 |R25 4 25 | 679 79 8
47 8 47 | 9 6 1 | 23 35 25
------------------------------------------------------------------
6 4 R27 | 8 -279 25 | 579 1 3
257 257 1 | 6 279 3 | 789 4789 47
8 9 3 | 57 1 4 | 57 2 6
------------------------------------------------------------------
2479 237 69 | 1 5 8 | 2367 347 247
1 257 G247 |G27 3 6 | 278 4578 9
257 36 8 | 4 R27 9 | 1 36 257 |
the coloring eliminates the 2 in r2c4
leaves this coloring grid on candidate 2, also a fishy pattern...
| Code: | 29 26 5 | 3 8 7 | 4 69 1
3 1 69 |G25 4 R25 | 679 79 8
47 8 47 | 9 6 1 | 23 35 25
------------------------------------------------------------------
6 4 R27 | 8 79 G25 | 579 1 3
257 257 1 | 6 R279 3 | 789 4789 47
8 9 3 | 57 1 4 | 57 2 6
------------------------------------------------------------------
2479 237 69 | 1 5 8 | 2367 347 247
1 -257 G247 |R27 3 6 |-278 4578 9
257 36 8 | 4 G27 9 | 1 36 257 |
eliminates the 2 in r8c2 and r8c7...
this is simply a swordfish in col 3,4,6
that leaves a hidden {2,3} pair in col 7
edit: I realize the swordfish is there from the start, just wanted to show the steps in the coloring pattern along the way. |
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ravel
Joined: 21 Apr 2006
Posts: 536
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| Posted: Tue Apr 01, 2008 9:01 am Post subject: |
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It seems that the Times still gets the puzzles from Wayne Gould, who has made sudoku popular all over the world some years ago. At that time the only known advanced techniques have been x-wing and swordfish - and i suppose that Wayne never updated his program for other methods.
So, if you are stuck there, look for swordfish. But i dont like to do that, especially not on paper, because the search is cumbersome and boring.
I did not try this puzzle on paper, but probably i would have solved it something like that (after x-wing, xy-wing and kite):
| Code: | *------------------------------------------------*
|#29 26 5 | 3 8 7 | 4 #69 1 |
| 3 1 69 | 25 4 25 | 69 7 8 |
| 47 8 47 | 9 6 1 | 23 35 25 |
|-----------------+-------------+----------------|
| 6 4 27 | 8 9 25 | 57 1 3 |
| 257 257 1 | 6 27 3 | 89 #89 4 |
| 8 9 3 | 57 1 4 | 57 2 6 |
|-----------------+-------------+----------------|
|#2479 237 69 | 1 5 8 | 236 34 27 |
| 1 257 *247 | 27 3 6 | 28 *458 9 |
| 257 36 8 | 4 27 9 | 1 36 257 |
*------------------------------------------------*
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Useless skyscraper for 9, one of r7c1 and r5c8 must be 9.
r7c1=9 => r8c3=4
r5c8=9 => r8c8=8
In both cases r8c8<>4
[edit: corrected typo]
Last edited by ravel on Fri Apr 04, 2008 7:33 am; edited 1 time in total |
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Victor
Joined: 29 Sep 2005
Posts: 207
Location: NI
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| Posted: Tue Apr 01, 2008 12:58 pm Post subject: |
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| I used to like Brainbashers SH, apart from the occasional times when swordfish appeared - and I didn't then know any alternatives. (Still don't always see the alternatives, tho' I did this time.) Finding a non-SF solution made this a nice puzzle. |
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Steve R
Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England
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| Posted: Tue Apr 01, 2008 1:24 pm Post subject: |
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Ravel may well be right about Wayne Gould’s puzzles. Certainly his book of extreme puzzles soon went in the bin because of an excess of swordfish. However, the Times’ puzzles have been supplied by sudokusolver.com for a year or so now. This one be solved with straightforward techniques, which is why I chose it.
Starting from Norm’s first grid
| Code: | 29 26 5 | 3 8 7 | 4 69 1
3 1 69 | 25 4 25 | 679 79 8
47 8 47 | 9 6 1 | 23 35 25
------------------------------------------------------------------
6 4 27 | 8 279 25 | 579 1 3
257 257 1 | 6 279 3 | 789 4789 47
8 9 3 | 57 1 4 | 57 2 6
------------------------------------------------------------------
2479 237 69 | 1 5 8 | 2367 347 247
1 257 247 | 27 3 6 | 278 4578 9
257 36 8 | 4 27 9 | 1 36 257 |
7 can be eliminated from r4c5 using the xy-wing pivoted on r4c6 (either r4c3 or r6c4 contains 7). That reveals a finned x-wing for 7 in columns 2 and 5, so it can be eliminated from r9c1 as well.
An xyz-wing then completes the puzzle.
Steve |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Fri Apr 04, 2008 5:28 am Post subject: |
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| ravel wrote: | It seems that the Times still gets the puzzles from Wayne Gould, who has made sudoku popular all over the world some years ago. At that time the only known advanced techniques have been x-wing and swordfish - and i suppose that Wayne never updated his program for other methods.
So, if you are stuck there, look for swordfish. But i dont like to do that, especially not on paper, because the search is cumbersome and boring.
I did not try this puzzle on paper, but probably i would have solved it something like that (after x-wing, xy-wing and kite):
| Code: | *------------------------------------------------*
|#29 26 5 | 3 8 7 | 4 #69 1 |
| 3 1 69 | 25 4 25 | 69 7 8 |
| 47 8 47 | 9 6 1 | 23 35 25 |
|-----------------+-------------+----------------|
| 6 4 27 | 8 9 25 | 57 1 3 |
| 257 257 1 | 6 27 3 | 89 #89 4 |
| 8 9 3 | 57 1 4 | 57 2 6 |
|-----------------+-------------+----------------|
|#2479 237 69 | 1 5 8 | 236 34 27 |
| 1 257 *247 | 27 3 6 | 28 *458 9 |
| 257 36 8 | 4 27 9 | 1 36 257 |
*------------------------------------------------*
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Useless skyscraper for 9, one of r8c1 and r5c8 must be 9.
r8c1=9 => r8c3=4
r5c8=9 => r8c8=8
In both cases r8c8<>4 |
Ravel, shouldn't your cell be r7c1 ?? for the useless skyscraper??
so it should read "r7c1=9 => r8c3=4" |
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ravel
Joined: 21 Apr 2006
Posts: 536
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| Posted: Fri Apr 04, 2008 7:31 am Post subject: |
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Yes, thanks. But Steve R's solution is much better anyway  |
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