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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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 Posted: Sat Dec 05, 2009 11:35 pm Post subject: Free Press Dec 4, 2009 |
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Not yet solved. | Code: | Puzzle: FP120409
+-------+-------+-------+
| . . . | . . . | . . . |
| 7 . 3 | 1 . . | . 6 5 |
| . 1 . | 6 8 9 | . . . |
+-------+-------+-------+
| . . 8 | . . 2 | 7 . . |
| 2 5 . | . . . | . 8 3 |
| . . 6 | 4 . . | . . . |
+-------+-------+-------+
| . . . | 3 4 6 | . 7 . |
| 3 . . | . . . | 5 . 1 |
| . . . | . . . | . . . |
+-------+-------+-------+ |
So far, two advanced moves.
Keith |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Sun Dec 06, 2009 8:07 am Post subject: |
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| Code: | +----------------+------------+--------------------+
| 6 289 29 | 57 57 3 | 1489 149 489 |
| 7 89 3 | 1 2 4 | 89 6 5 |
| 4 1 5 | 6 8 9 | -2(3) 23 7 |
+----------------+------------+--------------------+
| 19 34 8 | 59 356 2 | 7 149 469 |
| 2 5 7(4) | 79 67 1 | 9(46) 8 3 |
| 19 37 6 | 4 37 8 | 19(2) 5 9(2) |
+----------------+------------+--------------------+
| 5 9(2) 1 | 3 4 6 | 89(2) 7 89(2) |
| 3 6 (24) | 8 9 7 | 5 24 1 |
| 8 47 479 | 2 1 5 | 49(36) 349 469 |
+----------------+------------+--------------------+ |
almost x-wing on 2's in r67c79 if the 2 in r7c2 is false.
[x-wing(2)r67c79] = (2)r7c2 - (2=4)r8c3 - (4)r5c3 = (4-6)r5c7 = (6-3)r9c7 = (3)r3c7; r3c7 <> 2
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Sun Dec 06, 2009 11:10 pm Post subject: |
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| Code: | r58c3 Skyscraper <> 4 r9c7,r4c8
r2c3 2-String Kite <> 9 r9c7
probably the point where Keith stopped
+--------------------------------------------------------------+
| 6 289 29 | 7 5 3 | 1489 149 489 |
| 7 89 3 | 1 2 4 | 89 6 5 |
| 4 1 5 | 6 8 9 | g23 a23 7 |
|--------------------+--------------------+--------------------|
| 19 34 8 | 5 36 2 | 7 19 46 |
| 2 5 d47 | 9 67 1 | e46 8 3 |
| 19 37 6 | 4 37 8 | 129 5 29 |
|--------------------+--------------------+--------------------|
| 5 29 1 | 3 4 6 | 289 7 289 |
| 3 6 c24 | 8 9 7 | 5 b24 1 |
| 8 47 479 | 2 1 5 | f36 349 469 |
+--------------------------------------------------------------+
# 43 eliminations remain
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The best my solver found was a chain using many of the cells used by Norm.
(2)r3c8 = (2-4)r3c8 = r8c3 - r5c3 = (4-6)r5c7 = (6-3)r9c7 = (3)r3c7 => r3c7<>2, r3c8<>3
It sure would be interesting to see the solution obtained by the originator of this Free Press puzzle. I wonder if it's the same approach as used by oaxen. |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Sun Dec 06, 2009 11:34 pm Post subject: |
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| daj95376 wrote: |
It sure would be interesting to see the solution obtained by the originator of this Free Press puzzle. I wonder if it's the same approach as used by oaxen. |
If you go to the LA Times site, where they publish the same puzzle as the Free Press, they do identify the source of the puzzles.
Maybe we should ask them what the solution path is? (I'll try.)
What is "oaxen's approach"?
Keith |
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Sun Dec 06, 2009 11:57 pm Post subject: |
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| keith wrote: | What is "oaxen's approach"?
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Start reading here. |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Mon Dec 07, 2009 12:40 am Post subject: |
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| daj95376 wrote: | | keith wrote: | What is "oaxen's approach"?
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Start reading here. |
Oh. Whatever turns you on.
By my definition, at any given state of a puzzle, a "backdoor" is a single digit in a single unsolved cell that will then solve the puzzle with only basic moves.
There are solvers (including, it seems, Danny's) that identify these backdoor digits. This is useful if you are engaging in our strut-your-stuff game of constructing one-steppers. It tells you which cells or digits to go after.
It is also useful in attacking very difficult puzzles. It gives you some idea of where to mount an attack.
Now, if you are simply going to choose possible digits, by all means pick them in bivalue cells. You have a 50% chance of picking the one that is correct.
Keith
Last edited by keith on Mon Dec 07, 2009 4:24 pm; edited 1 time in total |
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Mogulmeister
Joined: 03 May 2007
Posts: 1151
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| Posted: Mon Dec 07, 2009 3:48 pm Post subject: |
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What I like about Norm's approach is the way that he takes in "almost" structures and extrapolates with adjoining strong links. Combining "patterns" with "chains" (note the quotes) to make eliminations.
This feels "hybrid" in that it can appeal to the visual/spatial mind as well as the chaining one. You also feel that these could be spottable without a solver. |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Tue Dec 08, 2009 1:14 am Post subject: |
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keith wrote:
| Quote: | There are solvers (including, it seems, Danny's) that identify these backdoor digits. This is useful if you are engaging in our strut-your-stuff game of constructing one-steppers. It tells you which cells or digits to go after.
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Mogulmeister wrote:
| Quote: | | You also feel that these could be spottable without a solver. |
its a little of both.
the reason is because when I scan a grid which I assume can't be solved with one advanced step then I am not scanning the grid for advanced steps. instead, I concentrate on the those cells or candidates which I feel will do the most damage and look for a way to target those candidates or cells.
in this puzzle's example, I saw the almost x-wing structure and how it targeted the bi-value cell {2,3} in r3c7. so instead of pulling a pattern out of the rubble, I let the rubble show me a pattern and it was kind enough to give me a target as well. it shouldn't be that much of a stretch in imagination to let an almost x-wing do the targeting because a x-wing is standard procedure for this forum and its puzzles. |
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