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daj95376
Joined: 23 Aug 2008
Posts: 3854
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 Posted: Fri Jan 22, 2010 1:56 am Post subject: Puzzle 10/01/21 (A) |
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Warm up.
| Code: | +-----------------------+
| 2 . . | . 9 . | . . . |
| . 4 . | . 2 . | . 9 5 |
| . . 7 | . . . | 4 . . |
|-------+-------+-------|
| . . . | 6 . . | . 5 . |
| 8 5 . | . 7 . | 2 . . |
| . . . | . . 5 | . 1 3 |
|-------+-------+-------|
| . . 6 | . 4 . | 5 . . |
| . 8 . | 1 . 2 | . 6 . |
| . 1 . | . . 9 | . . . |
+-----------------------+
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Play this puzzle online at the Daily Sudoku site |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sat Jan 23, 2010 6:19 am Post subject: |
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| I was ready to throw in the towel, but I decided to play what I thought was a useless move, a Hidden UR on 16. That opened up an XYZ (137), XY (673), Type 2 UR (37-8) and an XYZ (357). |
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Sat Jan 23, 2010 12:16 pm Post subject: |
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| Marty: Two steps. One VH and the other VH+. |
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tlanglet
Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills
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| Posted: Sat Jan 23, 2010 2:29 pm Post subject: |
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I found a move that looks like a xyz-wing but has four digits in the pivot cell.
| Code: | *-----------------------------------------------------------*
| 2 36 5 | 4 9 1-368 | 16 378 78 |
| 136 4 8 | 37 2 #1367 | 16 9 5 |
| 1369 369 7 | 358 135 1-368 | 4 238 28 |
|-------------------+-------------------+-------------------|
| 37 237 1239 | 6 13 4 | 789 5 789 |
| 8 5 13 | 9 7 13 | 2 4 6 |
| 467 67 49 | 2 8 5 | 79 1 3 |
|-------------------+-------------------+-------------------|
| 379 2379 6 | 378 4 378 | 5 278 1 |
| 3457 8 34 | 1 35 2 | 379 6 479 |
| 3457 1 234 | 3578 6 9 | 378 278 2478 |
*-----------------------------------------------------------* |
The pivot cell is r2c6 containing the digits 1367, marked #.
(1)r2c6 - (1=3)r5c6 - (3)r1c6,
(3)r2c6 - (3)r1c6,
(6)r2c6 - (6)r2c7 = (6)r1c7 - (6=3)r1c2 - (3)r1c6,
(7)r2c6 - (7=3)r2c4 - (3)r1c6.
All four values in r2c6 result in r1c6<>3
BUT WAIT, THERE'S MORE!!
Now look at the same pivot cell again.
(1)r2c6 - (1=3)r5c6 - (3)r3c6,
(3)r2c6 - (3)r3c6,
(6)r2c6 - (6)r2c7 = (6)r1c7 - (6=3)r1c2 - (3)r1c8 = (3)r3c8 - (3)r3c6,
(7)r2c6 - (7=3)r2c4 - (3)r3c6.
All four values in r2c6 result in r3c6<>3.
Neither of these two moves seemed to help solve the puzzle, but are unusual. Is this just a one-time weird circumstance, or is it a recognized pattern?
My solution was a three stepper.
xy-wing -367
kite 3,
a Type 1 6-cell DP in r123c167.
Ted |
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Sat Jan 23, 2010 6:26 pm Post subject: |
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Ted,
Congratulations on your find!
Your technique is a "forcing chain with four streams" from a single cell. This approach is seldom used anymore ... especially since everyone wants to pack everything into as complicated of an AIC as they can create. The only time I see forcing chains used is when a UR is involved and there are a couple of extra candidates present.
Your solution can be compacted some.
| Code: | (1)r2c6 - (1=3)r5c6 - (3)r13c6
(3)r2c6 - (3)r13c6
(7)r2c6 - (7=3)r2c4 - (3)r13c6
(6)r2c6 - (6)r2c7 = (6)r1c7 - (6=3)r1c2 - (3)r1c6
|| - (3)r1c8 = (3)r3c8 - (3)r3c6
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Personally, I like forcing chains ... but I use them on a single candidate value across all the cells containing it in a row/column/box.
Regards, Danny
----- ----- ----- ----- -----
I can't believe the solutions for this puzzle. I really meant it when I called it a "warm up" puzzle.
| Code: | <67+3> XY-Wing r6c2/r1c2+r4c1 <> 3 r23c1,r4c2
r5c5 2-String Kite <> 3 r8c3 -or-
r7c5 2-String Kite <> 3 r4c1
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The XY-Wing seems to have been the stumbling block. Hmmm. |
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