dailysudoku.com

keith · Posted: Sat Oct 27, 2007 9:34 pm Post subject: A learning experience

LA Times 040606

Asellus · Posted: Sun Oct 28, 2007 1:47 am Post subject:

I have no idea what re'born's "incredible move" is, but I like a nice challenge. So, I found a very interesting DP solution. Basics get one here, I believe:

+-----------------+--------------+-----------+


| 3689   39  368  | 89  5    2   | 7  1   4  |


| 79     2   4    | 79  3    1   | 5  8   6  |


| 78     5   1    | 4   6    78  | 3  9   2  |


+-----------------+--------------+-----------+


| 35678  37  3568 | 1   2    578 | 4  57  9  |


| 5789   79  58   | 6   78   4   | 1  2   3  |


| 1      4   2    | 3   9    57  | 8  6   57 |


+-----------------+--------------+-----------+


| 45     1   9    | 78  478  6   | 2  3   57 |


| 2      6   7    | 5   1    3   | 9  4   8  |


| 345    8   35   | 2   47   9   | 6  57  1  |


+-----------------+--------------+-----------+

The potential DP is in red. Note that the <4>s form an X-Wing.

If R4C6 is <5>, the DP results. But also, if R4C6 is <7>, the DP results. (R5C5 would be <8> and R9C3 would be <3>, if you need help seeing this.) So, R4C6 must be <8>.

This solves the puzzle.

keith · Posted: Sun Oct 28, 2007 2:11 pm Post subject:

What is a DP?

Basics get you here:

storm_norm · Joined: 18 Oct 2007 Posts: 1741

disjointed pair?

nataraj · Posted: Sun Oct 28, 2007 3:49 pm Post subject:

DP = deadly pattern.

I think what box 5 does is something like an ER (empty rectangle).
If r3c6=7 then none of c6=7 then r5c5=7.
Your chain, keith, looks to me like a grouped AIC where a group of cells act like one single cell for the purpose of the chain.

nataraj · Posted: Sun Oct 28, 2007 3:54 pm Post subject:

BTW, I did a coloring elimination of '8' in r5c1 first (probably unnecessary), then used an xy-chain (one of many, many, many many ... xy chains available) to remove 5 from r4c6 and r6c9:

(r4c8=7)=>(r4c2=3)=>(r1c2=9)=(r1c4=8 )=>(r3c6=7)=>(r6c6=5)

keith · Posted: Sun Oct 28, 2007 4:42 pm Post subject:

Deadly Pattern. I see it now.

A slightly different way to argue it is that to avoid the DP, R4C6 is <8>, and / or R7C5 is <8>, and / or R9C1 is <3>. Either of these forces the X-wing to have <4> in R7C1 and R9C5. This is not as direct as Asellus' solution, for you still need a (real) remote pair to finish it up.

You can also argue that each of R7C5 is <8>, R9C1 is <3>, force R4C6 to be <8>. Therefore, R4C6 must be <8>. R7C5 is easy, R9C1 is much longer, almost equivalent to solving the puzzle. (In the solution, all of the DP busters are true: R4C6 is <8> and R7C5 is <8> and R9C1 is <3>.)

Keith

keith · Posted: Wed Oct 31, 2007 11:06 pm Post subject:

From re'born, on the history: