well of course, I need a hint

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well of course, I need a hint

Postby Kacpercat » Wed Nov 07, 2012 12:31 pm

Hello everybody.
I am very happy to find this forum. I am a recent sudoku fan and I know the basic techniques but it looks like I have just reached a certain border difficult to cross. My iPad sudoku app ranks the attached board as the easiest of several expert levels. Yellow numbers are the fields solved by me, white are original numbers of this game. Could you just give me a hint what to do now? what is the strategy to apply? I will be very happy to hear from you. Kacpercat
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Re: well of course, I need a hint

Postby JasonLion » Wed Nov 07, 2012 1:15 pm

The next step is an X-Wing on 2s, though it is going to take more than that to solve the puzzle. After that, a Sashimi X-WIng is one of the ways to proceed.
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Re: well of course, I need a hint

Postby Kacpercat » Wed Nov 07, 2012 1:23 pm

>The next step is an X-Wing on 2s, though it is going to take more than that to solve the puzzle. After that, a Sashimi X-WIng is one of the ways to proceed.

Haha thank you Mr Lion, it is a very concise information. I could expect it to be an X-wing but there are 16 fields with 2s and I can't find which of the I should X-wing :)
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Re: well of course, I need a hint

Postby enxio27 » Wed Nov 07, 2012 1:43 pm

Kacpercat wrote:I could expect it to be an X-wing but there are 16 fields with 2s and I can't find which of the I should X-wing :)

That is left as an exercise for the reader. If you are familiar with the X-wing technique, you will spot it easily. If not, you need to go back and review the technique.
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Re: well of course, I need a hint

Postby ArkieTech » Wed Nov 07, 2012 2:04 pm

a sashimi x-wing will solve it with one step and singles.

Code: Select all
 *-----------*
 |.67|3..|..5|
 |3..|.9.|.7.|
 |1..|...|..3|
 |---+---+---|
 |9..|.2.|.3.|
 |.1.|5.3|24.|
 |...|.41|...|
 |---+---+---|
 |...|.6.|.5.|
 |.8.|75.|9..|
 |6.9|...|...|
 *-----------*
 *-----------------------------------------------------------*
 |a248   6     7     | 3     1     24-8  | 48    9     5     |
 | 3     24    458   | 2468  9     56    | 1     7     248   |
 | 1     9     458   | 248  d78    57    | 468   268   3     |
 |-------------------+-------------------+-------------------|
 | 9     47    48    | 68    2     67    | 5     3     1     |
 |b78    1     6     | 5    c78    3     | 2     4     9     |
 | 5     3     2     | 9     4     1     | 678   68    78    |
 |-------------------+-------------------+-------------------|
 | 247   247   1     | 248   6     9     | 3     5     248   |
 | 24    8     3     | 7     5     24    | 9     1     6     |
 | 6     5     9     | 1     3     248   | 478   28    2478  |
 *-----------------------------------------------------------*
sashimi x-wing
8r1c1=r5c1-r5c5=r3c5 => -8r1c6; stte
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Re: well of course, I need a hint

Postby 7b53 » Thu Nov 08, 2012 2:19 am

Code: Select all
 ------------------------------------------------------------*
 |a248   6     7     | 3     1     24-8  | 48    9     5     |
 | 3     24    458   | 2468  9     56    | 1     7     248   |
 | 1     9     458   | 248  d78    57    | 468   268   3     |
 |-------------------+-------------------+-------------------|
 | 9     47    48    | 68    2     67    | 5     3     1     |
 |b78    1     6     | 5    c78    3     | 2     4     9     |
 | 5     3     2     | 9     4     1     | 678   68    78    |
 |-------------------+-------------------+-------------------|
 | 247   247   1     | 248   6     9     | 3     5     248   |
 | 24    8     3     | 7     5     24    | 9     1     6     |
 | 6     5     9     | 1     3     248   | 478   28    2478  |
 *-----------------------------------------------------------*
sashimi x-wing
8r1c1=r5c1-r5c5=r3c5 => -8r1c6; stte


is really the two end cells that lead to the eliminations.
in this case, the two end cells will be (r1c1 and r3c5). meaning one of them must be true.
so whatever cells can "see" both (r1c1 and r3c5) cannot be that value.
a total of six cells {r3c123 , r1c456}

(x-wing, skyscraper, two string kite, empty rect, sashimi-x, fin-x, etc)
these are all part of the single digit pattern or simple colouring.
is just different ways to spot them for their names.

does anyone agree ?
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Re: well of course, I need a hint

Postby JasonLion » Thu Nov 08, 2012 3:05 am

Yes, and no. X-Wings are a kind of special case, being both fish and chains/coloring. Certainly it is true that every X-Wing is equivalent to a chain or a coloring. But at the same time, thinking of X-WIngs as "only" chains/coloring loses the generalization to higher order fish, which do not follow from chains/coloring.

Meanwhile, in a very different sense, each of the techniques you mention has a unique approach for locating occurrences, each of which is simpler than coloring. Logically, they are the same as coloring, but in practice they each allow for a unique approach to spotting and are potentially much faster/simpler to spot than any more general approach based on traditional coloring.
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