The New Sudoku Players' Forum

[Kacpercat]

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

[JasonLion]

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.

[Kacpercat]

>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

[enxio27]

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.

[ArkieTech]

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

[7b53]

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 ?

[JasonLion]

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.