Help with XY-Chain

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Help with XY-Chain

Postby enxio27 » Tue Oct 27, 2015 9:42 pm

This is Grid 2 of the upper left section of a butterfly samurai puzzle by djape. I've completed all four of the other sections.

Code: Select all
.-------------------------------.-------------------------------.-------------------------------.
| 46        157       57        | 149       8         149       | 2         67        3         |
| 46        17        9         | 3         14        2         | 5         67        8         |
| 2         3         8         | 67        67        5         | 9         1         4         |
:-------------------------------+-------------------------------+-------------------------------:
| 13        48        134       | 478       9         3478      | 6         2         5         |
| 359       459       2         | 46        456       34        | 1         8         7         |
| 7         58        6         | 2         15        18        | 3         4         9         |
:-------------------------------+-------------------------------+-------------------------------:
| 139       479       1347      | 1479      147       6         | 8         5         2         |
| 158       2         157       | 1578      3         178       | 4         9         6         |
| 589       6         45        | 4589      2         489       | 7         3         1         |
'-------------------------------.-------------------------------.-------------------------------'


Richard Broughton's SudokuSolver gives me the following hint:

Grid 02: XY-Chain r5c4(4/6) - r3c4(6/7) - r4c4=r4c6

I haven't used XY chains yet, so I don't really understand what that hint is trying to tell me. Can someone please explain?
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Re: Help with XY-Chain

Postby SteveG48 » Tue Oct 27, 2015 11:33 pm

enxio27 wrote:This is Grid 2 of the upper left section of a butterfly samurai puzzle by djape. I've completed all four of the other sections.

Code: Select all
.-------------------------------.-------------------------------.-------------------------------.
| 46        157       57        | 149       8         149       | 2         67        3         |
| 46        17        9         | 3         14        2         | 5         67        8         |
| 2         3         8         | 67        67        5         | 9         1         4         |
:-------------------------------+-------------------------------+-------------------------------:
| 13        48        134       | 478       9         3478      | 6         2         5         |
| 359       459       2         | 46        456       34        | 1         8         7         |
| 7         58        6         | 2         15        18        | 3         4         9         |
:-------------------------------+-------------------------------+-------------------------------:
| 139       479       1347      | 1479      147       6         | 8         5         2         |
| 158       2         157       | 1578      3         178       | 4         9         6         |
| 589       6         45        | 4589      2         489       | 7         3         1         |
'-------------------------------.-------------------------------.-------------------------------'


Richard Broughton's SudokuSolver gives me the following hint:

Grid 02: XY-Chain r5c4(4/6) - r3c4(6/7) - r4c4=r4c6

I haven't used XY chains yet, so I don't really understand what that hint is trying to tell me. Can someone please explain?


I don't know anything about butterfly samurai puzzles, but what this hint is telling you is that:

If r5c4 is not a 4 then it's a 6,
then r3c4 can not be 6 so it's a 7 (that's the xy chain part),
then r4c4 cannot be 7, so r4c6 must be 7.

From that you can conclude that r4c6 is not a 4, because of r5c4 is not a 4 then r4c6 is a 7 (not a 4), and if r5c4 is a 4 then r4c6 cannot be a 4. Either way, r4c6 is not a 4.
Steve
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