## Almost XY Wing

Advanced methods and approaches for solving Sudoku puzzles
Would you give a little more explanation as to how you proceed from r1c5=9 to r9c5=1.
re'born

Posts: 551
Joined: 31 May 2007

rep'nA wrote:Would you give a little more explanation as to how you proceed from r1c5=9 to r9c5=1.

If r1c5<>1 then r9c5 must be 1. There is a strong link of 1 in those 2 cells.
udosuk

Posts: 2698
Joined: 17 July 2005

Doy.

Thanks udosuk.
re'born

Posts: 551
Joined: 31 May 2007

Also, easy Multi-Colors on <9> in [r1] and [c9] => [r5c5]<>9. Naked Pair and Singles follow.

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` *--------------------------------------------------------------------* | 4      2      7      | 3     #189    18     |#89     6      5      | | 35     35     6      | 2489   7      48     | 2489   1     *2489   | | 1      9      8      | 6      25     45     | 3      7      24     | |----------------------+----------------------+----------------------| | 35     7      345    | 4589   589    2      | 6      59     1      | | 6      8      1      | 579   -359    357    | 2579   4     *279    | | 9      45     2      | 1      6      457    | 578    3      78     | |----------------------+----------------------+----------------------| | 8      6      345    | 57     35     9      | 1      2      47     | | 2      135    359    | 578    4      13578  | 579    59     6      | | 7      145    459    | 25     125    6      | 459    8      3      | *--------------------------------------------------------------------*`
daj95376
2014 Supporter

Posts: 2624
Joined: 15 May 2006

daj95376 wrote:Also, easy Multi-Colors on <9> in [r1] and [c9] => [r5c5]<>9. Naked Pair and Singles follow.

Since this was a simple sudoku puzzle, that method had to exist. But it may be more difficult to look for multiple colours than to look for a xy-wing. If you can't find an xy-wing, you can sometimes make moves like this and then end up solving the puzzle any way. Solving the puzzle after the multi-colour move is a bit tougher than doing it after the move mentioned above.
Finlip

Posts: 49
Joined: 15 July 2005

rep'nA wrote:Would you give a little more explanation as to how you proceed from r1c5=9 to r9c5=1.

There is a strong link like udosuk said. If you don't see that strong link, look at the column and make the following observations in column 5.

I initially saw it like this.
r1c5<>9
r57c5=3&5
r3c5=2
r9c5=1
Finlip

Posts: 49
Joined: 15 July 2005

Finlip wrote:But it may be more difficult to look for multiple colours than to look for a xy-wing. If you can't find an xy-wing, you can sometimes make moves like this and then end up solving the puzzle any way. Solving the puzzle after the multi-colour move is a bit tougher than doing it after the move mentioned above.

Although that move was termed "multiple colours", it was actually a simple 5-cell turbot fish which is much much easier than xy-wing & such...

Carcul might like to express it as a simple nice loop:
[r5c5]-9-[r1c5]=9=[r1c7]-9-[r2c9]=9=[r5c9]-9-[r5c5]

Therefore r5c5<>9...

For people who like to use strong links it's definitely a lot easier than xy-wings or your chain...
udosuk

Posts: 2698
Joined: 17 July 2005

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