## can somone please explain this to me better

Advanced methods and approaches for solving Sudoku puzzles

### can somone please explain this to me better

i am really confused about the methods of solving the more complicted sudokus i only can solve the sudokus that use cross hatching and other easy methods but i dont get how x wing and other more difficult ways work i have looked on the internet but all the explantions are confusing... can somone please explain in a way that i can understand?
Kunegochu

Posts: 47
Joined: 20 January 2008

Kunegochu wrote:i am really confused about the methods of solving the more complicted sudokus

i only can solve the sudokus that use cross hatching and other easy methods
but i dont get how x wing and other more difficult ways work

i have looked on the internet
but all the explantions are confusing...

can somone please explain in a way that i can understand?

hi Kunegochu

X-wing is explained here

Pat

Posts: 3690
Joined: 18 July 2005

### Can someone please explain this to me better

Hi Kunegochu,

Notwithstanding various descriptions of the X-Wing pattern throughout the forum I too had trouble understanding this technique. Thanks to another member whose name I've misplaced, I came across the following explanation which helped me considerably.

The X-Wing pattern requires a particular candidate to appear twice and only twice either in two rows and sharing the same two columns in which case the eventual exclusions of an identical candidate occur in these same two columns or, using the same logic, where a particular candidate appears twice and only twice in two columns and sharing the same two rows then the exclusions occur in rows.

In the following grid, the 3's form an X-Wing pattern in rows 6 and 9, columns 3 and 8 (these cells are marked with an asterisk). Under the above definition, this enables the remaining 3's in columns 3 and 8 to be excluded from the cells marked (A)

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` *--------------------------------------------------------------------* | 13     8      49     | 7      135    15     | 49     6      2      | | 136    39  (A)13469  | 13     2      8      | 459    7      59     | | 7      5      2      | 49     49     6      | 3      1      8      | |----------------------+----------------------+----------------------| | 4      139    8      | 19     6      7      | 59     2      359    | | 56     19     56     | 2      1489   3      | 7      48     49     | | 2      7     *39     | 5      489    49     | 6     *348    1      | |----------------------+----------------------+----------------------| | 135    6      7      | 134    1345   2      | 8      9      34     | | 8      4   (A)135    | 6      1359   159    | 2   (A)35     7      | | 9      2     *35     | 8      7      45     | 1     *345    6      | *--------------------------------------------------------------------*`

In addition to Pat's above guidance I hope this also helps.

Cec
Cec

Posts: 1039
Joined: 16 June 2005

For plain vanilla sudoku I think of this as "the corners of a rectangle"

The more restained ones such as X or Windoku have applications of the technique that are less visually obvious.
HATMAN

Posts: 214
Joined: 25 February 2006

What the heck. Count me in as well.

Code: Select all
`+--------------------------------------------------------------------+|  2      14     3     |  5      49     7     |  19     6      8     ||  6      5      14    |  249    2349   8     |  139    12     7     ||  8      7      9     |  12     1236   136   |  5      4      23    ||----------------------+----------------------+----------------------||  7      2      16    |  3      5      16    |  8      9      4     ||  14     9      5     |  1247   8      146   |  137    12     236   ||  3      8      146   |  1247   1246   9     |  17     5      26    ||----------------------+----------------------+----------------------||  14     6      8     |  149    1349   134   |  2      7      5     ||  5      14     7     |  8      14     2     |  6      3      9     ||  9      3      2     |  6      7      5     |  4      8      1     |+--------------------------------------------------------------------+`

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`Candidate grid for digit 4:  X-Wing r18\c25Rows 1 & 8: two candidates per row, and two common columns -- 2 & 5other candidates in columns 2 & 5 can be eliminated+-----------------------------------+|  . *4  .  |  . *4  .  |  .  .  .  ||  .  .  4  |  4 -4  .  |  .  .  .  ||  .  .  .  |  .  .  .  |  .  4  .  ||-----------+-----------+-----------||  .  .  .  |  .  .  .  |  .  .  4  ||  4  .  .  |  4  .  4  |  .  .  .  ||  .  .  4  |  4 -4  .  |  .  .  .  ||-----------+-----------+-----------||  4  .  .  |  4 -4  4  |  .  .  .  ||  . *4  .  |  . *4  .  |  .  .  .  ||  .  .  .  |  .  .  .  |  4  .  .  |+-----------------------------------+`

Code: Select all
`Candidate grid for digit 4:  X-Wing c16\r57Columns 1 & 6: two candidates per column, and two common rows -- 5 & 7other candidates in rows 5 & 7 can be eliminated+-----------------------------------+|  .  4  .  |  .  4  .  |  .  .  .  ||  .  .  4  |  4  4  .  |  .  .  .  ||  .  .  .  |  .  .  .  |  .  4  .  ||-----------+-----------+-----------||  .  .  .  |  .  .  .  |  .  .  4  || *4  .  .  | -4  . *4  |  .  .  .  ||  .  .  4  |  4  4  .  |  .  .  .  ||-----------+-----------+-----------|| *4  .  .  | -4 -4 *4  |  .  .  .  ||  .  4  .  |  .  4  .  |  .  .  .  ||  .  .  .  |  .  .  .  |  4  .  .  |+-----------------------------------+`
daj95376
2014 Supporter

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