Hello,
I submit a method I use in my solver. I don't know if it has already been described.
If that is the case, thank you to indicate me, and sorry for describing a known algorithm.
I call this method "Rank X-wing" or "RXW". At first, 2 definitions :
Rank : group of consecutives lines associated to boxes (there are 3 ranks on a 9x9 sudoku : lines 123, 456 and 789).
Segment : intersection between a line and a box.
The RXW definition is : "Inside a rank, if candidate K is present at least 2 times on Ns segments S1-S2…SNs located on N lines L1-L2…LN and on N boxes B1-B2…BN, and if K is not present on the other segments of L1-L2…LN, then K can be removed in B1-B2…BN except in segments S1-S2…SNs".
Of course, same definition by changing line by column.
RXW is of little interest for 9x9 grids because RXW is here equivalent to "line-box interaction", but I have developed a site http://sudokugeant.cabanova.com based on large grids (up to 100x100) and RXW can be efficient on grids over 9x9, as the probability to get an RXW increases with the grid size, the number of ranks and lines by rank.
If you are interested, I can add details.
Thanks for your comments,
Phil
