## DS: Disjoint SubsetsLook in a row, column or box if there are x number of cells containing x possible numbers, where all the cells has the same possible numbers. Meaning, if a cell has only 2 and 3 as possible numbers, look for another cell in the same row, column or box which also has only 2 and 3 as possible numbers. If this exists, these cells must contain the number 2 or 3 as solution and we can remove 2 and 3 from the row, column or box.
Here you see that R3 has two cells which have 3 and 5 as possible solutions. Therefore we can remove 3 and 5 from the other cells in R3, in this case 3 and 5 from R3C4 and 3 from R3C5.
This doesn't work only for 2 numbers in 2 cells. You can do it for the same numbers in 3 cells, 4 cells etc. This sudoku can be solved using DS and SiSo. |