Sudoku Assistant - The Sudoku Trainer and Solver

Block Interaction

On occasion, we need to consider the possible locations for a value across a whole column or row of subgrids, and the columns (or rows) within those subgrids.

The example should help clarify this. We are looking specifically at the possible locations for value 5, in the central column of subgrids. The lower two subgrids show the 'activating' groupings of cells highlighted in green... let's call these candidate columns. The possible locations in these two subgrids are all in the same two candidate columns. Look at it this way, if the 5 is in column 4 of subgrid 5, then it will have to be in column 6 in subgrid 8 (and vice versa)... so whichever way, the cells highlighted in red in the third subgrid can not be 5, so can have that value removed from the list of pencil-marks / candidate cells.

      5 5 5      
      5 5 5      
      5 5 5      
      5 4 5      
  5              
      5 3 5      
      5 6 5      
      5 1 5      
      5 2 5      

The subgrids with matching candidate rows or columns do not have to be adjacent... and as usual, it doesn't matter how or why you get the candidate columns or rows that match-up!

If you are unsure of any of the terminology we use, you may find it helpful to refer to our Glossary.

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