Every Sudoku has only one possible puzzle solution, meaning every cell has only one possible value. You just need to find it!
Single elimination:
- Single row
- single column
- single section
Row:
Column:
Section:
Intersection:
- 2-way
- 3-way
Missing numbers in section.
Long-press a number - This technique is literally scanning by 3 lines(rows/columns) at the same time. You will see every occurence of a number in every section. Check vertical or horizontal groups of sections - it will give you insignts if where is the possible location of a number in a section without it. Check intersection - this gives you not 2 but 4 sections which will give you more information
Sub-group Exclusion
Exclusion is a reversed logic of elimination of opportunities a cell can have. It is an application of logic that knocks out options that at first sight looked possible. By excluding one possibility for a square may result in only one remaining placement opportunity, so the cell can be safely set to the remaining single possibility. Here's an example of the sub-group exclusion
.
A sub-group is a term used to describe three squares in a row or column that intersect a Sudoku region. Every row and column has three sub-groups in the three regions it crosses.
In the image above - 1's can be technically placed in any of the 4 empty cell, however if you check the highlighted horizontal row - you will notice - that any of the other empty row cell can be 1's due to intersectio. resulting in 1's can be placed only in the lower 2 cells, meaning upper 2 cells cannot carry 1's
Naked Pair - sudoku solving strategy
Have a look: The picture below shows a sudoku puzzle block with many unsolved cells. Take a closer look, we can see that bottom left and right cells can both be 6 & 9, moreover - these are only cells which can be 6 or nine.
Right, you got that! These two cells must be 6 & 9. At the current moment it doesn't really matter, which if these 2 cells is 6 and which is 9, you can remove all the other pencil marks, and greatly reduce possible placements for 8's or 7's
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