Sudoku Single Position

There are 2 fundamental techniques you need to be able to use to start solving Sudoku grids, Single Position and Single Candidate.

Let's have a look at Single Position!

We know that we need to insert the numbers 1 -> 9 in every row.

We are missing the numbers 2, 4 and 7 from the second row - we know they must appear somewhere in that row, but we don't know where.

We can insert the number 2 in cells B or C. Can you see why?

We can only insert the number 4 in cell A, i.e. the Single Position for 4 in this row is cell A, we can insert 4 in cell A.

We can insert the number 7 in cells A, B or C.

The Single Position technique allows us to insert 4 in cell A, but we can't insert 2 or 7 yet.

This is the same idea, but looking at a column instead.

The second column here is missing the numbers 2, 4, 5, 6, 7, and 9.

We can't decide anything about 2, 4, 5, 6 or 9 right now, but the 7 can only be inserted in the cell labelled A.

Again, same idea, but looking at the region instead.

The bottom-left region is missing the numbers 1, 2, 3, 4, 5, 6, and 9.

We can't decide anything about 1, 2, 4, 5, 6 or 9 right now, but the 3 can only be inserted in the cell labelled A.

We are missing the number 5 from the highlighted region, can you spot which cell it should go in?

It can only be inserted in the middle cell.

Putting the number 5 in any other cell in this region would break the rules of Sudoku, i.e. you can't insert the same number twice in the same region (or row or column).

We are missing the number 8 from the highlighted column, can you spot which cell it should go in?

It can only be inserted in the top cell.

Putting the number 8 in any other cell in this region would break the rules of Sudoku, i.e. you can't insert the same number twice in the same region (or row or column).

We are missing several numbers in the highlighted row, but we can insert one of them using Single Position, can you find this missing number?

Did you spot the number 2 we can insert in this row?

That's everything you need to know about the Single Position technique.

You can apply the Single Position technique to a row, column or region - the underlying principle is the same each time.

The best place to look for Single Position numbers is rows/column/regions that are almost filled - they're easier to spot and they're more likely to have Single Position values.

Sudoku Academy

Single Position

Sudoku Single Position

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