What is the best sudoku strategy

Sudoku - solution strategies

The basic strategies for solving a Sudoku are Naked single and Hidden single. Easy Sudokus usually only require knowledge of these two rules. All other strategies often only serve to reduce the number of possible values ​​in the individual boxes and then again both strategies Naked single and Hidden single apply.

1. Naked Single - unique value

Naked single means that a box can only take on this one value. All other values ​​for this box are impossible because they are already taken.

This rule gives an immediate result!

The red point can only value 1 assume, since all other values ​​are already taken. The values ​​9, 8, 7 are assigned in the column. The values ​​6, 3, 5 are assigned in the line and the values ​​7, 4, 2, 3 are assigned in the block. Therefore, the box can no longer assume the following values: 2, 3, 4, 5, 6, 7, 8, 9. This means that the only possible value is the 1 (Naked single).

2. Hidden single - only possible place

The box must assume this value, as all other boxes cannot accept this value.

This rule gives an immediate result!

In the block at the top left the value 1 be awarded. Since in columns A and C the value 1 is forgiven, the value must 1 occur in the block at the top left in column B. Since rows 1 and 3 are already assigned in column B of this block, the box is 2 B the only possible place (Hidden single).

3. Naked Subset - there is a distinct subset

If three boxes within one area can only assume three identical values, then these values ​​can be crossed out in the other boxes within this area. If there are three values, one speaks of a naked triple. The same goes for two, four, five values, etc.

Only the area below center is considered. The small digits are the possible values ​​in the individual boxes. Only the values ​​1, 2, 3 can appear in boxes D7, F7 and F9. All other values ​​for these three boxes were discarded through a process of elimination. Therefore we can delete the values ​​1, 2, 3 in all other boxes in this area (red digits). Also applies to two, four values, etc. (Naked subset).

4. Hidden subset - there are unique locations

If two values ​​can only appear in two boxes, then these two boxes must assume these values. In all other boxes these values ​​can be deleted (hidden pair). Which of these two boxes has which value cannot yet be determined.

Only the area below center is considered. The cheeses F7 and F9 can only the values 1 and 2 accept. Hence the values 1 and 2 in all other boxes in this area should be deleted.

5. Dependency on row or column and block

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6. Dependency on two blocks

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7. Forcing Chains

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8. Crosswing or X-Wing

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9. Swordfish

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