Sudoku DG has 9 additional groups.

(Group = set of cells that has to contain 1-9. In ordinary sudoku a group means a row or column or box. Sudoku X has 2 additional groups, the 2 diagonals.)

The 9 additional groups are the cells in the same position within each 3x3 box. For example, these cells

- Code: Select all
`. x . | . x . | . x .`

. . . | . . . | . . .

. . . | . . . | . . .

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. x . | . x . | . x .

. . . | . . . | . . .

. . . | . . . | . . .

---------------------

. x . | . x . | . x .

. . . | . . . | . . .

. . . | . . . | . . .

are one additional group. There is one additional group for each position. In Sudoku DG, each of these 9 additional groups has to contain 1-9.

Question: What is the minimum number of clues for a sudoku DG puzzle?

Here is a puzzle with 13 clues.

000000000000006003000900002000000000020000800000000070000000006900180500000050000

- Code: Select all
`. . . | . . . | . . .`

. . . | . . 6 | . . 3

. . . | 9 . . | . . 2

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. . . | . . . | . . .

. 2 . | . . . | 8 . .

. . . | . . . | . 7 .

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. . . | . . . | . . 6

9 . . | 1 8 . | 5 . .

. . . | . 5 . | . . .

This was found using checker. Presumably the people with random search programs can do better....is there a 12?

Can anyone tell me if this is a hard puzzle?