Logic Masters Deutschland e.V.

Fans of Cracking the Cryptic already know the secret of sudoku, which Simon only shares with his very favourite people. (I won't reveal it here, in case someone not on Simon's list is reading this.) That secret applies to all sudoku puzzles, including this one. But this puzzle also has 2 other secrets, described below.

Standard sudoku rules apply: Fill the grid with digits from 1 to 9 so that each digit occurs exactly once in each row, column, and 3x3 box.

Standard yin-yang rules apply: Shade some cells in the grid so that the shaded cells form an orthogonally connected region, the unshaded cells form an orthogonally connected region, and no 2x2 square is completely shaded or completely unshaded.

Circles and squares: A cell with a circle is shaded, and its digit counts the number of shaded cells visible horizontally or vertically from the cell, where unshaded cells block vision. A cell with a square is unshaded, and its digit counts the number of unshaded cells visible horizontally or vertically from the cell, where shaded cells block vision. In both cases, the cell itself is included in the count. All possible circles and squares are shown. (See example below.)

Dark secrets: There are numbers R and C, to be discovered by the solver, such that: In every row with at least one shaded cell, the sum of the shaded digits is R. In every column with at least one shaded cell, the sum of the shaded digits is C.

You can solve this in SudokuPad.

This example illustrates the circles and squares rule (but with no dark secrets):