Sudoku Dark

Sudoku Dark is a logic-based, combinatorial number-placement puzzle.

Sudoku Dark is a puzzle in which missing numbers are to be filled into a 6 by 6 or 9 by 9 or 12 by 12 grid of squares which are subdivided into 3 by 3 boxes so that every row, every column, and every box contains the numbers 1 through 9.