Nodoku

Nodoku is a logic puzzle that blends elements of Sudoku and nonograms. In a nodoku puzzle, solvers work on a square grid, commonly 9 by 9, though other sizes are used. The Sudoku aspect requires that digits 1 through 9 appear exactly once in every row and in every column, and, when the grid is subdivided, within each 3×3 block as well. The Nonogram aspect provides shading clues: for each row and column, a sequence of numbers indicates the lengths of consecutive shaded runs. In the solution, the shaded cells must form a pattern that matches all row and column clues.

Typically, digits may be placed only in shaded cells, while unshaded cells remain empty. Some puzzles provide a few digits or a few shaded cells to seed the solving process. The challenge is to satisfy both the Sudoku constraints and the Nonogram shading simultaneously, which often requires combining techniques from both puzzle types, such as candidate elimination, naked and hidden pairs, and line-by-line shading deductions.

Variants of nodoku exist that change grid size, use alternative block structures, or relax certain constraints (for example, allowing digits to appear more than once in a row if not in the same shading block). The puzzles can emphasize aesthetic outcomes, producing recognizable pictures when the final shading is revealed.

See also: Sudoku, Nonogram, Puzzle hybrid.