Windoku 9×9 Extreme — Set 87
Solver Notes
Windoku — Free Online & Printable
Windoku, also known as Window Sudoku or NRC Sudoku, adds four fixed 3×3 window regions to the standard 9×9 grid. The windows are positioned symmetrically: top-left at rows 2-4, columns 2-4; top-right at rows 2-4, columns 6-8; bottom-left at rows 6-8, columns 2-4; bottom-right at rows 6-8, columns 6-8. Every window must contain digits 1-9 without repetition, in addition to standard row, column, and box constraints. The overlapping nature of windows and standard boxes creates rich constraint chains that experienced solvers find deeply satisfying.
About the 9×9 Grid
The 9×9 grid is the full standard size for all sudoku variants. With 81 cells in 3×3 boxes, a 9×9 variant puzzle takes 10 to 60+ minutes depending on difficulty level and variant type. All variant rules reach their full expressive potential at this size: Killer cages create complex arithmetic networks, Jigsaw regions form visually distinctive shapes, and diagonal constraints span the entire grid. The 9×9 is where experienced solvers spend most of their time, and where the depth and elegance of each variant rule is fully revealed.
Extreme Difficulty
Extreme difficulty represents the hardest puzzles solvable through pure logic — no guessing required, but the reasoning chains are exceptionally long. Required techniques include forcing chains (sequences of implications that eliminate candidates by showing they lead to contradictions), multi-step coloring, and in some cases trial-and-error with backtracking when chains become impractical to track mentally. These puzzles are designed for experienced competitors and dedicated enthusiasts. Average time: 60+ minutes. Even experienced solvers may spend 10-15 minutes without making a single cell entry while planning a deduction chain.
How to Get Started
- Choose "New Puzzle" to generate a fresh Windoku puzzle with a unique solution
- Click or tap cells to enter numbers (1–9)
- Use the constraint highlights to track which numbers are still available
- Print the puzzle if you prefer solving on paper