Windoku - also widely known as Hyper Sudoku or NRC Sudoku - adds four extra 3x3 shaded regions to the classic 9x9 grid. Each of these "windows" must contain the digits 1 through 9 exactly once, layering additional constraints on top of the standard Sudoku rules. The result is a visually distinctive variant that sharpens your elimination skills and offers a fresh perspective on familiar puzzle logic.
Windoku uses the standard 9x9 Sudoku grid and follows all the classic Sudoku rules - each row, column, and 3x3 box must contain digits 1 through 9 exactly once. What makes Windoku unique is the addition of four extra 3x3 regions, typically highlighted with shading or a background color, that must also individually contain all nine digits.
These four regions are positioned symmetrically within the grid, offset from the standard boxes. They occupy the following positions: rows 2 to 4 and columns 2 to 4 (top-left window), rows 2 to 4 and columns 6 to 8 (top-right window), rows 6 to 8 and columns 2 to 4 (bottom-left window), and rows 6 to 8 and columns 6 to 8 (bottom-right window). Together, these windows create a distinctive visual pattern that gives the puzzle its name.
The name "Windoku" derives from "window" and "Sudoku," referring to the four window-like regions. In some regions, particularly Europe, the variant is called Hyper Sudoku. The Dutch newspaper NRC Handelsblad was among the first major publications to feature this variant regularly, leading to the alternate name "NRC Sudoku" in the Netherlands and surrounding countries.
Windoku follows all standard Sudoku rules, plus one additional constraint:
Each of the four shaded 3x3 windows must contain the digits 1 through 9 exactly once. The four windows are fixed in position: they are always in the same locations on the grid (rows 2-4/columns 2-4, rows 2-4/columns 6-8, rows 6-8/columns 2-4, rows 6-8/columns 6-8). Standard row, column, and 3x3 box rules still apply simultaneously. Many cells belong to both a standard 3x3 box and a window, creating powerful intersection constraints.
An interesting consequence of the window positions is that they also implicitly constrain the remaining cells. The cells that are not in any window form their own patterns, and experienced solvers learn to recognize how window placements interact with standard box constraints to create additional deduction opportunities.
Windoku is rated as intermediate difficulty. Interestingly, the extra window constraints often make puzzles somewhat easier to solve than a comparably rated classic Sudoku. The windows provide additional regions where digits cannot repeat, giving solvers more tools for elimination and candidate narrowing.
This variant is perfect for solvers who are comfortable with basic Sudoku and want a gentle introduction to variant puzzles. If you have mastered classic Sudoku and want to try something new without a steep learning curve, Windoku is an excellent choice. The rules are easy to understand, and the additional constraints often lead to satisfying "chain reaction" deductions where placing one digit unlocks several others.
Always remember to check the window constraints alongside the standard box constraints. When you place a digit in a cell that belongs to both a box and a window, that digit is eliminated from both regions simultaneously. This dual elimination is the key advantage Windoku gives you and is the foundation of most window-specific deductions.
Look for cells that sit at the intersection of a row, column, box, and window. These cells are constrained by four different regions, making them excellent candidates for early resolution. If three of those four regions already have a particular digit placed, the cell cannot contain that digit - even if it seems possible from just one perspective.
Apply standard Sudoku strategies like naked singles, hidden singles, and pointing pairs to both the standard boxes and the windows. Techniques like box-line reduction work within windows just as they do within standard boxes. As you practice, you will develop an intuition for how window constraints interact with standard constraints, and your solving speed will increase significantly.
Windoku has been a popular Sudoku variant since the mid-2000s when the global Sudoku boom created demand for interesting variations on the classic format. The Dutch newspaper NRC Handelsblad was one of the first major publications to regularly feature the variant, publishing it under the name "NRC Sudoku." This early exposure helped establish the variant in European puzzle culture.
The variant is featured in international puzzle competitions and is widely available on online puzzle platforms and in puzzle books. Its visual appeal - the four shaded windows create an immediately recognizable and attractive grid pattern - has made it a favorite among puzzle publishers. Windoku continues to be one of the most accessible and popular Sudoku variants worldwide, bridging the gap between classic Sudoku and more complex constraint-based variants.
Windoku, also known as Hyper Sudoku or NRC Sudoku, is a Sudoku variant that adds four extra 3x3 shaded regions (windows) to the standard 9x9 grid. Each of these four windows must also contain the digits 1 through 9 without repetition, in addition to the standard row, column, and box constraints.
Windoku and Hyper Sudoku are the same puzzle - just different names used in different regions. The name 'Windoku' comes from the four 'windows' overlaid on the grid, while 'Hyper Sudoku' emphasizes the additional constraints beyond standard Sudoku. Some publications also call it NRC Sudoku, after the Dutch newspaper NRC Handelsblad that popularized it.
The four windows are positioned symmetrically within the grid. They occupy cells at rows 2-4/columns 2-4, rows 2-4/columns 6-8, rows 6-8/columns 2-4, and rows 6-8/columns 6-8. Visually, they appear as four shaded 3x3 blocks that are offset from the standard 3x3 boxes, creating a pattern that somewhat resembles a window frame.
Windoku is generally considered intermediate difficulty. Surprisingly, the extra constraints often make Windoku puzzles easier to solve than standard Sudoku of similar ratings. The four additional windows provide more elimination opportunities, which means solvers can resolve cells faster. However, keeping track of which window a cell belongs to adds a layer of mental bookkeeping.
The key strategy is to always check the window constraints in addition to the standard row, column, and box checks. When you place or eliminate a digit, consider its impact on any window it belongs to. Many cells belong to both a standard box and a window, creating powerful intersection constraints. Standard techniques like naked singles, hidden singles, and pointing pairs all apply, but you should check them across windows as well as boxes.
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