- Hyper Sudoku adds 4 shaded 3×3 regions inside the grid — each must also contain 1–9
- These extra regions overlap with the standard boxes, creating much stronger constraints
- Window Sudoku uses a similar concept but with the inner regions arranged differently
- Extra regions mean each cell may belong to 4 units instead of 3 — more eliminations per placement
- These variants can often be solved with fewer givens than standard Sudoku
Hyper Sudoku Rules
Hyper Sudoku (also called Extra-Region Sudoku or NRC Sudoku in some markets) uses all the standard 9×9 Sudoku rules plus four additional 3×3 regions. These four extra regions are positioned at:
- Rows 2–4, Columns 2–4 (top-left inner region)
- Rows 2–4, Columns 6–8 (top-right inner region)
- Rows 6–8, Columns 2–4 (bottom-left inner region)
- Rows 6–8, Columns 6–8 (bottom-right inner region)
Each of the four extra regions must contain each digit 1–9 exactly once, just like the standard boxes.
How Extra Regions Change the Solve
The cells that lie inside the extra regions now belong to four units instead of three: their standard row, column, and box — plus the extra region. This means placing a digit in one of these cells eliminates it from four groups of peers simultaneously, creating much stronger cascade effects.
As a result, Hyper Sudoku puzzles at the same "difficulty rating" are often easier to solve than standard Sudoku of the same difficulty — the extra constraints do most of the heavy lifting.
Window Sudoku
Window Sudoku is similar in concept: extra regions are added inside the standard 9×9 grid, but the specific placement of the regions differs from Hyper Sudoku. The most common Window arrangement places the extra regions in the "gaps" between the standard boxes — the cells at positions R1C4–R3C6, for instance.
The solving approach is the same as Hyper Sudoku: identify which cells are in extra regions, and use those region constraints aggressively as additional units during scanning and elimination.
Tips for Beginners
When attempting Hyper or Window Sudoku, mark the extra regions clearly (shade them or outline them in a different color) before starting. Then treat them exactly like boxes during your solving process — scan for each digit in the extra region just as you would in a standard 3×3 box. The extra constraints almost always provide quick early wins. Try a standard Easy puzzle first to build fluency with the base rules.