Samurai sudoku rules
Five grids, four shared boxes, one solution. Here is how it works.
What is samurai sudoku?
Samurai sudoku is five standard 9×9 sudoku grids arranged in an X pattern. There is one grid in each corner — top-left, top-right, bottom-left, bottom-right — and one in the center. The overall layout is 21 rows by 21 columns.
The grids are not independent. Four 3×3 boxes are shared between the center grid and the corner grids. The bottom-right box of the top-left grid is the same physical cells as the top-left box of the center grid. The same applies to all four corners. This overlap is what makes samurai sudoku different from solving five separate puzzles.
The rules
- Standard sudoku rules apply to each grid. Every row, column, and 3×3 box within each of the five 9×9 grids must contain the digits 1 through 9 exactly once.
- Shared boxes obey both grids. Cells in a shared 3×3 box must satisfy the row, column, and box constraints from both parent grids simultaneously.
- Dead zones are not playable. The four rectangular gaps in the 21×21 layout (between corner and center grids) contain no cells. Ignore them.
That is the complete ruleset. If you know sudoku, you already know 90% of samurai sudoku. The new element is thinking across grids through shared boxes.
How shared boxes work
The four shared boxes connect the layout:
- Top-left ↔ Center: The bottom-right box of the TL grid is the top-left box of the center grid.
- Top-right ↔ Center: The bottom-left box of the TR grid is the top-right box of the center grid.
- Bottom-left ↔ Center: The top-right box of the BL grid is the bottom-left box of the center grid.
- Bottom-right ↔ Center: The top-left box of the BR grid is the bottom-right box of the center grid.
When you place a digit in a shared box, it eliminates that digit from the corresponding row, column, and box in both grids. This dual elimination is the primary source of cross-grid deductions.
Solving strategy
The general approach:
- Start with the center grid. It shares a box with all four corner grids, making it the most constrained. Progress there ripples outward.
- Solve shared boxes early. Each digit you place in a shared box gives information to two grids at once. Prioritize these cells.
- Bounce between grids. When you get stuck in one grid, switch to a grid that shares a box with it. New placements there may unlock the stuck area.
- Use pencil marks liberally. With five grids and 405 cells, keeping track of candidates in your head is impractical. Mark candidates in every uncertain cell.
- Check cross-grid consistency. After placing a digit in a shared box, immediately check whether it eliminates candidates in the other parent grid. This is where most breakthroughs happen.
Difficulty levels
| Level | Total givens | Cross-grid logic |
|---|---|---|
| Easy | 160–200 | Minimal — most grids solvable independently |
| Medium | 120–159 | Basic cross-grid singles needed |
| Hard | 80–119 | Regular cross-grid deduction required |
| Expert | 50–79 | Heavy cross-grid chains, hidden pairs |
| Einstein | 30–49 | Logic-only certified, advanced cross-grid |
All puzzles are verified to have exactly one solution and are solvable through logic alone — no guessing at any level.
How to play on this site
Click or tap a cell to select it. Type a digit (1-9) or use the number pad. On mobile, use Focus Mode to zoom into one grid at a time — tap the TL, TR, C, BL, or BR buttons to switch between grids.
Shared cells appear with a subtle tint. When you place a digit in a shared cell, it automatically fills the same cell in the other parent grid. Conflicts are highlighted in red across both grids.
Arrow keys navigate within and across grids, skipping dead zones. Press N to toggle pencil marks. Press H for a hint. Ctrl+Z to undo.
Frequently asked questions
What is samurai sudoku?
Five overlapping 9×9 sudoku grids arranged in an X pattern on a 21×21 layout. Four 3×3 boxes are shared between corner grids and the center grid. All five grids must be solved simultaneously.
How many grids are in samurai sudoku?
Five: top-left, top-right, center, bottom-left, and bottom-right. They share four 3×3 boxes through the center.
Is samurai sudoku harder than regular sudoku?
It is larger and takes longer, but the shared boxes provide extra constraints that can actually make deductions easier. Easy samurai puzzles can be simpler to reason about than hard standard sudoku. Difficulty depends on the number of givens and cross-grid techniques required.
How do shared boxes work?
Each shared box belongs to two grids. A digit placed there must satisfy rows, columns, and boxes from both grids. This dual constraint is what makes cross-grid deduction possible and necessary.
What are the dead zones?
Dead zones are the four empty rectangular areas between the corner grids in the 21×21 layout where no grid exists. They are not playable cells.
Can I solve each grid independently?
No. The shared boxes link all five grids. You need information from one grid to solve cells in another through the shared boxes. Working across grids is required.
Related puzzle rules
- Sudoku rules — Standard 9×9 sudoku, the foundation for samurai
- Killer Sudoku rules — Sudoku with cage sums, no given digits
- KenKen rules — Arithmetic cages on a Latin square grid
Ready to play? Start with an easy puzzle or pick your difficulty.