Samurai Sudoku Solver
Five 9×9 sudoku grids overlapping in a plus shape — the center grid shares its four corner boxes with the four outer grids. Each of the five grids must be a valid sudoku.
About Samurai Sudoku
Samurai Sudoku (also called Gattai-5) is a composite puzzle made of five overlapping 9×9 sudoku grids arranged in a plus shape on a 21×21 board. Four corner grids sit at the top-left, top-right, bottom-left, and bottom-right, and a fifth central grid overlaps each of them by sharing one 3×3 box.
Each of the five sub-grids must satisfy the standard sudoku rules independently: every row, column, and 3×3 box must contain the digits 1–9 with no repeats. Because the four shared boxes constrain two grids at once, samurai puzzles require careful cross-grid reasoning. Our solver uses backtracking with a most-constrained-cell heuristic so that even hard puzzles solve in milliseconds.
Frequently Asked Questions
What is Samurai Sudoku?
Samurai Sudoku is a variant made of five overlapping 9×9 sudoku grids forming a plus shape. The center grid shares one 3×3 box with each of the four corner grids.
How big is the board?
The board is 21×21 cells, but only the cells belonging to one of the five 9×9 sub-grids are active. The four corner regions outside the plus shape are blank.
Do the same sudoku rules apply?
Yes. Each of the five sub-grids must contain digits 1–9 in every row, column, and 3×3 box, with no repeats. The four shared boxes belong to two grids at once.
Can I enter my own puzzle?
Yes — click Reset to clear the board, type your clues into any cells, then press Solve Instant to compute the unique solution.