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How to play samurai sudoku
Picture four ordinary sudoku grids in the corners and a fifth one in the middle, overlapping each of them by one 3 by 3 box. Altogether the board is 21 squares wide and 21 tall, with 369 squares to fill.
- Each of the five grids follows the normal rules: every row, column and 3 by 3 box in that grid holds 1 to 9 exactly once.
- The four shaded boxes belong to two grids at the same time, so the digits in them have to work for both.
- Rows and columns stop at the edge of their own grid. A row in the top-left grid does not carry on into the top-right grid.
A small example of how the overlap helps: say a shared box has a 6 in its top row. That 6 rules out 6 for the rest of that row in the corner grid, and also for the rest of the same row in the centre grid. One digit gives you information in two grids at once.
Using the board
Whole board shows all five grids. On a small screen, press Zoom in and scroll inside the board to move around. One grid shows a single 9 by 9 grid at a comfortable size, with its shared boxes shaded; pick which grid with the little map of five squares. Your entries carry across both views, since they are the same board.
Notes, undo, erase, check and hints work as they do on our other sudoku games, and your progress is saved on your device. Print gives you a clean black-and-white copy of the board, including anything you have filled in so far.
Medium puzzles need nothing beyond singles. Hard puzzles also call for pairs and pointing. Both come with a new daily grid, and New puzzle makes another whenever you want one.
Samurai sudoku strategy
Start in the shared corner boxes
The shared boxes get pressure from two grids, which makes them the easiest places to place digits early. Scan each one against the rows and columns of both grids that pass through it. A digit that is blocked in the corner grid may be blocked in a different way in the centre grid, and together the two can leave just one spot.
Find the friendliest grid
The clues are rarely spread evenly. Look for the grid with the most numbers in it, often a corner grid, and push it as far as you can. Every digit you place in its shared box feeds straight into the centre grid.
Work the centre last, but check it often
The centre grid touches all four shared boxes, so it usually can't be cracked on its own at the start. Come back to it each time you finish a shared box. Very often a centre row that looked hopeless will have two or three digits by then.
Use notes on the overlaps
When a shared box stalls, pencil in its candidates. Pairs and pointing inside a shared box remove candidates in both grids at once, which is exactly what the Hard level is built around.
Keep track of where you are
With 369 squares, it is easy to lose your place. Finishing one grid fully before moving on helps, and the counters on the number pad show how many of each digit are still to be placed across the whole board (41 of each in total).
More sudoku to play
For a single grid with a sharper bite, try evil sudoku. Killer sudoku replaces the clues with cage sums, and the printable sudoku maker builds whole sheets of puzzles for the kitchen table. If you would rather play with pictures, Canoku is our Canadian emoji sudoku.