Samurai Sudoku – Easy

Samurai Sudoku

Samurai Sudoku is a multi Sudoku puzzle. This means: The puzzle is not made up of a single classic Sudoku, but of several interconnected 9x9 Sudokus. Each sub-Sudoku follows the normal Sudoku rules: In each row, each column, and each 3x3 block, the numbers 1 to 9 must appear exactly once.

Samurai Sudoku is one of the most well-known forms of multi Sudoku. Four classic 9x9 Sudokus are located at the corners, with a fifth Sudoku in the middle. The corner Sudokus overlap with the central Sudoku.

In Samurai Sudoku, you should regularly and alternately check the four corner areas and the center. The center connects the otherwise separate corners. As with all Sudokus, no arithmetic calculations are involved. The numbers are symbols that are placed correctly through logical elimination.

Basic Rules

• The puzzle consists of several classic 9x9 Sudokus connected into a common figure.
• Exactly one number from 1 to 9 is entered in each active cell.
• Within each individual 9x9 Sudoku, each row must contain the numbers 1 to 9 exactly once.
• Within each individual 9x9 Sudoku, each column must contain the numbers 1 to 9 exactly once.
• Within each individual 9x9 Sudoku, each 3x3 block must contain the numbers 1 to 9 exactly once.
• Shared cells belong to multiple sub-Sudokus simultaneously. The value entered there is the same for all involved sub-Sudokus.
• Given numbers may not be changed.
• Empty areas outside the visible grid are not part of the puzzle and are not filled in.
• A multi Sudoku is solved when each contained 9x9 Sudoku is correctly solved and all shared cells match.
• Important: A long visible row is not automatically a Sudoku row. The boundaries of the respective 9x9 sub-Sudoku always determine the relevant rows.

Strategies for Solving

The basic techniques correspond to those of classic Sudoku. The difference is that certain definite entries in one sub-Sudoku can influence others, especially shared cells and overlapping areas.

1. Check a single sub-Sudoku like a normal Sudoku

Start with a sub-Sudoku that already has many numbers placed. Often, simple definite entries can be found here without analyzing the entire multi Sudoku at once.

In the considered 9x9 sub-Sudoku, one row is 43172689. The numbers 1, 2, 3, 4, 6, 7, 8, and 9 are already present. The only missing number is 5. Therefore, the last open cell in this sub-Sudoku row must be a 5.

This conclusion applies only to the nine cells of this one sub-Sudoku row, not the entire visible width of the figure.

2. Hidden single candidate in a 3x3 block

Not every safe number arises from an almost complete row. Often, a number can only fit in one place within a 3x3 block. In the following complete Samurai Sudoku grid, we examine the top-left 3x3 block of a sub-Sudoku to find the number 5.

In the considered sub-Sudoku, the 5 is checked within the top-left 3x3 block. The second and third rows of this sub-Sudoku already contain a 5, so the 5 cannot be in those two rows in this block. Additionally, the first and second columns of this sub-Sudoku already contain a 5. Consequently, the first two cells of the first row of the block are eliminated, leaving only the third cell in that row as an option. This cell must hold the 5.

This is a hidden single candidate. It may not seem obvious at first, but for the number 5, this is the only permissible position in the examined block.

3. Use a shared cell as a bridge

Shared cells are the most important feature of Samurai Sudoku. A shared cell belongs to multiple sub-Sudokus. When a number is securely determined there, it must be immediately considered in all involved sub-Sudokus.

In the first 9-row of the example, the sequence 276314.89 is present. Within this sub-Sudoku, only the 5 is missing. The open cell is also part of the adjacent sub-Sudoku. Once the 5 is placed, it also changes the 9 in the corresponding 9-row there.

This first entry is not just a local progress; it is also an indication for the neighboring sub-Sudoku, because the same cell is part of a row, a column, and a 3x3 block in that sub-Sudoku as well.

4. Develop a follow-up step from an overlapping

In the adjacent sub-Sudoku, the relevant 9-row is 58912346. Only the 7 is missing there, so that cell can also be securely filled.

This example illustrates the typical multi Sudoku effect: first, a cell in one sub-Sudoku is safely solved. Because this cell is shared, a further secure step immediately arises in the neighboring sub-Sudoku.

5. Carefully check candidates in overlaps

A normal Sudoku cell is limited by a row, a column, and a 3x3 block. A shared cell can also belong to other rows, columns, and blocks in different sub-Sudokus. Therefore, a candidate in a shared cell can only remain if it is allowed in all involved sub-Sudokus.

Practically, this means: do not only check a shared cell from the perspective of the current sub-Sudoku. Switch consciously to the other sub-Sudoku and verify the row, column, and block there as well. This often makes shared cells identifiable as edge or outer cells earlier.

6. Carefully track the boundaries of sub-Sudokus

Samurai Sudoku looks like a large connected puzzle. Still, the logic arises from the individual 9x9 Sudokus. A visible row may contain parts of different sub-Sudoku rows. Therefore, it is important to always clearly note which 9x9 Sudoku is currently being considered.

Typical solving process

1. Get an overview of the arrangement: four corner Sudokus and a central 9x9 Sudoku.
2. Select a sub-Sudoku with many given clues and look for safe classical Sudoku steps there.
3. Check nearly complete rows, columns, and 3x3 blocks.
4. Search for hidden single candidates: numbers that can only fit in one position within a region.
5. Mentally mark shared cells and overlapping areas.
6. Immediately transfer each safe entry in a shared cell to all involved sub-Sudokus.
7. Then, check whether new single candidates or eliminations arise in neighboring sub-Sudokus.
8. Regularly switch between the sub-Sudokus instead of solving in one area in isolation.
9. At each entry, verify its legality in all affected rows, columns, and 3x3 blocks.
10. Finish the puzzle only when all individual 9x9 Sudokus are fully and consistently solved.

Common mistakes

• Treat the entire figure as one big Sudoku. The rules only apply within the individual 9x9 Sudokus.
• Update shared cells in just one sub-Sudoku. A shared cell affects all sub-Sudokus it belongs to.
• Misinterpret boundaries. Not every visible row is part of the same Sudoku row on offset grids.
• Interpret regions without grids as cells. Empty areas outside the grid are not filled in.
• Rely on guesswork too early. A wrong entry can damage multiple sub-Sudokus simultaneously.
• Fail to check candidates in overlaps rigorously enough. A candidate must be permissible in all affected rows, columns, and blocks in all involved sub-Sudokus.
• Do not continue checking after a secure entry. Shared cells often produce immediate new eliminations.

Tips for beginners

• Start with a single sub-Sudoku and solve only safe steps there.
• Early on, identify shared areas. These often create the most important connections.
• Strictly observe the 9x9 boundaries of each Sudoku.
• Always check all involved sub-Sudokus for shared cells, not just the current area.
• Use candidate notes once multiple sub-Sudokus are in play.
• Switch perspective: If a sub-Sudoku stalls, check the neighboring shared cells.
• Ask yourself for each entry: In which sub-Sudoku is this number certain, and does it also influence another sub-Sudoku?
• View overlaps not just as difficulty, but as additional hints.

Samurai Sudoku extends the classical Sudoku without changing its fundamental logic. Each number still follows the known Sudoku rules. The challenge is to seamlessly connect multiple sub-Sudokus. If you use the shared cells consistently, you can solve complex multi Sudoku puzzles step by step with logical reasoning.