Twodoku – Medium

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Twodoku, also sometimes referred to as "Double Sudoku," is a variant of the classic Sudoku puzzle. It involves two separate 9x9 grids that need to be solved simultaneously while adhering to the standard Sudoku rules. The challenge comes from the necessity to ensure that the solutions are valid for both grids.

Basic Rules

1. Grid Structure: Each Twodoku puzzle consists of two 9x9 grids.
2. Number Placement: Numbers 1 through 9 must be placed in each row, column, and 3x3 subgrid.
3. No Repetition: No number can be repeated in any row, column, or 3x3 subgrid within each 9x9 grid.

Additional Rules

• Interconnected Solutions: The solution to one grid often impacts the solution to the other. Some cells in one grid may be influenced by the corresponding cells in the other grid.

Basic Solving Tips

• Start with Certainties: Begin by filling in numbers that are certain and have only one possible place in a row, column, or subgrid.
• Look for Grid Intersections: Pay attention to how the two grids intersect and influence each other. A number in one grid may determine the placement of a number in the corresponding position in the other grid.
• Use Pencil Marks: Utilize pencil marks to keep track of possible numbers for a cell, eliminating options as you progress.
• Work on Both Grids Simultaneously: Don’t try to complete one grid first; work on both grids in tandem to utilize clues from each grid to solve the other.