Butterfly Sudoku – Hard

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Butterfly Sudoku is a captivating variant of the classic Sudoku puzzle. It involves a unique layout that resembles a butterfly, consisting of four 9x9 grids, arranged in a specific pattern. The challenge is to fill each grid with numbers from 1 to 9 while adhering to the traditional Sudoku rules and some additional constraints that make the puzzle intriguing.

Basic Rules

1. Grid Structure: The puzzle consists of four 9x9 grids.
2. Number Placement: Each of the four grids must be filled with numbers 1 through 9.
3. No Repetition: A number cannot be repeated in any row, column, or designated 3x3 square within each 9x9 grid.

Additional Rules

1. Interlocking Grids: The grids are arranged in a way that they share regions with each other. The shared regions must also adhere to the rule of no repetition of numbers.

Basic Solving Tips

• Start with Given Clues: Identify and fill in the definite numbers using the given clues.
• Single Possibility: Look for squares where only one number can possibly go, considering the rules.
• Exclusion: Identify numbers that cannot go in a particular square and exclude them, narrowing down the possibilities.
• Look for Grid Intersections: Pay attention to the shared regions between the grids, as they can provide crucial clues for number placement.
• Use Pencil Marks: Make use of pencil marks to note down possible numbers in a square, which can be especially helpful in multi-grid variations like Butterfly Sudoku.