Asterisk Sudoku – Hard

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Asterisk Sudoku is a variant of the classic Sudoku, a number placement puzzle traditionally presented in a 9x9 grid, subdivided into 3x3 subgrids or "regions." The grid partially fills with numbers, referred to as "givens." The objective is to populate the empty cells in such a way that each number 1 through 9 appears exactly once in each row, column, and region. In the Asterisk Sudoku variant, an additional constraint is introduced with a specially shaded area, an "asterisk," which must also contain the numbers 1 through 9 without repetition.

Basic Rules

1. Grid Structure: The puzzle consists of a 9x9 grid, and this grid is further divided into 3x3 subgrids/regions.
2. Givens: Some cells are pre-filled with numbers, known as "givens."
3. Number Placement: The player must fill the empty cells with numbers 1 through 9.

Additional Rules for Asterisk Sudoku

4. Asterisk Region: There is an additional, specially shaded area (forming an asterisk shape) in the grid.
5. Unique Asterisk Numbers: The numbers 1 through 9 must appear without repetition in the shaded asterisk area, in addition to the standard Sudoku rules.

Basic Solving Tips

• Single Possibility: If a cell is the only one in its row, column, or region that can contain a particular number, that number must go in that cell.
• Elimination: Determine what numbers cannot be in a cell to figure out what number can be.
• Double Pairs: If two cells in a row, column, or region can only be two numbers (like 3 and 6), then eliminate these two numbers from the other cells in that section.
• Look for Grid Symmetry: Often, the given numbers (and therefore the solution) have a symmetrical arrangement. This might help to focus on certain areas of the grid.
• Asterisk Focus: Pay special attention to the asterisk area and use it to your advantage to eliminate possibilities in other regions, rows, and columns