Best SudokuAnti-King
Anti-King Sudoku adds a chess rule to classic Sudoku: two cells that touch, even diagonally, can’t hold the same digit. A chess king moves one cell in any direction, so every digit is fenced off from all eight cells around it.
The rules
- Fill the grid so every row, column and 3×3 box holds 1 to 9.
- Cells that touch, including diagonally, can’t hold the same number.
An example puzzle
An Easy Anti-King puzzle with 20 starting digits. It has one solution.
Solving tips
- Rows and columns already stop equal digits touching side by side. The new part is the diagonals, so focus on the four diagonal neighbours of each digit.
- Two cells that touch diagonally inside one box were already in the same box, so the new rule matters most for cells in different boxes that touch across a box edge.
- Mark a placed digit’s diagonal neighbours in your notes as soon as you place it.
- Hidden singles work the same way, with the diagonal neighbours added.
What changes from classic Sudoku
The extra rule is short but effective. Even a puzzle with few starting digits gets steady progress from the diagonal eliminations.