How to Play Anti-King Sudoku
No two cells a king's move apart may contain the same digit
The Rules
Standard Sudoku rules apply: fill every row, column, and 3×3 box with the digits 1–9, each appearing exactly once.
Anti-King Sudoku adds a chess-inspired constraint: cells that would be reachable in a single king move (orthogonally or diagonally adjacent) cannot share the same digit. This extends the non-repeat rule beyond rows, columns, and boxes to include diagonal neighbours, significantly tightening the constraint space throughout the grid.
At a Glance
How to Solve Anti-King Sudoku
Common Questions
What is Anti-King Sudoku? ▾
Anti-King Sudoku is a variant where no two diagonally adjacent cells may contain the same digit. Combined with standard Sudoku rules (which already forbid matching digits in the same row, column, and box), this means a digit cannot appear in any of the eight cells surrounding a given cell.
Why is it called Anti-King? ▾
The name comes from chess: a king can move to any of the eight adjacent squares (horizontally, vertically, or diagonally). The Anti-King constraint says no digit may be repeated within a king's move of any placed digit — it's the opposite of the king's reach being unrestricted.
How many cells does the anti-king constraint affect? ▾
Each interior cell has eight neighbours (up to eight for corner and edge cells). All eight must hold different digits from the placed cell, on top of the standard uniqueness rules. Cells in the top-left to bottom-right diagonal neighbourhood are constrained in ways that standard Sudoku doesn't cover.
Is Anti-King Sudoku harder than regular Sudoku? ▾
Easy Anti-King puzzles resolve faster than classic Sudoku because the extra diagonal constraint eliminates more candidates. Hard and expert puzzles compensate with fewer givens, and the diagonal interactions create subtle deduction chains that can be difficult to spot.
What is the best first move in Anti-King Sudoku? ▾
Focus on corner cells first — they have the fewest anti-king neighbours (only 3 for a true corner). Then look at cells near already-placed digits and check how many of the eight neighbours already have that digit. Dense clustering of given digits often creates immediate anti-king placements.
How long does Anti-King Sudoku take to solve? ▾
Easy puzzles take 6–15 minutes. Medium puzzles run 15–30 minutes. Hard puzzles average 30–60 minutes and expert puzzles can take 60–90 minutes. The diagonal constraint makes early progress fast but creates subtle interactions in the middle and end game.