Anti-King Sudoku
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How to play Anti-King Sudoku
Standard Sudoku rules apply. Additional rule: no two diagonally adjacent cells (or orthogonally adjacent) may share the same digit. A king on a chess board can reach all 8 surrounding cells — none of those cells can share a digit.
Full guide →
No two cells a king's move apart may contain the same digit
Easy
Anti-King Sudoku Easy
Medium
Anti-King Sudoku Medium
Hard
Anti-King Sudoku Hard
Expert
Anti-King Sudoku Expert
What is Anti-King Sudoku?
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
| Constraint type | Anti-Constraints |
| Typical givens | 22–28 |
| Difficulty rating | ★★★☆☆ 3/5 |
| Avg. solve time — Easy | 5 min |
| Avg. solve time — Medium | 13 min |
| Avg. solve time — Hard | 26 min |
| Avg. solve time — Expert | 48 min |
How to Solve Anti-King Sudoku
| Technique | What it does | Level |
|---|---|---|
| Diagonal Exclusion | The king constraint extends the exclusion zone to all 8 neighbours including diagonals. Apply diagonal exclusions before standard row/col/box logic. | Beginner |
| Corner Restriction | Corner cells (e.g., r1c1) only have 3 king-move neighbours. Start with corners and edges to build initial placements. | Intermediate |
| King-Chain Elimination | When a digit is placed, eliminate it simultaneously from all 8 surrounding cells. | Intermediate |
| Parity via King's Move | In Anti-King, consecutive digits often become mutually king-move incompatible — trace valid placement paths using this property. | Advanced |
Average Solve Times
Easy
5 min
Medium
13 min
Hard
26 min
Expert
48 min
Frequently Asked 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.