Anti-King Sudoku
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 a king's move?
A king's move covers all 8 adjacent cells: horizontally, vertically, and diagonally. No two king-move neighbours can contain the same digit.
How does Anti-King differ from Anti-Knight?
Anti-King forbids same digits within one step in any direction; Anti-Knight forbids same digits at L-shaped knight distances.