Expert Anti-King Sudoku

No two identical digits may touch diagonally (like a chess king's move). Every cell has up to 8 restricted neighbours.

Easy Medium Hard Expert

Expert Anti-King Sudoku. Every placement is forced by interleaved diagonal and standard logic. The hardest anti-king puzzles on the site — no guessing required.

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Mistakes
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Score
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Time
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Progress0%
♚ King's move constraint active

What is Anti-King Sudoku?

Difficulty
★★★☆☆
3/5
Constraint Type
Anti-Constraints
Typical Givens
22–28
Avg. Solve (Expert)
48 min

Solving Techniques for Expert Level

Technique Description 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 Time by Difficulty

Easy
5 min
Medium
13 min
Hard
26 min
Expert
48 min
Want a full walkthrough of rules, strategies, and solving steps? How to Play Anti-King Sudoku →

Frequently Asked Questions — Expert Anti-King Sudoku

Is expert Anti-King Sudoku solvable without guessing?
Yes. Every expert Anti-King Sudoku on Sudoku.by has a unique solution reachable through pure logic. The king's constraint at expert level creates enough structure to resolve even the most difficult positions without bifurcation.
What advanced techniques are needed for expert Anti-King Sudoku?
Expert puzzles require king's-move forcing chains: sequences where assuming digit X in cell A leads to forced placements that eventually contradict another cell, proving that X cannot go in A. You may also need anti-king-aware X-Wings, where the king's constraint determines which rows or columns the pattern spans.
How does parity interact with the king's-move rule at expert level?
The king's constraint creates parity effects on diagonal lines: if a digit occupies a cell, it cannot appear in either adjacent diagonal direction. In dense king's-constraint grids, this means some digits are forced into specific diagonal patterns. Exploiting these patterns is key to expert-level breakthroughs.
How many given digits does an expert Anti-King Sudoku have?
Expert puzzles typically provide fewer than 25 given digits. The combination of sparse givens and the king's constraint means the board looks open, but every placement is tightly constrained from multiple directions.
How long does an expert Anti-King Sudoku take to solve?
Expert puzzles take most players 60–90 minutes. If you're stuck, verify that you have applied the king's-move eliminations exhaustively from every given digit and every digit placed so far — a missed diagonal elimination is the most common source of errors at this level.

More questions? See the full Anti-King Sudoku guide.