Hard Anti-Knight Sudoku

Cells a chess knight's move apart cannot share the same digit. A global constraint that shapes every row and column.

Easy Medium Hard Expert

Hard Anti-Knight Sudoku. Sparse givens and long cross-unit knight's chains make this a demanding solve — initialize all knight's eliminations before starting deductions.

5
3
9
1
8
7
8
1
7
4
3
5
9
4
7
2
1
4
8
3
7
5
8
4
9
9
6
Mistakes
0/3
Score
-
Time
00:00
Try Expert →
Progress0%
♞ Knight's move constraint active

What is Anti-Knight Sudoku?

Difficulty
★★★☆☆
3/5
Constraint Type
Anti-Constraints
Typical Givens
20–26
Avg. Solve (Hard)
24 min

Solving Techniques for Hard Level

Technique Description Level
Knight-Zone Mapping For each cell, mark all potential knight-move destinations (up to 8 cells). None may share the same digit as the source cell. Beginner
Corner and Edge Advantage Corner cells have only 2 knight-move neighbours; edge cells have at most 4. These restricted zones are easiest to resolve first. Beginner
Knight Chains Placing a digit can eliminate it from a chain of knight-move positions that span diagonally across the grid. Intermediate
Graph Coloring Model the knight-move network as a graph and two-color it to find cells that cannot share a digit. Advanced

Ready for the ultimate test? Try Expert Anti-Knight Sudoku — the hardest puzzles on Sudoku.by.

Average Solve Time by Difficulty

Easy
5 min
Medium
12 min
Hard
24 min
Expert
45 min
Want a full walkthrough of rules, strategies, and solving steps? How to Play Anti-Knight Sudoku →

Frequently Asked Questions — Hard Anti-Knight Sudoku

What makes hard Anti-Knight Sudoku difficult?
Hard Anti-Knight puzzles have sparse givens and require long knight's-move chains that span multiple units. You must simultaneously track row, column, box, and knight's-move constraints while maintaining a complete candidate grid — dropping any one of these often leads to a dead end.
How do I find a breakthrough in a hard Anti-Knight Sudoku?
Look for a digit that is restricted to only two cells across an entire row or column. Then check each candidate cell's knight's-move neighbors — if one of those neighbors already contains the digit, the candidate is eliminated, leaving only one option and breaking the puzzle open.
What is the knight's-move X-Wing pattern?
A knight's-move X-Wing occurs when a digit has exactly two candidate cells in each of two rows, and those cells are knight's-move distances apart in a symmetric pattern. This allows eliminations in multiple columns simultaneously, combining standard X-Wing logic with the knight's constraint.
How important is the full candidate initialization in hard Anti-Knight Sudoku?
Critical. Before any deductions, apply the knight's constraint from every given digit. Each given generates eliminations far beyond its own row, column, and box. Hard puzzles depend on these extended eliminations to be solvable, and missing them early will make the puzzle appear much harder than it is.
How long does a hard Anti-Knight Sudoku take to solve?
Expect 30–55 minutes for hard puzzles. Players who work through the full knight's-move initialization at the start can often shave 10–15 minutes off their solve time.

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