| 5 | 2 | 7 | ||||||
| 6 | 8 | 1 | ||||||
| 4 | 2 | 3 | ||||||
| 9 | 1 | 7 | 8 | |||||
| 5 | 1 | 9 | 6 | |||||
| 7 | 9 | |||||||
| 8 | 3 | |||||||
| 5 | 8 | |||||||
| 1 | 4 |
Master Sudoku
Fill the grid so every row, every column and every three-by-three box contains each digit from 1 to 9 exactly once. At least one step needs an XY-chain: a run of two-candidate cells that loops back to the same digit at both ends. Nothing here needs guessing.
What makes this puzzle Master?
This grid has 25 clues. Solving it without guessing requires at most a XY-Chain. We rate difficulty by the hardest logical technique a puzzle actually needs — not by how many digits we removed. Two puzzles with the same number of clues can be worlds apart, which is why clue count alone makes such a poor difficulty label.
Every technique this engine uses is documented, each with a worked example from a real puzzle: see solving techniques. Prefer paper? Printable Master sudoku as a free PDF.
Other difficulties
- Very Easy sudoku — pure scanning, nothing but singles
- Easy sudoku — adds locked candidates and pairs
- Medium sudoku — adds triples and quads, and fewer clues
- Hard sudoku — needs an X-Wing or an XY-Wing
- Expert sudoku — needs colouring, a Swordfish or an XYZ-Wing
- Master sudoku — needs an XY-chain