Techniques · sudoku
ALS-XZ
Two almost-locked sets (n cells with n+1 candidates) share a restricted digit X. Then a digit Z common to both must be in one of them, so cells seeing all of its copies cannot be Z.
In the walkthroughs, every ALS-XZ step shades the cells of the pattern and names the cell and digit it proves, so you can see the move on the grid rather than read about it. Press “Skip to next hard step” to jump straight to it.
Worked examples
Puzzles from the books where ALS-XZ is used, those where it is the key technique first. Each link opens the full step-by-step solution.
Extreme Sudoku 1 (150 of 150 puzzles)
- Puzzle 5 · Expert 5 · key technique
- Puzzle 6 · Expert 5 · key technique
- Puzzle 9 · Expert 5 · key technique
- Puzzle 10 · Expert 5 · key technique
- Puzzle 11 · Expert 5 · key technique
- Puzzle 12 · Expert 5 · key technique
- Puzzle 13 · Expert 5 · key technique
- Puzzle 14 · Expert 6 · key technique
Extreme Sudoku 2 (150 of 150 puzzles)
- Puzzle 2 · Expert 5 · key technique
- Puzzle 5 · Expert 5 · key technique
- Puzzle 8 · Expert 5 · key technique
- Puzzle 9 · Expert 6 · key technique
- Puzzle 10 · Expert 6 · key technique
- Puzzle 11 · Expert 6 · key technique
- Puzzle 13 · Expert 7 · key technique
- Puzzle 14 · Expert 5 · key technique
Extreme Sudoku 3 (150 of 150 puzzles)
- Puzzle 2 · Expert 5 · key technique
- Puzzle 3 · Expert 5 · key technique
- Puzzle 4 · Expert 5 · key technique
- Puzzle 5 · Expert 5 · key technique
- Puzzle 9 · Expert 5 · key technique
- Puzzle 10 · Expert 5 · key technique
- Puzzle 11 · Expert 5 · key technique
- Puzzle 15 · Expert 5 · key technique
Where it sits
See the whole ladder on hard sudoku techniques, or look a puzzle up by number under solutions.
