Techniques · killer sudoku

Forcing Chains

Try each candidate of one cell in turn. Every choice leads to the same result, so that result must be true.

In the walkthroughs, every Forcing Chains 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 Forcing Chains is used, those where it is the key technique first. Each link opens the full step-by-step solution.

Extreme Killer Sudoku 1 (146 of 150 puzzles)

• Puzzle 5 · Expert 3 · key technique
• Puzzle 13 · Expert 3 · key technique
• Puzzle 20 · Expert 2 · key technique
• Puzzle 21 · Expert 2 · key technique
• Puzzle 22 · Expert 2 · key technique
• Puzzle 25 · Expert 2 · key technique
• Puzzle 29 · Expert 2 · key technique
• Puzzle 31 · Expert 3 · key technique

Extreme Killer Sudoku 2 (147 of 150 puzzles)

• Puzzle 7 · Expert 3 · key technique
• Puzzle 10 · Expert 2 · key technique
• Puzzle 11 · Expert 2 · key technique
• Puzzle 15 · Expert 2 · key technique
• Puzzle 18 · Expert 2 · key technique
• Puzzle 19 · Expert 2 · key technique
• Puzzle 20 · Expert 2 · key technique
• Puzzle 25 · Expert 2 · key technique

Extreme Killer Sudoku 3 (143 of 150 puzzles)

• Puzzle 48 · Expert 2 · key technique
• Puzzle 49 · Expert 2 · key technique
• Puzzle 72 · Expert 2 · key technique
• Puzzle 78 · Expert 2 · key technique
• Puzzle 80 · Expert 2 · key technique
• Puzzle 83 · Expert 3 · key technique
• Puzzle 85 · Expert 2 · key technique
• Puzzle 87 · Expert 2 · key technique

Where it sits

See the whole ladder on hard killer sudoku techniques, or look a puzzle up by number under solutions.