Extreme Killer Sudoku 1, puzzle 24: step-by-step solution
Step through the whole solution, or skip to the hard parts. Blue digits are placed by the walkthrough; red strike-through marks a candidate being ruled out.
Blue digits are placed by the walkthrough. Red strike-through marks a candidate being ruled out. Cells are named by row and column: R3C5 is row 3, column 5. Arrow keys step too.
The key technique: Coloring/Multi-coloring
Following one digit’s strong links, cells get two colours: one colour is true and the other is false. A cell that sees both colours cannot hold the digit.
Other advanced and expert techniques in this solve: Multi-Sector Locking (×2), Forcing Chains.
Every move above the basics is listed on the killer sudoku techniques page, each with a one-sentence explanation and worked examples from the books.
The hard steps, in text (5)
- Step 23 · Multi-Sector Locking advanced
Rules out 9 from R1C2. - Step 26 · Coloring/Multi-coloring expert
Rules out 1 from R7C8. - Step 27 · Forcing Chains expert
Rules out 7 from R2C1, R2C3, R6C2, R7C2 and 1 more; 6 from R7C2, R8C2. - Step 56 · Multi-Sector Locking advanced
Rules out 1 from R7C6, R8C6. - Step 57 · Coloring/Multi-coloring expert
Rules out 8 from R5C6, R7C5.
The book
No starting digits at all: just cages and their totals. Sudoku rules, plus arithmetic, plus a lot of nerve.
150 puzzles. Expert and beyond. Puzzles by M. J. Bailey. Paperback, 5 × 8 in, 196 pages, £9.99 / $11.99. Every solution in the book carries a QR code to its own walkthrough, so you can check one step without seeing the whole answer.
Try a free sample puzzle (PDF) · prints on A4 or US Letter
More step-by-step solutions: Extreme Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.