Extreme Killer Sudoku 1, puzzle 104: 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), Advanced Innies (3+ sectors), 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 (6)
- Step 13 · Multi-Sector Locking advanced
Rules out 9 from R5C6, R6C6. - Step 14 · Advanced Innies (3+ sectors) advanced
Places 1 in R6C5 and rules out 4 from R1C4, R4C4, R5C4, R6C4; 1 from R1C5, R4C4, R5C4, R5C6 and 6 more; 8 from R4C4, R5C4. - Step 21 · Multi-Sector Locking advanced
Rules out 7 from R1C5, R1C6, R3C6. - Step 56 · Coloring/Multi-coloring expert
Rules out 8 from R3C2. - Step 57 · Forcing Chains expert
Rules out 4 from R1C5. - Step 77 · Coloring/Multi-coloring expert
Rules out 7 from R5C1.
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.