Extreme Killer Sudoku 1, puzzle 70: 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: Forcing Chains
Try each candidate of one cell in turn. Every choice leads to the same result, so that result must be true.
Other advanced and expert techniques in this solve: 2-String Kite, Advanced Innies (3+ sectors), Finned Fish, Multi-Sector Locking.
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 15 · Advanced Innies (3+ sectors) advanced
Places 5 in R1C5, 7 in R1C6 and rules out 5 from R1C1, R1C3, R1C4, R1C7 and 12 more; 7 from R1C1, R1C2, R1C3, R1C4 and 13 more; 1 from R4C4. - Step 46 · Multi-Sector Locking advanced
Rules out 8 from R4C7, R8C7, R9C7; 9 from R7C7. - Step 51 · Forcing Chains expert
Rules out 6 from R1C7. - Step 63 · 2-String Kite advanced
Rules out 8 from R9C5. - Step 64 · Finned Fish expert
Rules out 2 from R7C5, R8C5.
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.