EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 48: 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.

Puzzle
Killer sudoku, number 48 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 2 (expert and beyond), from the opening third of the book
Key technique
Forcing Chains
Hard steps
8 of 85 steps need an advanced or expert technique

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: Empty Rectangle (×3), Multi-Sector Locking (×2), Advanced Innies (3+ sectors), Coloring/Multi-coloring.

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 (8)
  1. Step 25 · Empty Rectangle advanced
    Rules out 7 from R4C7.
  2. Step 26 · Empty Rectangle advanced
    Rules out 9 from R4C7.
  3. Step 29 · Multi-Sector Locking advanced
    Rules out 1 from R1C8, R2C8, R3C8, R4C8 and 3 more; 9 from R4C9, R5C9, R7C8, R8C8 and 1 more.
  4. Step 32 · Advanced Innies (3+ sectors) advanced
    Places 4 in R4C1, 7 in R5C1 and rules out 4 from R1C1, R2C1, R4C2, R4C7 and 6 more; 7 from R2C1, R3C1, R5C2, R5C3 and 10 more; 8 from R5C6.
  5. Step 53 · Empty Rectangle advanced
    Rules out 5 from R9C1.
  6. Step 54 · Multi-Sector Locking advanced
    Rules out 3 from R2C9, R3C8, R3C9.
  7. Step 55 · Forcing Chains expert
    Rules out 9 from R1C6.
  8. Step 75 · Coloring/Multi-coloring expert
    Rules out 3 from R6C1, R8C2.

The book

Volume three: 150 new killers, none repeated from books 1 or 2. No starting digits, just cages and their totals, ramping from hard to brutal.

150 new 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.

On Amazon from 15 Dec About the book

Try a free sample puzzle (PDF) · prints on A4 or US Letter

More step-by-step solutions: Extreme Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3.