EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 1, puzzle 36: 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 36 of 150 in Extreme Killer Sudoku 1
Difficulty
Expert 2 (expert and beyond), from the opening third of the book
Key technique
Forcing Chains
Hard steps
9 of 97 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: Advanced Innies (3+ sectors) (×4), Multi-Sector Locking (×2), 2-String Kite, 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 (9)
  1. Step 13 · Multi-Sector Locking advanced
    Rules out 8 from R5C4.
  2. Step 14 · Advanced Innies (3+ sectors) advanced
    Rules out 3 from R4C7, R5C4; 8 from R4C7, R5C3, R5C6; 9 from R5C3, R5C4, R5C6.
  3. Step 16 · Advanced Innies (3+ sectors) advanced
    Rules out 7 from R5C6.
  4. Step 17 · Forcing Chains expert
    Rules out 6 from R5C4.
  5. Step 21 · Advanced Innies (3+ sectors) advanced
    Places 9 in R4C4 and rules out 9 from R1C4, R2C4, R3C4, R4C3 and 1 more.
  6. Step 67 · Multi-Sector Locking advanced
    Rules out 3 from R4C8.
  7. Step 71 · 2-String Kite advanced
    Rules out 3 from R1C9.
  8. Step 73 · Advanced Innies (3+ sectors) advanced
    Rules out 4 from R2C7.
  9. Step 74 · Coloring/Multi-coloring expert
    Rules out 8 from R4C8.

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.

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