EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 75: 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 75 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 2 (expert and beyond), from the middle third of the book
Key technique
Forcing Chains
Hard steps
9 of 91 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: Multi-Sector Locking (×3), 2-String Kite (×2), Advanced Innies (3+ sectors), Empty Rectangle, Remote Pairs.

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 18 · Multi-Sector Locking advanced
    Rules out 8 from R7C1, R7C2, R8C1, R8C2 and 1 more; 9 from R9C1.
  2. Step 19 · Advanced Innies (3+ sectors) advanced
    Rules out 2 from R3C4; 5 from R9C4.
  3. Step 31 · 2-String Kite advanced
    Rules out 1 from R6C6.
  4. Step 33 · Empty Rectangle advanced
    Rules out 1 from R6C3.
  5. Step 34 · Multi-Sector Locking advanced
    Rules out 7 from R1C1, R1C2, R1C3, R2C1 and 6 more.
  6. Step 37 · Multi-Sector Locking advanced
    Rules out 4 from R4C9.
  7. Step 38 · Forcing Chains expert
    Rules out 8 from R1C4.
  8. Step 76 · 2-String Kite advanced
    Rules out 6 from R8C2.
  9. Step 78 · Remote Pairs expert
    Rules out 6 from R2C7, R3C7, R7C9, R8C9; 2 from R7C9, R8C9, R9C9.

The book

Volume two: 150 new killers, none repeated from book 1. 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.

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