EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 97: 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 97 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 2 (expert and beyond), from the middle third of the book
Key technique
Remote Pairs
Hard steps
10 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: Remote Pairs

A chain of cells that all hold the same pair alternates between the two digits. Cells that see both ends of an odd-length link cannot hold either digit.

Other advanced and expert techniques in this solve: Multi-Sector Locking (×2), X-Wing/Swordfish (×2), 2-String Kite, Advanced Innies (3+ sectors), Empty Rectangle, Forcing Chains, XY-Wing.

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 (10)
  1. Step 32 · 2-String Kite advanced
    Rules out 7 from R3C7.
  2. Step 33 · Multi-Sector Locking advanced
    Rules out 4 from R1C7, R2C7.
  3. Step 34 · Advanced Innies (3+ sectors) advanced
    Rules out 8 from R5C5; 9 from R5C5.
  4. Step 36 · Multi-Sector Locking advanced
    Rules out 8 from R7C4, R8C4.
  5. Step 37 · Remote Pairs expert
    Rules out 6 from R5C5.
  6. Step 75 · X-Wing/Swordfish advanced
    Rules out 3 from R9C4, R9C9.
  7. Step 76 · Empty Rectangle advanced
    Rules out 8 from R2C7.
  8. Step 80 · X-Wing/Swordfish advanced
    Rules out 8 from R4C2, R4C4, R4C6.
  9. Step 81 · XY-Wing advanced
    Rules out 6 from R6C6.
  10. Step 87 · Forcing Chains expert
    Rules out 2 from R1C1.

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.