EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 82: 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 82 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 3 (expert and beyond), from the middle third of the book
Key technique
Forcing Chains
Hard steps
9 of 80 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), Advanced Innies (3+ sectors) (×2), Coloring/Multi-coloring, 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 6 · Multi-Sector Locking advanced
    Rules out 9 from R1C5, R2C5, R4C4, R4C6 and 2 more; 5 from R5C2, R6C2, R6C3.
  2. Step 9 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R6C6, R7C6; 2 from R6C6, R7C6; 5 from R7C5.
  3. Step 19 · Multi-Sector Locking advanced
    Rules out 5 from R1C7, R2C9, R3C7, R3C8 and 1 more; 2 from R6C4.
  4. Step 30 · Multi-Sector Locking advanced
    Rules out 4 from R8C6, R9C6.
  5. Step 32 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R3C5; 3 from R3C5; 2 from R3C6.
  6. Step 33 · Forcing Chains expert
    Rules out 4 from R6C6.
  7. Step 62 · Empty Rectangle advanced
    Rules out 6 from R2C1.
  8. Step 63 · Remote Pairs expert
    Rules out 2 from R4C3; 6 from R4C3.
  9. Step 65 · Coloring/Multi-coloring expert
    Rules out 6 from R7C1.

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.