EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 150: 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 150 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 2 (expert and beyond), from the final, hardest third of the book
Key technique
Forcing Chains
Hard steps
12 of 118 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 (×5), Advanced Innies (3+ sectors) (×2), 2-String Kite, Empty Rectangle, Remote Pairs, XYZ-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 (12)
  1. Step 11 · Multi-Sector Locking advanced
    Rules out 9 from R1C3, R1C4, R1C5.
  2. Step 33 · Multi-Sector Locking advanced
    Rules out 4 from R4C1, R4C2, R4C3, R4C4 and 1 more; 1 from R4C6, R4C7.
  3. Step 35 · Advanced Innies (3+ sectors) advanced
    Rules out 7 from R2C5; 8 from R2C5; 4 from R2C6.
  4. Step 36 · Multi-Sector Locking advanced
    Rules out 3 from R5C6, R6C6, R7C6, R8C6 and 1 more.
  5. Step 37 · Empty Rectangle advanced
    Rules out 3 from R4C3.
  6. Step 39 · Forcing Chains expert
    Rules out 2 from R1C1, R1C3, R1C4, R1C5; 7 from R2C1; 5 from R2C3, R2C4.
  7. Step 56 · 2-String Kite advanced
    Rules out 2 from R9C2.
  8. Step 57 · Multi-Sector Locking advanced
    Rules out 3 from R8C1; 8 from R8C1.
  9. Step 58 · Advanced Innies (3+ sectors) advanced
    Rules out 3 from R1C5; 8 from R1C5; 7 from R8C5, R9C5.
  10. Step 70 · XYZ-Wing advanced
    Rules out 7 from R2C3.
  11. Step 87 · Multi-Sector Locking advanced
    Rules out 1 from R4C2, R8C3, R9C2, R9C3.
  12. Step 104 · Remote Pairs expert
    Rules out 3 from R7C2, R8C2; 5 from R7C2, R8C2.

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.