EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 148: 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 148 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 2 (expert and beyond), from the final, hardest third of the book
Key technique
Coloring/Multi-coloring
Hard steps
12 of 86 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: Coloring/Multi-coloring

Following one digit’s strong links, cells get two colours: one colour is true and the other is false. A cell that sees both colours cannot hold the digit.

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

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 22 · Multi-Sector Locking advanced
    Rules out 5 from R7C6, R7C7, R8C7, R8C8 and 1 more.
  2. Step 50 · Multi-Sector Locking advanced
    Rules out 6 from R3C8.
  3. Step 51 · Forcing Chains expert
    Rules out 5 from R1C4, R1C5, R1C8, R2C8; 7 from R1C4, R1C5, R1C6, R1C7 and 8 more; 4 from R1C8, R2C8, R6C7.
  4. Step 54 · Skyscraper advanced
    Rules out 7 from R4C4.
  5. Step 62 · Advanced Innies (3+ sectors) advanced
    Rules out 8 from R4C8.
  6. Step 63 · Coloring/Multi-coloring expert
    Rules out 7 from R4C5.
  7. Step 64 · Skyscraper advanced
    Rules out 7 from R3C6.
  8. Step 66 · Coloring/Multi-coloring expert
    Rules out 9 from R1C7.
  9. Step 67 · 2-String Kite advanced
    Rules out 9 from R4C2.
  10. Step 68 · Empty Rectangle advanced
    Rules out 9 from R4C4.
  11. Step 69 · Empty Rectangle advanced
    Rules out 9 from R1C1.
  12. Step 72 · Advanced Innies (3+ sectors) advanced
    Rules out 2 from R3C7; 3 from R3C8, R4C8.

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.