EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 1, puzzle 144: 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 144 of 150 in Extreme Killer Sudoku 1
Difficulty
Expert 2 (expert and beyond), from the final, hardest third of the book
Key technique
Forcing Chains
Hard steps
10 of 90 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: Advanced Innies (3+ sectors) (×4), Multi-Sector Locking (×4), Coloring/Multi-coloring.

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 23 · Multi-Sector Locking advanced
    Rules out 1 from R1C5, R1C6; 4 from R4C1, R4C2, R5C5, R5C6; 9 from R5C3, R6C3, R7C3, R8C3 and 1 more.
  2. Step 28 · Multi-Sector Locking advanced
    Rules out 6 from R6C1.
  3. Step 29 · Advanced Innies (3+ sectors) advanced
    Rules out 3 from R5C5, R5C6; 5 from R5C8, R6C1; 7 from R6C1.
  4. Step 32 · Forcing Chains expert
    Rules out 8 from R1C7.
  5. Step 46 · Multi-Sector Locking advanced
    Rules out 9 from R7C4, R7C5, R8C2.
  6. Step 49 · Advanced Innies (3+ sectors) advanced
    Rules out 7 from R4C4, R4C5, R4C6.
  7. Step 52 · Advanced Innies (3+ sectors) advanced
    Rules out 8 from R6C1; 1 from R6C8.
  8. Step 72 · Multi-Sector Locking advanced
    Rules out 1 from R7C5.
  9. Step 74 · Advanced Innies (3+ sectors) advanced
    Rules out 8 from R3C5.
  10. Step 75 · Coloring/Multi-coloring expert
    Rules out 2 from R8C4.

The book

No starting digits at all: just cages and their totals. Sudoku rules, plus arithmetic, plus a lot of nerve.

150 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 Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.