EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 143: 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
Sudoku, number 143 of 150 in Extreme Sudoku 3
Difficulty
Expert 6 (expert and beyond), from the final, hardest third of the book
Key technique
XY-Chain
Hard steps
18 of 40 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: XY-Chain

A chain of two-candidate cells, each linked to the next. Whichever way the start cell goes, one end of the chain holds the digit, so cells seeing both ends cannot.

Other advanced and expert techniques in this solve: Nice Loops/AICs (×2), 2-String Kite, ALS-XZ, Cell Forcing Chains, Finned Fish, W-Wing, WXYZ-Wing.

Every move above the basics is listed on the sudoku techniques page, each with a one-sentence explanation and worked examples from the books.

The hard steps, in text (18)
  1. Step 7 · Cell Forcing Chains expert
    Rules out 1 from R1C3.
  2. Step 9 · Finned Fish expert
    Rules out 1 from R8C1.
  3. Step 10 · ALS-XZ expert
    Rules out 2 from R4C1, R6C1.
  4. Step 12 · Nice Loops/AICs expert
    Rules out 4 from R8C4.
  5. Step 13 · Nice Loops/AICs expert
    Rules out 1 from R7C7.
  6. Step 15 · XY-Chain expert
    Rules out 7 from R6C7, R9C9.
  7. Step 19 · 2-String Kite advanced
    Rules out 3 from R9C2.
  8. Step 20 · XY-Chain expert
    Rules out 2 from R4C9, R6C4, R6C5.
  9. Step 22 · W-Wing advanced
    Rules out 9 from R6C1.
  10. Step 23 · XY-Chain expert
    Rules out 6 from R8C4.
  11. Step 24 · XY-Chain expert
    Rules out 6 from R6C4.
  12. Step 25 · XY-Chain expert
    Rules out 1 from R7C5.
  13. Step 26 · XY-Chain expert
    Rules out 3 from R5C3.
  14. Step 28 · XY-Chain expert
    Rules out 3 from R8C4, R9C3.
  15. Step 29 · XY-Chain expert
    Rules out 3 from R9C4.
  16. Step 30 · WXYZ-Wing expert
    Rules out 2 from R3C3, R5C1.
  17. Step 35 · XY-Chain expert
    Rules out 1 from R7C2.
  18. Step 36 · XY-Chain expert
    Rules out 3 from R7C4.

The book

Volume three: 150 new classic 9×9 grids, none repeated from books 1 or 2, 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.

On Amazon from 8 Dec About the book

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More step-by-step solutions: Extreme Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Killer Sudoku 3.