EXTREMEPUZZLE BOOKS

Extreme 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
Sudoku, number 148 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the final, hardest third of the book
Key technique
XY-Chain
Hard steps
14 of 38 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: ALS-XZ (×3), 2-String Kite, Cell Forcing Chains, Finned Fish, Nice Loops/AICs, WXYZ-Wing, XY-Wing, XYZ-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 (14)
  1. Step 4 · 2-String Kite advanced
    Rules out 3 from R3C5.
  2. Step 5 · XY-Chain expert
    Rules out 4 from R3C8.
  3. Step 6 · WXYZ-Wing expert
    Rules out 1 from R7C2, R8C2.
  4. Step 7 · ALS-XZ expert
    Rules out 9 from R2C2, R3C2.
  5. Step 10 · XY-Chain expert
    Rules out 9 from R7C1.
  6. Step 15 · XY-Chain expert
    Rules out 4 from R1C8, R2C8.
  7. Step 16 · Cell Forcing Chains expert
    Rules out 3 from R2C1.
  8. Step 20 · XYZ-Wing advanced
    Rules out 9 from R4C7.
  9. Step 21 · Finned Fish expert
    Rules out 9 from R5C5.
  10. Step 23 · XY-Chain expert
    Rules out 2 from R1C5, R3C5.
  11. Step 24 · ALS-XZ expert
    Rules out 4 from R1C7.
  12. Step 27 · Nice Loops/AICs expert
    Rules out 2 from R1C4.
  13. Step 28 · ALS-XZ expert
    Rules out 4 from R2C6.
  14. Step 33 · XY-Wing advanced
    Rules out 6 from R5C4, R5C5.

The book

Volume two: 150 new classic 9×9 grids, none repeated from book 1, 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 Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.