4
1
2
3
5
8
9
7
6
3
7
9
4
2
6
5
8
1
6
5
8
9
1
7
3
4
2
2
8
3
6
4
5
7
9
1
9
1
4
7
3
2
6
5
8
5
7
6
8
9
1
2
3
4
8
3
9
5
6
7
1
2
4
1
6
7
2
4
3
8
9
5
4
2
5
1
8
9
7
6
3

This Sudoku Puzzle has 20 steps and it is solved using undefined, Hidden Single, Bivalue Universal Grave + 1, Naked Single, Full House techniques.

Naked Single Explanation
Hidden Single Explanation
Full House Explanation
Try To Solve This Puzzle

Solution Steps:

  1. W-Wing: 9/1 in r2c7,r8c9 connected by 1 in r5c79 => r2c9,r8c7<>9
  2. Row 2 / Column 7 → 9 (Hidden Single)
  3. Row 8 / Column 9 → 9 (Hidden Single)
  4. Bivalue Universal Grave + 1 => r2c8<>4, r2c8<>7
  5. Row 2 / Column 8 → 1 (Naked Single)
  6. Row 2 / Column 4 → 4 (Naked Single)
  7. Row 2 / Column 9 → 7 (Full House)
  8. Row 3 / Column 8 → 4 (Full House)
  9. Row 3 / Column 6 → 1 (Full House)
  10. Row 5 / Column 9 → 1 (Full House)
  11. Row 8 / Column 8 → 8 (Naked Single)
  12. Row 4 / Column 8 → 7 (Full House)
  13. Row 5 / Column 7 → 8 (Full House)
  14. Row 8 / Column 7 → 1 (Full House)
  15. Row 5 / Column 4 → 7 (Naked Single)
  16. Row 4 / Column 6 → 4 (Full House)
  17. Row 7 / Column 6 → 7 (Full House)
  18. Row 5 / Column 2 → 4 (Full House)
  19. Row 7 / Column 4 → 1 (Full House)
  20. Row 4 / Column 2 → 8 (Full House)
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