The New Sudoku Players' Forum

[zennehoy]

Usually when I tell my cellphone to generate a hard Sudoku, it takes me exactly one subway trip home to solve, with the most difficult solving strategy being on the order of a Y-Wing. Well, this time was different:

Code: Select all

4..|...|51.
.6.|4..|8..
...|...|.93
---+---+---
.2.|3..|...
...|..8|32.
...|.6.|..8
---+---+---
53.|.9.|1..
1.2|.3.|..9
..8|..7|.35


with this being as far as I got (after ALSs and 2 AICs):

Code: Select all

4   8    379 |79   2    39   |5   1   6
39  6    1359|4    15   1359 |8   7   2
2   157  157 |1567 8    156  |4   9   3
-------------+---------------+-----------
8   2    1459|3    1457 1459 |679 456 147
679 1459 1456|159  1457 8    |3   2   147
379 145  1349|1259 6    12459|79  45  8
-------------+---------------+-----------
5   3    467 |268  9    246  |1   468 47
1   47   2   |568  3    456  |67  468 9
69  49   8   |16   14   7    |2   3   5

48..2.516.6.4..8722...8.49382.3..........832.....6...853..9.1..1.2.3...9..8..7235

After staring at the board for 3 trips now with no progress I'm truely and royally stumped. Any ideas on how to keep going?
Thanks in advance!
Zen

[RW]

Hi zennehoy

Code: Select all

4   8    379 |79   2    39   |5   1   6
39  6    1359|4    15   1359 |8   7   2
2   157  157 |1567 8    156  |4   9   3
-------------+---------------+-----------
8   2    1459|3    1457 1459 |679 456 147
679 1459 1456|159  1457 8    |3   2   147
379 145  1349|1259 6    12459|79  45  8
-------------+---------------+-----------
5   3    467 |268  9    246  |1   468 47
1   47   2   |568  3    456  |67  468 9
69  49   8   |16   14   7    |2   3   5

First, there is a BUG-lite pattern in r1c36,r2c136,r6c13. The fastest way to spot it is as a layered BUG-lite. Candidate 3 already only appears in these cells, then if r6c13=9 => r5c4=9 => r12c6=9 which completes the layered BUG-lite => r6c13<>9.

Next, there's a short forcing chain:

[r12c3]=9=[r2c1]=3=[r6c1]=7=[r6c7]=9=[r4c7]

which implies that if r12c3<>9 then r4c7=9, any way r4c3<>9. You should be able to finish from here.

RW