The unique solution has been verified with DLX.

- Code: Select all
`.------------------------------.------------------------------.------------------------------.`

| 1257 23479 12479 | 2468 1245679 14568 | 579 357 13458 |

| 135679 12456789 4567 | 35678 2356 256789 | 24569 234 35679 |

| 2348 1256 1235678 | 12478 345789 1479 | 45679 134 126789 |

:------------------------------+------------------------------+------------------------------:

| 12356789 45679 356 | 138 2456 123489 | 124567 138 12467 |

| 123468 134679 34679 | 2468 15678 12346789 | 12346789 78 123456 |

| 2578 1268 346789 | 5689 12345678 458 | 1234567 679 1245789 |

:------------------------------+------------------------------+------------------------------:

| 234567 24678 12458 | 19 13456789 1234689 | 2358 234589 12679 |

| 378 1689 145689 | 123456789 1234678 2578 | 126 12345689 3589 |

| 13568 13479 13489 | 13789 34568 35689 | 123478 67 235678 |

'------------------------------'------------------------------'------------------------------'

Solution in tiny text:

729461538614835927358297641965328714143679285287514369472153896896742153531986472

Can anyone find a logical path to this solution?

[edit]

- added box boundaries to grid.

A candidate grid without givens allows us to reduce the info to the absolute minimum, making it possible to generate harder Sudokus than with given numbers. A given number always eliminates 28 candidates simultaneously, but here each candidate can be eliminated individually. I have already found several puzzles that require brute force (guessing). Some of these have a SudoCue rating around 50000. The hardest Sudokus from ravel's list rate arount 25000.

SudoCue can solve it with the following techniques:

- 6x ALS-xz

- 3x Nishio

- 39 table contradictions

- 1 guess

Ruud