7
$\begingroup$
 8  .  . | .  .  . | .  .  6 
 .  .  4 | .  .  . | .  .  . 
 .  .  . | .  .  . | 9  1  . 
---------+---------+--------
 .  .  . | .  2  . | .  .  . 
 .  .  9 | 3  .  . | .  .  . 
 .  .  . | .  .  . | .  .  . 
---------+---------+--------
 .  .  . | 9  .  7 | .  .  . 
 9  .  . | 6  3  . | 4  .  . 
 .  .  . | .  .  . | 1  .  . 
  • Normal sudoku rules apply.
  • Long diagonals contain only unique values.
  • If A is a box-center, and A and B are a knight's move apart, then A and B ought to be different.

A knight's move constitutes going up/down by two followed by going left/right by one, or going up/down by one followed by going left/right by two:

. . B . B . .
. B . . . B .
. . . A . . .
. B . . . B .
. . B . B . .
$\endgroup$
  • 1
    $\begingroup$ Does "diagonals" mean just the two long diagonals, or every line at 45 degrees? [EDITED to add:] Duh, must be the former since there are two diagonally-adjacent 1s in the grid already. $\endgroup$ – Gareth McCaughan Dec 10 '19 at 22:35
  • 14
    $\begingroup$ It looks like the 9s in R2C4 and R4C5 contradict the pseudo-knight move restriction. Is that intended? $\endgroup$ – HTM Dec 10 '19 at 22:38
  • 2
    $\begingroup$ The same with 5 at the top right. $\endgroup$ – Moti Dec 11 '19 at 1:25
  • 2
    $\begingroup$ I believe this is unsolvable. I've tried twice to solve it deterministically, both times resulting in contradictions. Are you able to check that a solution exists satisfying the conditions? $\endgroup$ – Matthew Jensen Dec 11 '19 at 4:01
  • 1
    $\begingroup$ The puzzle should be solvable now. I updated the puzzle itself and the instructions. Thanks for your feedback. $\endgroup$ – Joris Schellekens Dec 11 '19 at 10:01
3
$\begingroup$

A very tough Sudoku, but I think I got it:

enter image description here

| improve this answer | |
$\endgroup$
  • $\begingroup$ Congratulations! $\endgroup$ – Joris Schellekens Dec 14 '19 at 21:06

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