a05506d2272aeb85788fe8c8093ef505
I wrote a program to brute-force them.
To finish the last one, I found it faster to use its transpose because of the way I ordered things.
I might try doing them by hand later (wink wink).
Touché.
Here is the hardest one I have generated. Harry can decide whether to let it post or to keep
it for the puzzle page. Two separate programs ranked it off the scale in difficulty. But it
can be brute-forced easily.
__6 7_8 __3
5__ 6__ ___
__3 ___ _67
__7 ___ __6
_1_ 45_ ___
___ __3 1__
___ _8_ __2
_3_ __2 4__
7_8 1__ ___