All the daily levels are built by hand. I struggled to come up with a good random level generator. You can see my feeble attempts in the Edit page (via the hamburger menu) by giving the dice button a few sad clicks.
I did originally try to measure the difficulty computationally by running the solver and timing it, but it didn't really line up with what humans would find difficult. Now I'm just eyeballing it.
I did originally try to measure the difficulty computationally by running the solver and timing it, but it didn't really line up with what humans would find difficult. Now I'm just eyeballing it.