My brute force approach worked until arround level 120, then I applied some preprocessng to the board, which improved the performance by about 20% for most boards. But over 60 minutes solving time was far to much, so I sat down with pencil and paper and worked out a solution. From then on the worst solving time was about 0.2 seconds, level 513 took 0.0045599937439 seconds. Why are there no bigger levels?
Finally finished this after dropping it a few years ago. Cheap ass Python implementation with just one optimization and just brute-forcing my way through, takes 2-3 minutes per level on the last ~15 levels. I know I should've probably looked for another optimization…
