Started 4 days late so coming up from behind. Day 5 was the first solution I am somewhat proud of. I used interval arithmetics. I had to somewhat extend a class interval from pyinterval into something I called PointedInterval. In the end part 2 was completed in 0.32 seconds. It does not reverse engineer the solution starting from 0 location and inverse mapping until you find a seed (that was how I was initially planning to do it). It maps forward everything as intervals. There is a bit of a boiler plate which is in the utils file.