They updated the text slightly after a while since a lot of people got confused by the example (me included). In short, the top left coordinate in the z0 layer is not the same in each iteration and moves around depending on where there are active satellites.

Struggled for about an hour trying to make sense of the examples (and thought they meant the space wrapped around which created a real headache with a growing universe ).

I settled for storing the active satellites in a map, keyed on coordinates. Then I ran each iteration and checked all positions within my active state plus one in each direction.

Here is my solution.

Part 2 was simply extending part 1 with an extra dimension so only posted that.

@bjorng nice to use Stream.iterate() |> Enum.drop(6), also realised reading your code that I was a bit silly to filter my Map and use Enum.count since I also only store the active satellites in my map.

Oh boy, I get it now! I was looking for something in the instructions, but it’s how the examples are displayed. The frame of view is moving!
I could have ignored the examples but it bothered me that my understanding after which I write the algorithm wouldn’t even comply with the example. Alright… let’s see where to find the motivation to solve this now…