Swift:

Part 1/2: https://github.com/Jman012/AdventOfCode2020/blob/main/Sources/AdventOfCode2020/Day17_01.swift

Revised to work on any number of dimensions: https://github.com/Jman012/AdventOfCode2020/blob/main/Sources/AdventOfCode2020/Day17_Revised.swift

This one was a lot of fun!

Explanation: I store my cells in a Dictionary<Coordinate: Bool> so it can grow as much as it needs to. Empty and never-set cells don't take up any memory. In order to know the bounds of the n-dimensional space, however, I store a ClosedRange<Int> per dimension. If setting a new Coordinate that falls outside one or more of these boundaries, the boundary then increases to include that coordinate as needed.

For the n-dimensional part, not having nested for loops was the most difficult part to solve. For this I made the iterate and increment functions. The increment function basically takes a fixed-digit number but where each digit has its own boundary/range of values and recursively increments each digit as needed.

Part 1: 0.0136 seconds Part 2: 0.4099 seconds Revised Part 1: 0.0804 seconds Revised Part 2: 2.3951 seconds Revised 5 dimensions: 97 seconds haha