Day 24 Notes
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| Part 1 |
+--------+
$ elixir day24part1.exs
326
Thoughts:
Interesting. Need to work out how to implement a hexagonal grid.
Use Enum.chunk_while to parse the variable-length `e`, `ne`, `s', `sw` etc. input tokens.
I decided to do it like this: Use x, y coordinates, but horizontally adjacent cells are 2 x units
apart. Diagonally adjacent cells are 1 x unit and 1 y unit apart.
/ \ (0,0)
| |
/ \ / \ (1, -1)
| | |
\ / \ /
↑
(-1, -1)
Define a tranlation vector for each direction, then we can walk the directions, and take the sum
of all the translations.
Store the black cells in a MapSet, and count them once we're done.
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| Part 2 |
+--------+
$ elixir day24part2.exs
3979
Thoughts:
More complicated now, because we actually have to iterate all the black/white cells and their
neighbours. Calculating the grid extremities looks complicated due to the hexagonal properties.
However, this is very similar to Day 17 Part 2, so I will just adapt that solution for here too:
1. For all current black squares, check the neighbours to see what its next state should be.
- additionally keep track of which white squares we identified.
2. As white cells must have a black neighbour to be flipped, we know that it's fine to only
check white cells that are next to a black cell. So iterate the white cells we encountered
in step 1, and check their neighbours too.
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| Overall Thoughts |
+------------------+
Let another game of life. 3rd time this year? This one was a bit more interesting due to the
hexagonal nature, but part two was almost the same as Day 17. Maybe that's a good reflection
on my day 17 implementation, though.
