Yes, that is the reason. Since Erlang has no static types, it seems to be the only reasonable way to implement integers of arbitrary size.
Yes. No. You must mask with a mask of the correct size.
bjorng
Erlang Core Team
stevensonmt
unsek
Hey all, for those that want to watch a recap of Jose’s Day 3 stream, I edited something together in a shorter format: https://www.youtube.com/watch?v=SGQFAn4HtAI. I’ve done this for the first 2 days, and I’m also doing this for all the upcoming AoC days!
Each video has:
- Chapter markers for every single one so you could get a rough overview of the video and can skip to different parts if you wish.
- Twitch chat screenshots for additional context
- Jose’s planning process
- Errors Jose runs into with explanations (if available) on how to resolve it. He’s a good speaker so usually more context is provided.
Let me know what you want to be added/improved to make this easier to digest. I hope these will be useful!
2
adamu
I did it with bitstrings. But I wasn’t clever enough to notice you can skip calculating eplison.
Also, yes I know it’s 2022. Had submarine problems.
def part2(input) do
oxygen_generator_rating = find_rating2(input, 0, :most)
co2_scrubber_rating = find_rating2(input, 0, :least)
oxygen_generator_rating * co2_scrubber_rating
end
defp find_rating2([bits], _bits_seen, _mode) do
<<value::size(bit_size(bits))>> = bits
value
end
defp find_rating2(values, bits_seen, mode) do
bit = find_common(values, bits_seen, mode)
values
|> filter_by_bit(bits_seen, bit)
|> find_rating2(bits_seen + 1, mode)
end
defp find_common(values, bits_seen, mode) do
{zeros, ones} =
values
|> Enum.map(fn <<_::size(bits_seen), bit::1, _rest::bits>> -> bit end)
|> Enum.reduce({_zeros = 0, _ones = 0}, fn
0, {zeros, ones} -> {zeros + 1, ones}
1, {zeros, ones} -> {zeros, ones + 1}
end)
case mode do
:most -> if zeros <= ones, do: 1, else: 0
:least -> if zeros <= ones, do: 0, else: 1
end
end
defp filter_by_bit(values, num_prev_bits, bit) do
Enum.filter(values, &match?(<<_::size(num_prev_bits), ^bit::1, _rest::bits>>, &1))
end
https://git.adamu.jp/adam/AdventOfCode/src/branch/main/2021/day3.exs
0