Skip to content

Instantly share code, notes, and snippets.

@sasa1977
Last active December 5, 2018 15:10
Show Gist options
  • Save sasa1977/d70f0986bf72bb94048d37843d11b4a4 to your computer and use it in GitHub Desktop.
Save sasa1977/d70f0986bf72bb94048d37843d11b4a4 to your computer and use it in GitHub Desktop.
defmodule Day5 do
def part1(), do: polymer() |> react() |> polymer_size()
def part2() do
polymer()
|> unique_units()
|> Stream.map(&remove_unit(polymer(), &1))
|> Stream.map(&react/1)
|> Stream.map(&polymer_size/1)
|> Enum.min()
end
defp unique_units(polymer) do
polymer
|> Stream.flat_map(&([&1] |> to_string() |> String.upcase() |> to_charlist()))
|> Stream.uniq()
end
defp remove_unit(polymer, unit), do: Enum.reject(polymer, &(&1 == unit or opposite_polarities?(&1, unit)))
defp react([]), do: []
defp react([a | rest]) do
case react(rest) do
[] -> [a]
[b | rest] -> react_pair(a, b) ++ rest
end
end
defp react_pair(a, b), do: if(opposite_polarities?(a, b), do: [], else: [a, b])
defp opposite_polarities?(a, b), do: abs(a - b) == ?a - ?A
defp polymer() do
"input.txt"
|> File.read!()
|> to_charlist()
|> Enum.reject(&(&1 == ?\n))
end
defp polymer_size(polymer), do: length(polymer)
end
Day5.part1() |> IO.inspect()
Day5.part2() |> IO.inspect()
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment