AdventOfCode/2020/day14/day14part1.exs

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Elixir
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2020-12-14 11:57:38 +00:00
defmodule Day14Part1 do
use Bitwise
def run do
File.read!("input")
|> String.split("\n", trim: true)
|> Enum.map(&parse_command/1)
|> Enum.reduce({nil, %{}}, &execute/2)
|> sum_memory()
|> IO.inspect()
end
def execute({:mask, mask}, {_mask, mem}), do: {mask, mem}
def execute({:mem, addr, value}, {mask, mem}) do
masked_value = apply_mask(value, mask)
{mask, Map.put(mem, addr, masked_value)}
end
def sum_memory({_mask, mem}), do: Map.values(mem) |> Enum.sum()
def apply_mask(value, {andmask, ormask}), do: (value &&& andmask) ||| ormask
def parse_command("mask = " <> mask), do: {:mask, decode_mask(mask)}
def parse_command(mem_command) do
[addr, value] =
mem_command
|> String.split(["mem[", "] = "], trim: true)
|> Enum.map(&String.to_integer/1)
{:mem, addr, value}
end
def decode_mask(mask) when byte_size(mask) == 36 do
<<andmask::36>> = for <<bit::binary-1 <- mask>>, into: <<>>, do: andmask_bit(bit)
<<ormask::36>> = for <<bit::binary-1 <- mask>>, into: <<>>, do: ormask_bit(bit)
{andmask, ormask}
end
def andmask_bit("X"), do: <<1::1>>
def andmask_bit("1"), do: <<1::1>>
def andmask_bit("0"), do: <<0::1>>
def ormask_bit("X"), do: <<0::1>>
def ormask_bit("1"), do: <<1::1>>
def ormask_bit("0"), do: <<0::1>>
end
Day14Part1.run()