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December 14, 2020 17:40
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Advent of Code 2020: Day 14
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defmodule Advent2020.Day14 do | |
defp parse_addr(<<"] = ", value::binary>>, acc), | |
do: {:mem, String.to_integer(acc), String.to_integer(value)} | |
defp parse_addr(<<d::binary-size(1), rest::binary>>, acc), do: parse_addr(rest, acc <> d) | |
def parse("mask = " <> mask), do: {:mask, mask} | |
def parse(<<"mem[", d::binary-size(1), rest::binary>>), do: parse_addr(rest, d) | |
def input do | |
Path.expand("day14.txt", :code.priv_dir(:advent_2020)) | |
|> File.stream!() | |
|> Stream.map(fn line -> parse(String.trim_trailing(line)) end) | |
end | |
defmodule PartOne do | |
use Bitwise | |
defp or_mask(mask), do: String.replace(mask, "X", "0") |> String.to_integer(2) | |
defp and_mask(mask), do: String.replace(mask, "X", "1") |> String.to_integer(2) | |
defp process({:mask, mask}, state), do: %{state | mask: {or_mask(mask), and_mask(mask)}} | |
defp process({:mem, addr, value}, %{mask: {or_mask, and_mask}, mem: mem} = state) do | |
%{state | mem: Map.put(mem, addr, (value ||| or_mask) &&& and_mask)} | |
end | |
def run(input) do | |
%{mem: mem} = Enum.reduce(input, %{mask: nil, mem: %{}}, &process/2) | |
Map.values(mem) |> Enum.sum() | |
end | |
end | |
defmodule PartTwo do | |
use Bitwise | |
defp or_mask(mask), do: String.replace(mask, "X", "0") |> String.to_integer(2) | |
defp and_mask(mask) do | |
String.replace(mask, "0", "1") | |
|> String.replace("X", "0") | |
|> String.to_integer(2) | |
end | |
defp bitmasks(mask) do | |
to_charlist(mask) | |
|> Enum.reverse() | |
|> Enum.reduce({1, []}, fn | |
?X, {bitmask, masks} -> {bitmask <<< 1, [bitmask | masks]} | |
_, {bitmask, masks} -> {bitmask <<< 1, masks} | |
end) | |
|> elem(1) | |
end | |
defp recur_bitmasks(addr, [], mem, value), do: Map.put(mem, addr, value) | |
defp recur_bitmasks(addr, [bitmask | bitmasks], mem, value) do | |
mem = recur_bitmasks(addr, bitmasks, mem, value) | |
recur_bitmasks(addr ||| bitmask, bitmasks, mem, value) | |
end | |
defp process({:mask, mask}, state), | |
do: %{state | mask: {or_mask(mask), and_mask(mask), bitmasks(mask)}} | |
defp process({:mem, addr, value}, %{mask: mask, mem: mem} = state) do | |
{or_mask, and_mask, bitmasks} = mask | |
addr = (addr ||| or_mask) &&& and_mask | |
%{state | mem: recur_bitmasks(addr, bitmasks, mem, value)} | |
end | |
def run(input) do | |
%{mem: mem} = Enum.reduce(input, %{mask: nil, mem: %{}}, &process/2) | |
Map.values(mem) |> Enum.sum() | |
end | |
end | |
end |
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