98 lines
2.7 KiB
Elixir
98 lines
2.7 KiB
Elixir
defmodule Day3 do
|
|
def part1(input) do
|
|
gamma_rating = find_rating(input, 0, :most, <<>>)
|
|
epsillon_rating = find_rating(input, 0, :least, <<>>)
|
|
gamma_rating * epsillon_rating
|
|
end
|
|
|
|
defp find_rating([value | _], _, _, bits) when bit_size(value) == bit_size(bits) do
|
|
<<rating::size(bit_size(bits))>> = bits
|
|
rating
|
|
end
|
|
|
|
defp find_rating(values, bits_seen, mode, acc) do
|
|
bit = find_common(values, bits_seen, mode)
|
|
find_rating(values, bits_seen + 1, mode, <<acc::bits-size(bits_seen), bit::1>>)
|
|
end
|
|
|
|
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
|
|
|
|
def input do
|
|
with [input_filename] <- System.argv(),
|
|
{:ok, input} <- File.read(input_filename) do
|
|
strings = String.split(input, "\n", trim: true)
|
|
length = byte_size(hd(strings))
|
|
Enum.map(strings, &<<String.to_integer(&1, 2)::size(length)>>)
|
|
else
|
|
_ -> :error
|
|
end
|
|
end
|
|
|
|
#######################
|
|
# HERE BE BOILERPLATE #
|
|
#######################
|
|
|
|
def run do
|
|
case input() do
|
|
:error -> print_usage()
|
|
input -> run_parts_with_timer(input)
|
|
end
|
|
end
|
|
|
|
defp run_parts_with_timer(input) do
|
|
run_with_timer(1, fn -> part1(input) end)
|
|
run_with_timer(2, fn -> part2(input) end)
|
|
end
|
|
|
|
defp run_with_timer(part, fun) do
|
|
{time, result} = :timer.tc(fun)
|
|
IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
|
|
IO.puts("#{result}\n")
|
|
end
|
|
|
|
defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
|
|
defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
|
|
defp format_time(μsec), do: "#{μsec / 1_000_000}s"
|
|
|
|
defp print_usage do
|
|
IO.puts("Usage: elixir dayREPLACE_ME.exs input_filename")
|
|
end
|
|
end
|
|
|
|
Day3.run()
|