73 lines
1.8 KiB
Elixir
73 lines
1.8 KiB
Elixir
defmodule Day6 do
|
|
@packet_marker_size 4
|
|
@message_marker_size 14
|
|
|
|
def part1(input) do
|
|
find_packet_marker(input)
|
|
end
|
|
|
|
defguardp all_different(a, b, c, d)
|
|
when a != b and a != c and a != d and b != c and b != d and c != d
|
|
|
|
defp find_packet_marker(buffer, seen \\ @packet_marker_size)
|
|
defp find_packet_marker([a, b, c, d | _rest], seen) when all_different(a, b, c, d), do: seen
|
|
defp find_packet_marker([_skip | rest], seen), do: find_packet_marker(rest, seen + 1)
|
|
|
|
def part2(input) do
|
|
find_message_marker(input)
|
|
end
|
|
|
|
defp find_message_marker([_skip | rest] = buffer, seen \\ @message_marker_size) do
|
|
window = Enum.take(buffer, @message_marker_size)
|
|
|
|
if Enum.uniq(window) == window do
|
|
seen
|
|
else
|
|
find_message_marker(rest, seen + 1)
|
|
end
|
|
end
|
|
|
|
def input do
|
|
with [input_filename] <- System.argv(),
|
|
{:ok, input} <- File.read(input_filename) do
|
|
input
|
|
|> String.trim()
|
|
|> String.codepoints()
|
|
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 day6.exs input_filename")
|
|
end
|
|
end
|
|
|
|
Day6.run()
|