AdventOfCode/2022/day6.exs

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Elixir
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2022-12-06 11:29:19 +00:00
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()