73 lines
1.8 KiB
Elixir
73 lines
1.8 KiB
Elixir
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defmodule Day6 do
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@packet_marker_size 4
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@message_marker_size 14
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def part1(input) do
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find_packet_marker(input)
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end
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defguardp all_different(a, b, c, d)
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when a != b and a != c and a != d and b != c and b != d and c != d
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defp find_packet_marker(buffer, seen \\ @packet_marker_size)
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defp find_packet_marker([a, b, c, d | _rest], seen) when all_different(a, b, c, d), do: seen
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defp find_packet_marker([_skip | rest], seen), do: find_packet_marker(rest, seen + 1)
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def part2(input) do
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find_message_marker(input)
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end
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defp find_message_marker([_skip | rest] = buffer, seen \\ @message_marker_size) do
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window = Enum.take(buffer, @message_marker_size)
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if Enum.uniq(window) == window do
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seen
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else
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find_message_marker(rest, seen + 1)
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end
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end
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def input do
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with [input_filename] <- System.argv(),
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{:ok, input} <- File.read(input_filename) do
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input
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|> String.trim()
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|> String.codepoints()
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else
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_ -> :error
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end
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end
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#######################
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# HERE BE BOILERPLATE #
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#######################
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def run do
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case input() do
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:error -> print_usage()
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input -> run_parts_with_timer(input)
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end
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end
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defp run_parts_with_timer(input) do
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run_with_timer(1, fn -> part1(input) end)
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run_with_timer(2, fn -> part2(input) end)
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end
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defp run_with_timer(part, fun) do
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{time, result} = :timer.tc(fun)
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IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
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IO.puts("#{result}\n")
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end
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defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
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defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
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defp format_time(μsec), do: "#{μsec / 1_000_000}s"
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defp print_usage do
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IO.puts("Usage: elixir day6.exs input_filename")
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end
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end
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Day6.run()
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