99 lines
2.7 KiB
Elixir
99 lines
2.7 KiB
Elixir
defmodule Day3 do
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def part1(input) do
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gamma_rating = find_rating(input, 0, :most, <<>>)
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epsillon_rating = find_rating(input, 0, :least, <<>>)
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gamma_rating * epsillon_rating
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end
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defp find_rating([value | _], _, _, bits) when bit_size(value) == bit_size(bits) do
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<<rating::size(bit_size(bits))>> = bits
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rating
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end
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defp find_rating(values, bits_seen, mode, acc) do
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bit = find_common(values, bits_seen, mode)
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find_rating(values, bits_seen + 1, mode, <<acc::bits-size(bits_seen), bit::1>>)
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end
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def part2(input) do
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oxygen_generator_rating = find_rating2(input, 0, :most)
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co2_scrubber_rating = find_rating2(input, 0, :least)
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oxygen_generator_rating * co2_scrubber_rating
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end
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defp find_rating2([bits], _bits_seen, _mode) do
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<<value::size(bit_size(bits))>> = bits
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value
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end
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defp find_rating2(values, bits_seen, mode) do
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bit = find_common(values, bits_seen, mode)
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values
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|> filter_by_bit(bits_seen, bit)
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|> find_rating2(bits_seen + 1, mode)
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end
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defp find_common(values, bits_seen, mode) do
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{zeros, ones} =
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values
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|> Enum.map(fn <<_::size(bits_seen), bit::1, _rest::bits>> -> bit end)
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|> Enum.reduce({_zeros = 0, _ones = 0}, fn
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0, {zeros, ones} -> {zeros + 1, ones}
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1, {zeros, ones} -> {zeros, ones + 1}
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end)
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case mode do
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:most -> if zeros <= ones, do: 1, else: 0
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:least -> if zeros <= ones, do: 0, else: 1
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end
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end
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defp filter_by_bit(values, num_prev_bits, bit) do
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Enum.filter(values, &match?(<<_::size(num_prev_bits), ^bit::1, _rest::bits>>, &1))
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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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strings = String.split(input, "\n", trim: true)
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length = byte_size(hd(strings))
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Enum.map(strings, &<<String.to_integer(&1, 2)::size(length)>>)
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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 dayREPLACE_ME.exs input_filename")
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end
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end
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Day3.run()
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