96 lines
2.3 KiB
Elixir
96 lines
2.3 KiB
Elixir
defmodule Day10 do
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def part1(input) do
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input
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|> Enum.map(&parse_line(&1, []))
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|> Enum.filter(&match?({:corrupted, _}, &1))
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|> Enum.map(fn {:corrupted, char} -> score(char) end)
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|> Enum.sum()
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end
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defp parse_line(_, {:corrupted, char}), do: {:corrupted, char}
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defp parse_line("", stack), do: {:incomplete, stack}
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defp parse_line(<<char::utf8, rest::binary>>, []), do: parse_line(rest, [char])
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defp parse_line(<<char::utf8, next::binary>>, [prev | popped] = stack) do
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stack =
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case char do
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char when char in '([{<' -> [char | stack]
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?) when prev == ?( -> popped
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?] when prev == ?[ -> popped
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?} when prev == ?{ -> popped
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?> when prev == ?< -> popped
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char -> {:corrupted, char}
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end
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parse_line(next, stack)
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end
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defp score(?)), do: 3
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defp score(?]), do: 57
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defp score(?}), do: 1197
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defp score(?>), do: 25137
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def part2(input) do
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scores =
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input
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|> Enum.map(&parse_line(&1, []))
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|> Enum.filter(&match?({:incomplete, _}, &1))
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|> Enum.map(fn {_, chars} -> score2(chars) end)
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|> Enum.sort()
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Enum.at(scores, trunc(length(scores) / 2))
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end
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defp score2(chars) do
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for char <- chars, reduce: 0 do
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score -> score * 5 + points(char)
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end
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end
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defp points(?(), do: 1
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defp points(?[), do: 2
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defp points(?{), do: 3
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defp points(?<), do: 4
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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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String.split(input, "\n", trim: true)
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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 day10.exs input_filename")
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end
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end
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Day10.run()
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