107 lines
2.5 KiB
Elixir
107 lines
2.5 KiB
Elixir
defmodule Day13 do
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defmodule Paper do
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defstruct dots: MapSet.new(), instructions: []
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end
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def part1(paper) do
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folded = fold(paper)
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MapSet.size(folded.dots)
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end
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defp fold(%Paper{dots: dots, instructions: [{axis, pos} | rest]}) do
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dots =
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MapSet.new(dots, fn {x, y} ->
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cond do
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axis == "x" and x > pos -> {pos - (x - pos), y}
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axis == "y" and y > pos -> {x, pos - (y - pos)}
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true -> {x, y}
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end
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end)
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%Paper{dots: dots, instructions: rest}
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end
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def part2(paper) do
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paper
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|> fold_all
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|> draw
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end
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defp fold_all(%Paper{instructions: []} = paper), do: paper
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defp fold_all(%Paper{} = paper), do: paper |> fold |> fold_all
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defp draw(paper) do
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{max_x, max_y} =
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for {x, y} <- paper.dots, reduce: {0, 0} do
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{max_x, max_y} -> {max(x, max_x), max(y, max_y)}
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end
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for y <- 0..max_y do
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row =
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for x <- 0..max_x do
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if MapSet.member?(paper.dots, {x, y}), do: ?#, else: ?\s
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end
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# could Enum.join("\n") here, but I want to play with iolists
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[row | "\n"]
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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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[dots, instructions] = String.split(input, "\n\n")
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dots =
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dots
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|> String.split([",", "\n"])
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|> Enum.map(&String.to_integer/1)
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|> Enum.chunk_every(2)
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|> MapSet.new(fn [x, y] -> {x, y} end)
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instructions =
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instructions
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|> String.split("\n", trim: true)
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|> Enum.map(fn <<"fold along ", axis::binary-1, "=", pos::binary>> ->
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{axis, String.to_integer(pos)}
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end)
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%Paper{dots: dots, instructions: instructions}
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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 day13.exs input_filename")
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end
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end
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Day13.run()
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