92 lines
2.3 KiB
Elixir
92 lines
2.3 KiB
Elixir
defmodule Star do
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defstruct [:pos_x, :pos_y, :vel_x, :vel_y]
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def move_all(stars, secs) do
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Enum.map(stars, &move(&1, secs))
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end
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def move(star, secs) do
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%Star{star | pos_x: star.pos_x + star.vel_x * secs, pos_y: star.pos_y + star.vel_y * secs}
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end
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end
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defmodule Day10 do
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@input_pattern ~r/=< ?(-?\d+), ?(-?\d+)>.*=< ?(-?\d+), ?(-?\d+)>/
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def parse_line(line) do
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[pos_x, pos_y, v_x, v_y] =
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Regex.run(@input_pattern, line, capture: :all_but_first)
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|> Enum.map(&String.to_integer/1)
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%Star{pos_x: pos_x, pos_y: pos_y, vel_x: v_x, vel_y: v_y}
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end
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def init do
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File.stream!("input")
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|> Enum.map(&parse_line/1)
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end
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# Start with the first star, then compare all the others to find the extremities
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def bounding_box([%Star{pos_x: x, pos_y: y} | _] = stars) do
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Enum.reduce(stars, {x, y, x, y}, fn star, {min_x, min_y, max_x, max_y} ->
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{
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min(star.pos_x, min_x),
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min(star.pos_y, min_y),
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max(star.pos_x, max_x),
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max(star.pos_y, max_y)
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}
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end)
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end
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def draw(stars) do
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starfield = MapSet.new(stars, fn star -> {star.pos_x, star.pos_y} end)
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{min_x, min_y, max_x, max_y} = bounding_box(stars)
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grid =
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for y <- min_y..max_y, x <- min_x..max_x do
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eol = if x === max_x, do: "\n", else: ""
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char = if MapSet.member?(starfield, {x, y}), do: "#", else: " "
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char <> eol
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end
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Enum.join(grid)
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end
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def aligned?(stars) do
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starfield = MapSet.new(stars, fn star -> {star.pos_x, star.pos_y} end)
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Enum.all?(stars, &aligned?(&1, starfield))
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end
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def aligned?(star, starfield) do
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neighbours = [
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{star.pos_x - 1, star.pos_y - 1},
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{star.pos_x - 1, star.pos_y},
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{star.pos_x - 1, star.pos_y + 1},
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{star.pos_x, star.pos_y - 1},
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{star.pos_x, star.pos_y + 1},
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{star.pos_x + 1, star.pos_y - 1},
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{star.pos_x + 1, star.pos_y},
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{star.pos_x + 1, star.pos_y + 1}
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]
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Enum.any?(neighbours, &MapSet.member?(starfield, &1))
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end
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def wait_for_alignment(stars, count) do
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if aligned?(stars) do
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{stars, count}
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else
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stars |> Star.move_all(1) |> wait_for_alignment(count + 1)
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end
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end
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def go do
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{stars, count} = init() |> wait_for_alignment(0)
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IO.puts(draw(stars))
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IO.puts("#{count} seconds")
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end
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end
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Day10.go()
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