74 lines
2 KiB
Elixir
74 lines
2 KiB
Elixir
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defmodule Three do
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@dimension_parser ~r/\#(\d+)\s@\s(\d+),(\d+):\s(\d+)x(\d+)/
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def part1(input_stream) do
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input_stream
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|> Stream.map(&parse_dimensions/1)
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|> Stream.map(&points_in_square/1)
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|> Enum.to_list()
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|> Enum.reduce({MapSet.new([]), MapSet.new([])}, &intersecting_squares/2)
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|> elem(1)
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|> MapSet.to_list()
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|> length()
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end
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def parse_dimensions(str) do
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l = Regex.run(@dimension_parser, str)
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[id, x, y, w, h] = l |> tl() |> Enum.map(&String.to_integer/1)
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{id, x, y, w, h}
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end
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def points_in_square({_, x, y, w, h}) do
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x..(x + w - 1)
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|> Enum.reduce([], fn x, x_set ->
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y..(y + h - 1)
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|> Enum.reduce(x_set, fn y, xy_set ->
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[{x, y} | xy_set]
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end)
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end)
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end
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def intersecting_squares(square_set, {set, intersects}) do
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square_set
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|> Enum.reduce({set, intersects}, fn pos, {set, intersects} ->
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case MapSet.member?(set, pos) do
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true -> {set, MapSet.put(intersects, pos)}
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_ -> {MapSet.put(set, pos), intersects}
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end
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end)
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end
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def intersecting_squares2({id, square_set}, {set, intersects}) do
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square_set
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|> Enum.reduce({set, intersects}, fn pos, {set, intersects} ->
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case MapSet.member?(set, pos) do
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true -> {set, MapSet.put(intersects, pos)}
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_ -> {MapSet.put(set, pos), intersects}
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end
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end)
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end
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# parse input lines
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# for each set of dimensions, check each point in the square
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# if the point has been recorded already, remove both ids from the set
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def part2(input_stream) do
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square_data =
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input_stream
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|> Stream.map(&parse_dimensions/1)
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square_id_set =
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square_data
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|> Stream.map(&elem(&1, 0))
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|> Enum.to_list()
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|> MapSet.new()
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square_data
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|> Enum.map(&{elem(&1, 0), points_in_square(&1)})
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|> Enum.reduce({MapSet.new([]), square_id_set}, fn {id, points}, acc -> intersecting_squares2({id, points}, ))
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|> elem(1)
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|> MapSet.to_list()
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|> length()
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end
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end
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