67 lines
1.5 KiB
Elixir
67 lines
1.5 KiB
Elixir
defmodule AOC.Day13 do
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use AOC.Day, day: 13
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alias AOC.Day13.Packet
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defmodule Packet do
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def compare({p1, p2}) do
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compare(p1, p2)
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end
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def compare([], []), do: :eq
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def compare([], _l), do: :lt
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def compare(_l, []), do: :gt
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def compare(x, l) when is_number(x) and is_list(l), do: compare([x], l)
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def compare(l, x) when is_number(x) and is_list(l), do: compare(l, [x])
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def compare([h1 | tl1], [h2 | tl2]) do
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case compare(h1, h2) do
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:eq -> compare(tl1, tl2)
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x -> x
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end
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end
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def compare(x, y) when x < y, do: :lt
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def compare(x, y) when x == y, do: :eq
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def compare(x, y) when x > y, do: :gt
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end
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def parse_input(lines) do
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lines
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|> Enum.chunk_by(&(&1 == ""))
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|> Enum.reject(&(&1 == [""]))
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|> Enum.map(fn [p1, p2] ->
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{parse_packet(p1), parse_packet(p2)}
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end)
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end
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def parse_packet(packet) do
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packet
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|> String.to_charlist()
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|> Code.string_to_quoted()
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|> elem(1)
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end
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def part1(pairs) do
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pairs
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|> Enum.map(&Packet.compare/1)
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|> Enum.with_index()
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|> Enum.filter(&(elem(&1, 0) == :lt))
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|> Enum.map(&elem(&1, 1))
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|> Enum.map(&Kernel.+(&1, 1))
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|> Enum.sum()
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end
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@divider_packets [[[2]], [[6]]]
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def part2(pairs) do
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pairs
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|> Enum.flat_map(fn {p1, p2} -> [p1, p2] end)
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|> Kernel.++(@divider_packets)
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|> Enum.sort(Packet)
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|> Enum.with_index()
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|> Enum.filter(&(elem(&1, 0) in @divider_packets))
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|> Enum.map(&elem(&1, 1))
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|> Enum.map(&Kernel.+(&1, 1))
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|> Enum.reduce(&Kernel.*/2)
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end
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end
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