50 lines
1 KiB
Elixir
50 lines
1 KiB
Elixir
defmodule SetTools do
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def combinations(_, 0) do
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[[]]
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end
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def combinations([], _) do
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[]
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end
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def combinations(list = [head | tail], size) do
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taken = Stream.map(combinations(tail, size - 1), fn subset -> [head | subset] end)
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left = combinations(tail, size)
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Stream.concat(taken, left)
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end
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end
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defmodule Day9 do
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defp read_input do
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Path.expand('input', Path.dirname(__ENV__.file))
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|> File.read!()
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end
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defp parse_lines(text) do
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text
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|> String.trim()
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|> String.split("\n")
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|> Enum.map(&String.to_integer/1)
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end
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def part1 do
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preamble_size = 25
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read_input()
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|> parse_lines()
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|> Stream.chunk_every(preamble_size + 1, 1, :discard)
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|> Enum.find(fn numbers ->
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preamble = Enum.take(numbers, preamble_size)
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next = List.last(numbers)
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has_match =
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SetTools.combinations(preamble, 2)
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|> Enum.any?(fn subset -> next == Enum.sum(subset) end)
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!has_match
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end)
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|> Enum.at(preamble_size)
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end
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end
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Day9.part1() |> IO.inspect()
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