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44 lines
1.4 KiB
Elixir
44 lines
1.4 KiB
Elixir
defmodule Day5 do
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def run do
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{rules, updates} = parseFile("data.txt")
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{invalidUpdates, validUpdates} = Enum.split_with(updates, &updateInvalid?(&1, rules))
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IO.puts("Part 1: #{sumMiddles(validUpdates)}")
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# sort the invalid ones with a sorter that looks for [a, b] in the rules list. if [a, b] exists, sort a before b
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invalidSorted =
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Enum.map(invalidUpdates, fn update ->
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Enum.sort(update, &Enum.member?(rules, [&1, &2]))
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end)
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IO.puts("Part 2: #{sumMiddles(invalidSorted)}")
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end
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defp parseFile(file) do
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# split the file on the empty line, then map splitting on newlines on both sections
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[top, bottom] = File.read!(file) |> String.split("\n\n") |> Enum.map(&String.split(&1, "\n"))
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rules = top |> Enum.map(&String.split(&1, "|"))
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updates = bottom |> Enum.drop(-1) |> Enum.map(&String.split(&1, ","))
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{rules, updates}
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end
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defp updateInvalid?(update, rules) do
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Enum.find(rules, false, fn [left, right] ->
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# it is invalid if it contains both and they're in the wrong order
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Enum.member?(update, left) and Enum.member?(update, right) and
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Enum.find_index(update, &(&1 == left)) > Enum.find_index(update, &(&1 == right))
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end)
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end
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defp sumMiddles(updates) do
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Enum.map(updates, fn update ->
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middle = trunc(length(update) / 2)
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String.to_integer(Enum.at(update, middle))
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end)
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|> Enum.sum()
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end
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end
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Day5.run()
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