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56 lines
1.7 KiB
Elixir
56 lines
1.7 KiB
Elixir
1 month ago
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defmodule Day5 do
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def run do
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{rules, updates} = parseFile("data.txt")
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{validUpdates, invalidUpdates} = Enum.split_with(updates, &updateValid?(&1, rules))
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validMiddles = Enum.map(validUpdates, &middleDigit/1)
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IO.puts("Part 1: #{Enum.sum(validMiddles)}")
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# sort the invalid ones with a custom 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, fn first, second ->
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Enum.member?(rules, [first, second])
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end)
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end)
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invalidMiddles = Enum.map(invalidSorted, &middleDigit/1)
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IO.puts("Part 2: #{Enum.sum(invalidMiddles)}")
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end
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defp parseFile(file) do
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[topSection, bottomSection] = File.read!(file) |> String.split("\n\n")
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rules = String.split(topSection, "\n") |> Enum.map(fn l -> String.split(l, "|") end)
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updates =
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String.split(bottomSection, "\n")
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|> Enum.drop(-1)
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|> Enum.map(fn l -> String.split(l, ",") end)
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{rules, updates}
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end
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defp updateValid?(update, rules) do
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Enum.reduce_while(rules, true, fn [left, right], acc ->
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# if it doesn't contain both, or it does and they're in the right order
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if !(Enum.member?(update, left) and Enum.member?(update, right)) or
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Enum.find_index(update, &(&1 == left)) < Enum.find_index(update, &(&1 == right)) do
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# continue and try the next one
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{:cont, acc}
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else
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# otherwise halt the reduction, this update is invalid
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{:halt, false}
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end
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end)
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end
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defp middleDigit(update) do
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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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end
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Day5.run()
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