Aurélien Geron
48 lines
1.5 KiB
Elixir
48 lines
1.5 KiB
Elixir
defmodule Aoc2024.Day05 do
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def parse(input) do
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[rules_raw, updates_raw] = input |> String.trim() |> String.split("\n\n")
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rules = Aoc2024.Utils.parse_rows_of_integers(rules_raw, "|")
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updates = Aoc2024.Utils.parse_rows_of_integers(updates_raw, ",")
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{rules, updates}
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end
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defp sort([], _rules), do: %{was_sorted?: true, list: []}
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defp sort([head | tail], rules) do
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result =
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tail
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|> Enum.reduce(%{sorted?: true, revlist: [], previous: head}, fn elem, acc ->
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if rules |> Enum.member?([elem, acc.previous]) do
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%{sorted?: false, revlist: [elem | acc.revlist], previous: acc.previous}
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else
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%{sorted?: acc.sorted?, revlist: [acc.previous | acc.revlist], previous: elem}
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end
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end)
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partially_sorted = [result.previous | result.revlist] |> Enum.reverse()
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if result.sorted? do
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%{was_sorted?: true, list: partially_sorted}
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else
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%{was_sorted?: false, list: sort(partially_sorted, rules).list}
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end
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end
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def part1({rules, updates}) do
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updates
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|> Enum.filter(fn update -> sort(update, rules).was_sorted? end)
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|> Enum.map(fn update -> update |> Enum.at(length(update) |> div(2)) end)
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|> Enum.sum()
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end
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def part2({rules, updates}) do
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updates
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|> Enum.map(fn update -> sort(update, rules) end)
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|> Enum.filter(fn sort_result -> not sort_result.was_sorted? end)
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|> Enum.map(fn sort_result ->
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sort_result.list |> Enum.at(length(sort_result.list) |> div(2))
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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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