72 lines
1.8 KiB
Elixir
72 lines
1.8 KiB
Elixir
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defmodule AOC.Day15 do
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use AOC.Day, day: 15
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def parse_input(lines) do
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lines
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|> hd()
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|> String.split(",")
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end
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def part1(init_seq) do
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init_seq
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|> Enum.map(&String.to_charlist/1)
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|> Enum.map(&hash/1)
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|> Enum.sum()
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end
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def part2(init_seq) do
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init_seq
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|> Enum.map(fn step ->
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if String.contains?(step, "=") do
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[label, focal_length] = String.split(step, "=")
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{:add, String.to_charlist(label), String.to_integer(focal_length)}
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else
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label = step |> String.trim_trailing("-") |> String.to_charlist()
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{:remove, label}
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end
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end)
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|> Enum.reduce(%{}, fn
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{:remove, label}, acc ->
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box_number = hash(label)
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case Map.fetch(acc, box_number) do
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{:ok, lenses} ->
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%{acc | box_number => Enum.reject(lenses, &(elem(&1, 0) == label))}
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:error ->
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acc
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end
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{:add, label, focal_length}, acc ->
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box_number = hash(label)
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case Map.fetch(acc, box_number) do
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{:ok, lenses} ->
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case Enum.find_index(lenses, &(elem(&1, 0) == label)) do
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nil ->
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%{acc | box_number => [{label, focal_length} | lenses]}
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index ->
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%{acc | box_number => List.replace_at(lenses, index, {label, focal_length})}
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end
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:error ->
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Map.put(acc, box_number, [{label, focal_length}])
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end
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end)
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|> Enum.flat_map(fn {box_number, lenses} ->
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lenses
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|> Enum.reverse()
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|> Enum.with_index()
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|> Enum.map(fn {{_label, focal_length}, index} ->
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(box_number + 1) * (index + 1) * focal_length
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end)
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end)
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|> Enum.sum()
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end
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def hash(step), do: hash(step, 0)
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def hash([], acc), do: acc
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def hash([hd | tl], acc), do: hash(tl, rem(17 * (hd + acc), 256))
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end
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