51 lines
1.5 KiB
Elixir
51 lines
1.5 KiB
Elixir
defmodule Day7Part1 do
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@bag_spec ~r/\A(\d) (\w+ \w+).*\z/
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def run do
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File.read!("input")
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|> input_to_tree()
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|> invert_tree()
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|> count_ancestors("shiny gold")
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|> IO.puts()
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end
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def count_ancestors(itree, name), do: count_ancestors([name], MapSet.new(), itree)
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def count_ancestors([], bags, _itree), do: Enum.count(bags)
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def count_ancestors([name | rest], bags, itree) do
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case Map.fetch(itree, name) do
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:error -> count_ancestors(rest, bags, itree)
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{:ok, names} -> count_ancestors(names ++ rest, MapSet.union(bags, MapSet.new(names)), itree)
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end
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end
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# %{"shiny gold" => ["pale magenta", "striped tomato", ...]}
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def invert_tree(tree) do
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Enum.reduce(tree, %{}, fn {parent, children}, inverted_tree ->
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Enum.reduce(children, inverted_tree, fn {_n, child}, inverted_tree ->
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Map.update(inverted_tree, child, [parent], &[parent | &1])
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end)
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end)
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end
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# %{"shiny gold" => [{5, "pale brown"}, {2, "light red"}, {3, "drab lime"}]}
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def input_to_tree(input) do
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input
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|> String.split(".\n", trim: true)
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|> Enum.map(&String.split(&1, " bags contain "))
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|> Map.new(fn [parent, child_spec] -> {parent, parse_children(child_spec)} end)
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end
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def parse_children("no other bags"), do: []
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def parse_children(child_spec) do
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child_spec
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|> String.split(", ")
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|> Enum.map(&Regex.run(@bag_spec, &1, capture: :all_but_first))
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|> Enum.map(fn [count, type] -> {String.to_integer(count), type} end)
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end
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end
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Day7Part1.run()
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