92 lines
2 KiB
Elixir
92 lines
2 KiB
Elixir
defmodule TreeMap do
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def start_link(map_text) do
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Task.start_link(fn -> loop(parse(map_text)) end)
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end
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defp parse(text) do
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String.split(text, "\n", trim: true)
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|> Enum.with_index()
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|> Enum.reduce(%{grid: %{}, width: 0, height: 0}, fn {line, r}, map ->
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String.codepoints(line)
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|> Enum.with_index()
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|> Enum.reduce(map, fn {char, c}, map ->
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%{
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grid: Map.put(map.grid, {r, c}, char_to_content(char)),
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width: max(map.width, c + 1),
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height: max(map.height, r + 1)
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}
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end)
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end)
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end
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defp loop(map) do
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receive do
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{:get, {r, c}, caller} ->
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send(caller, Map.fetch(map.grid, wrap({r, c}, {map.width, map.height})))
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loop(map)
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end
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end
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defp wrap({r, c}, {w, _h}) do
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{r, rem(c, w)}
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end
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defp char_to_content(char) do
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case char do
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"." -> :open
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"#" -> :tree
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end
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end
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end
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defmodule Day3 do
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defp read_input do
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Path.expand('input', Path.dirname(__ENV__.file))
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|> File.read!()
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end
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defp content(tree_map, {r, c}) do
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send(tree_map, {:get, {r, c}, self()})
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receive do
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{:ok, content} -> content
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:error -> :error
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end
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end
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defp trees(tree_map, slope) do
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{dr, dc} = slope
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Stream.iterate({0, 0}, fn {r, c} -> {r + dr, c + dc} end)
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|> Enum.reduce_while(0, fn cell, tree_count ->
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case content(tree_map, cell) do
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:error -> {:halt, tree_count}
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:open -> {:cont, tree_count}
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:tree -> {:cont, tree_count + 1}
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end
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end)
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end
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def part1 do
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{:ok, tree_map} = TreeMap.start_link(read_input())
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trees(tree_map, {1, 3})
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end
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def part2 do
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{:ok, tree_map} = TreeMap.start_link(read_input())
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slopes = [
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{1, 1},
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{1, 3},
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{1, 5},
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{1, 7},
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{2, 1}
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]
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Enum.map(slopes, fn slope -> trees(tree_map, slope) end)
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|> Enum.reduce(1, fn x, prod -> x * prod end)
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end
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end
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Day3.part1() |> IO.inspect()
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Day3.part2() |> IO.inspect()
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