Caleb Webber
bd9170e332
- avoid regex by using pattern matching - avoid looping through the acc on loop_receive by passing a count arg - remove the list acc for loop_receive by calculating lcm each time a message is received - convert from search to direct lookup for next instruction
65 lines
1.6 KiB
Elixir
65 lines
1.6 KiB
Elixir
defmodule Mix.Tasks.Day8 do
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use Mix.Task
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defp instruction_to_index("L"), do: 0
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defp instruction_to_index("R"), do: 1
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def walk(_, _, step, <<_::binary-size(2)>> <> "Z") do
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step
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end
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def walk(instructions, nodes, step, current_location) do
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index =
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instructions
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|> String.at(rem(step, String.length(instructions)))
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|> instruction_to_index()
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new_location = elem(Map.get(nodes, current_location), index)
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walk(instructions, nodes, step + 1, new_location)
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end
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def loop_receive(max_len, acc, count) do
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cond do
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count == max_len -> acc
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true -> receive do
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n -> loop_receive(max_len, MathUtil.lcm(acc, n), count + 1)
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end
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end
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end
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def solve(input, _) do
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[instructions, nodes] = input |> String.split("\n\n")
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nodes =
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for {key, steps} <-
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nodes
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|> String.split("\n")
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|> Stream.reject(&(&1 == ""))
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|> Stream.map(&String.split(String.trim(&1), " = "))
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|> Stream.map(fn [from, "(" <> <<a::binary-size(3)>> <> ", " <> <<b::binary-size(3)>> <> ")"] -> {from, {a,b}} end),
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into: %{} do
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{key, steps}
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end
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parent = self()
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pids = for entry <- nodes |> Map.keys() |> Stream.filter(&(&1 |> String.ends_with?("A"))) do
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spawn(fn ->
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send(parent,
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walk(
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instructions,
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nodes,
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0,
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entry
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)
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)
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end
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)
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end
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loop_receive(pids |> Enum.count(), 1, 0)
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end
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def run(_) do
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{_, puzzle_input} = File.read("./input/2023_8.txt")
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solve(puzzle_input, :part2) |> IO.puts()
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end
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end
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