80 lines
2.1 KiB
Elixir
80 lines
2.1 KiB
Elixir
#!/usr/bin/env elixir
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defmodule Day10 do
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def part1({grid, zeros}) do
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zeros
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|> Enum.map(fn point -> point |> score(grid, 0) |> Enum.uniq() |> Enum.count() end)
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|> Enum.sum()
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end
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def score(point, _grid, 9), do: [point]
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def score({x, y}, grid, height) do
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find_neighbours(x, y, height, grid)
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|> Enum.flat_map(fn {point, _} -> score(point, grid, height + 1) end)
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end
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def find_neighbours(x, y, height, grid) do
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next_height = height + 1
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grid
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|> Map.take([{x - 1, y}, {x + 1, y}, {x, y - 1}, {x, y + 1}])
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|> Enum.filter(&match?({_, ^next_height}, &1))
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end
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def part2({grid, zeros}) do
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zeros
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|> Enum.map(fn point -> point |> score(grid, 0) |> Enum.count() end)
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|> Enum.sum()
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end
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def input do
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with [input_filename] <- System.argv(),
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{:ok, input} <- File.read(input_filename) do
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{grid, zeros, _, _, _} =
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for <<char::binary-1 <- input>>, reduce: {%{}, [], 0, 0, 0} do
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{grid, zeros, x, max_x, y} ->
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case char do
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"\n" -> {grid, zeros, 0, x, y + 1}
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"0" -> {Map.put(grid, {x, y}, 0), [{x, y} | zeros], x + 1, max_x, y}
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char -> {Map.put(grid, {x, y}, String.to_integer(char)), zeros, x + 1, max_x, y}
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end
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end
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{grid, zeros}
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else
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_ -> :error
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end
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end
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#######################
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# HERE BE BOILERPLATE #
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#######################
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def run do
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case input() do
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:error -> print_usage()
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input -> run_parts_with_timer(input)
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end
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end
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defp run_parts_with_timer(input) do
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run_with_timer(1, fn -> part1(input) end)
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run_with_timer(2, fn -> part2(input) end)
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end
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defp run_with_timer(part, fun) do
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{time, result} = :timer.tc(fun)
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IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
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IO.puts("#{inspect(result)}\n")
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end
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defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
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defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
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defp format_time(μsec), do: "#{μsec / 1_000_000}s"
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defp print_usage do
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IO.puts("Usage: elixir day10.exs input_filename")
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end
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end
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Day10.run()
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