103 lines
2.7 KiB
Elixir
103 lines
2.7 KiB
Elixir
defmodule AOC.Day16 do
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use AOC.Day, day: 16
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def parse_input(lines) do
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lines
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|> Enum.with_index()
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|> Enum.flat_map(fn {line, y} ->
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line
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|> String.to_charlist()
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|> Enum.with_index()
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|> Enum.map(fn {space, x} ->
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{{y, x}, space}
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end)
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end)
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|> Enum.into(%{})
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end
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def new_location({y, x}, :north), do: {y - 1, x}
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def new_location({y, x}, :east), do: {y, x + 1}
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def new_location({y, x}, :south), do: {y + 1, x}
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def new_location({y, x}, :west), do: {y, x - 1}
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def new_directions(:north, ?\\), do: [:west]
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def new_directions(:north, ?/), do: [:east]
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def new_directions(:north, ?-), do: [:east, :west]
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def new_directions(:east, ?\\), do: [:south]
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def new_directions(:east, ?/), do: [:north]
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def new_directions(:east, ?|), do: [:south, :north]
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def new_directions(:south, ?\\), do: [:east]
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def new_directions(:south, ?/), do: [:west]
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def new_directions(:south, ?-), do: [:east, :west]
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def new_directions(:west, ?\\), do: [:north]
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def new_directions(:west, ?/), do: [:south]
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def new_directions(:west, ?|), do: [:south, :north]
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def new_directions(direction, _), do: [direction]
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def simulate_laser(grid, location, direction) do
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case :ets.lookup(:laser_memo, {location, direction}) do
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[] ->
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:ets.insert_new(:laser_memo, {{location, direction}, true})
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new_location = new_location(location, direction)
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case Map.fetch(grid, new_location) do
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{:ok, symbol} ->
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new_directions(direction, symbol)
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|> Enum.each(&simulate_laser(grid, new_location, &1))
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:error ->
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:ok
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end
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_ ->
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:ok
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end
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end
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def count_energized(grid, start_location, direction) do
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:ets.new(:laser_memo, [:named_table])
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simulate_laser(grid, start_location, direction)
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count =
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:ets.tab2list(:laser_memo)
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|> Enum.map(&elem(&1, 0))
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|> Enum.map(&elem(&1, 0))
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|> Enum.uniq()
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|> Enum.count()
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:ets.delete(:laser_memo)
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count - 1
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end
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def part1(grid) do
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count_energized(grid, {0, -1}, :east)
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end
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def part2(grid) do
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max_x =
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grid
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|> Enum.map(&elem(&1, 0))
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|> Enum.map(&elem(&1, 1))
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|> Enum.max()
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max_y =
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grid
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|> Enum.map(&elem(&1, 0))
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|> Enum.map(&elem(&1, 0))
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|> Enum.max()
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[
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Enum.map(0..max_x, fn x -> {{-1, x}, :south} end),
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Enum.map(0..max_x, fn x -> {{max_y + 1, x}, :north} end),
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Enum.map(0..max_y, fn y -> {{y, -1}, :east} end),
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Enum.map(0..max_y, fn y -> {{y, max_x + 1}, :west} end)
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]
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|> List.flatten()
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|> Enum.map(fn {position, direction} ->
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count_energized(grid, position, direction)
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end)
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|> Enum.max()
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end
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end
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