103 lines
2.1 KiB
Elixir
103 lines
2.1 KiB
Elixir
defmodule Day11Part2 do
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def run do
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File.read!("input")
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|> String.split("\n", trim: true)
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|> Enum.map(&String.to_charlist/1)
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|> parse_seat_plan()
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|> run_until_stable()
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|> count_occupied()
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|> IO.inspect()
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end
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def run_until_stable(seats) do
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new_seats = tick(seats)
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if new_seats == seats do
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seats
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else
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run_until_stable(new_seats)
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end
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end
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def tick(seats) do
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Map.new(seats, fn {{x, y}, old_seat} -> toggle(old_seat, x, y, seats) end)
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end
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def toggle(:empty, x, y, seats) do
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new_value =
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if occupied_visible(x, y, seats) == 0 do
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:occupied
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else
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:empty
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end
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{{x, y}, new_value}
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end
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def toggle(:occupied, x, y, seats) do
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new_value =
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if occupied_visible(x, y, seats) >= 5 do
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:empty
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else
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:occupied
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end
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{{x, y}, new_value}
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end
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def toggle(:floor, x, y, _), do: {{x, y}, :floor}
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def occupied_visible(x, y, seats) do
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directions = [
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{-1, -1},
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{-1, 0},
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{-1, +1},
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{0, -1},
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{0, +1},
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{+1, -1},
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{+1, 0},
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{+1, +1}
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]
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Enum.count(directions, fn {vx, vy} -> check_visible_in_direction(x, y, vx, vy, 1, seats) end)
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end
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def count_occupied(seats) do
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Enum.count(seats, &match?({_, :occupied}, &1))
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end
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def check_visible_in_direction(x, y, vx, vy, distance, seats) do
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next = seats[{x + vx * distance, y + vy * distance}]
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case next do
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nil -> false
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:empty -> false
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:occupied -> true
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:floor -> check_visible_in_direction(x, y, vx, vy, distance + 1, seats)
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end
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end
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def parse_seat_plan(input) do
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{_, seats} =
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Enum.reduce(input, {0, %{}}, fn row, {y, seats} ->
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{_, seats} =
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Enum.reduce(row, {0, seats}, fn seat, {x, seats} ->
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seat =
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case seat do
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?L -> :empty
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?. -> :floor
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?# -> :occupied
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end
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{x + 1, Map.put(seats, {x, y}, seat)}
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end)
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{y + 1, seats}
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end)
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seats
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end
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end
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Day11Part2.run()
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