aoc/23/elixir/lib/days/day16.ex

104 lines
2.7 KiB
Elixir
Raw Normal View History

2023-12-17 23:42:06 +00:00
defmodule AOC.Day16 do
use AOC.Day, day: 16
def parse_input(lines) do
lines
|> Enum.with_index()
|> Enum.flat_map(fn {line, y} ->
line
|> String.to_charlist()
|> Enum.with_index()
|> Enum.map(fn {space, x} ->
{{y, x}, space}
end)
end)
|> Enum.into(%{})
end
def new_location({y, x}, :north), do: {y - 1, x}
def new_location({y, x}, :east), do: {y, x + 1}
def new_location({y, x}, :south), do: {y + 1, x}
def new_location({y, x}, :west), do: {y, x - 1}
def new_directions(:north, ?\\), do: [:west]
def new_directions(:north, ?/), do: [:east]
def new_directions(:north, ?-), do: [:east, :west]
def new_directions(:east, ?\\), do: [:south]
def new_directions(:east, ?/), do: [:north]
def new_directions(:east, ?|), do: [:south, :north]
def new_directions(:south, ?\\), do: [:east]
def new_directions(:south, ?/), do: [:west]
def new_directions(:south, ?-), do: [:east, :west]
def new_directions(:west, ?\\), do: [:north]
def new_directions(:west, ?/), do: [:south]
def new_directions(:west, ?|), do: [:south, :north]
def new_directions(direction, _), do: [direction]
def simulate_laser(grid, location, direction) do
case :ets.lookup(:laser_memo, {location, direction}) do
[] ->
:ets.insert_new(:laser_memo, {{location, direction}, true})
new_location = new_location(location, direction)
case Map.fetch(grid, new_location) do
{:ok, symbol} ->
new_directions(direction, symbol)
|> Enum.each(&simulate_laser(grid, new_location, &1))
:error ->
:ok
end
_ ->
:ok
end
end
def count_energized(grid, start_location, direction) do
:ets.new(:laser_memo, [:named_table])
simulate_laser(grid, start_location, direction)
count =
:ets.tab2list(:laser_memo)
|> Enum.map(&elem(&1, 0))
|> Enum.map(&elem(&1, 0))
|> Enum.uniq()
|> Enum.count()
:ets.delete(:laser_memo)
count - 1
end
def part1(grid) do
count_energized(grid, {0, -1}, :east)
end
def part2(grid) do
max_x =
grid
|> Enum.map(&elem(&1, 0))
|> Enum.map(&elem(&1, 1))
|> Enum.max()
max_y =
grid
|> Enum.map(&elem(&1, 0))
|> Enum.map(&elem(&1, 0))
|> Enum.max()
[
Enum.map(0..max_x, fn x -> {{-1, x}, :south} end),
Enum.map(0..max_x, fn x -> {{max_y + 1, x}, :north} end),
Enum.map(0..max_y, fn y -> {{y, -1}, :east} end),
Enum.map(0..max_y, fn y -> {{y, max_x + 1}, :west} end)
]
|> List.flatten()
|> Enum.map(fn {position, direction} ->
count_energized(grid, position, direction)
end)
|> Enum.max()
end
end