AdventOfCode/2020/elixir/day24/day24part1.exs

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Elixir
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2020-12-24 08:50:49 +00:00
defmodule Cell do
defstruct [:x, :y]
end
defmodule Day24Part1 do
def run do
File.read!("input")
|> String.split("\n", trim: true)
|> Enum.map(&parse_line/1)
|> Enum.map(&to_cell/1)
|> Enum.reduce(MapSet.new(), fn cell, black ->
if MapSet.member?(black, cell) do
MapSet.delete(black, cell)
else
MapSet.put(black, cell)
end
end)
|> Enum.count()
|> IO.puts()
end
def parse_line(str) do
str
|> String.graphemes()
|> Enum.chunk_while(
nil,
fn
"n", nil -> {:cont, :north}
"s", nil -> {:cont, :south}
"e", :north -> {:cont, :northeast, nil}
"e", :south -> {:cont, :southeast, nil}
"e", nil -> {:cont, :east, nil}
"w", :north -> {:cont, :northwest, nil}
"w", :south -> {:cont, :southwest, nil}
"w", nil -> {:cont, :west, nil}
end,
fn acc -> {:cont, acc} end
)
end
def to_cell(directions) do
Enum.reduce(directions, %Cell{x: 0, y: 0}, &move/2)
end
def move(:east, %Cell{x: x, y: y}), do: %Cell{x: x + 2, y: y}
def move(:west, %Cell{x: x, y: y}), do: %Cell{x: x - 2, y: y}
def move(:northeast, %Cell{x: x, y: y}), do: %Cell{x: x + 1, y: y + 1}
def move(:northwest, %Cell{x: x, y: y}), do: %Cell{x: x - 1, y: y + 1}
def move(:southeast, %Cell{x: x, y: y}), do: %Cell{x: x + 1, y: y - 1}
def move(:southwest, %Cell{x: x, y: y}), do: %Cell{x: x - 1, y: y - 1}
end
Day24Part1.run()