89 lines
1.6 KiB
Elixir
89 lines
1.6 KiB
Elixir
import AOC
|
|
import AOC.Prelude
|
|
|
|
aoc 2024, 11 do
|
|
require Integer
|
|
|
|
def p1(input) do
|
|
input
|
|
|> read_stones()
|
|
|> count_stones_after_blink(25)
|
|
end
|
|
|
|
def p2(input) do
|
|
input
|
|
|> read_stones()
|
|
|> count_stones_after_blink(75)
|
|
end
|
|
|
|
##
|
|
|
|
defp count_stones_after_blink(stones, n) do
|
|
stones
|
|
|> Stream.iterate(&blink/1)
|
|
|> Enum.at(n)
|
|
|> count_stones()
|
|
end
|
|
|
|
defp blink(stones) do
|
|
for {stone, count} <- stones, reduce: stones do
|
|
stones ->
|
|
cond do
|
|
stone == 0 ->
|
|
stones
|
|
|> remove_stones(0, count)
|
|
|> add_stones(1, count)
|
|
|
|
even_digits?(stone) ->
|
|
{left, right} = split_stone(stone)
|
|
|
|
stones
|
|
|> remove_stones(stone, count)
|
|
|> add_stones(left, count)
|
|
|> add_stones(right, count)
|
|
|
|
true ->
|
|
stones
|
|
|> remove_stones(stone, count)
|
|
|> add_stones(stone * 2024, count)
|
|
end
|
|
end
|
|
end
|
|
|
|
defp even_digits?(num) do
|
|
num
|
|
|> Integer.digits()
|
|
|> Enum.count()
|
|
|> Integer.is_even()
|
|
end
|
|
|
|
defp split_stone(num) do
|
|
digits = Integer.digits(num)
|
|
|
|
{left, right} = Enum.split(digits, div(length(digits), 2))
|
|
|
|
{Integer.undigits(left), Integer.undigits(right)}
|
|
end
|
|
|
|
defp remove_stones(stones, num, count) do
|
|
Map.update(stones, num, 0, &(&1 - count))
|
|
end
|
|
|
|
defp add_stones(stones, num, count) do
|
|
Map.update(stones, num, count, &(&1 + count))
|
|
end
|
|
|
|
defp count_stones(stones) do
|
|
stones
|
|
|> Enum.map(&elem(&1, 1))
|
|
|> Enum.sum()
|
|
end
|
|
|
|
## input
|
|
|
|
defp read_stones(input) do
|
|
input
|
|
|> ints()
|
|
|> Enum.frequencies()
|
|
end
|
|
end
|