AdventOfCode/2020/elixir/day10/day10part2.exs

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Elixir
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2020-12-10 15:28:41 +00:00
defmodule Day10Part2 do
def run do
File.read!("input")
|> String.split("\n", trim: true)
|> Enum.map(&String.to_integer/1)
|> count_arrangements()
|> IO.puts()
end
def count_arrangements(list), do: count_arrangements(%{0 => 1}, [0 | Enum.sort(list)])
def count_arrangements(arrs_to, [last]), do: arrs_to[last]
def count_arrangements(arrs_to, [current | rest]) do
rest
|> Enum.take(3)
|> count_reachable(current, arrs_to)
|> count_arrangements(rest)
end
def count_reachable([], _a, arrs_to), do: arrs_to
def count_reachable([b | rest], a, arrs_to) when b - a <= 3 do
arrs_to = Map.update(arrs_to, b, arrs_to[a], &(&1 + arrs_to[a]))
count_reachable(rest, a, arrs_to)
end
def count_reachable([_b | rest], a, arrs_to), do: count_reachable(rest, a, arrs_to)
end
Day10Part2.run()