Part 1
defmodule Aoc do
def find_all_index(l, a) do
l
|> Enum.with_index
|> Enum.reduce([], fn {x, i}, acc -> if x == a, do: [i | acc], else: acc end)
end
def loop([], _, results, count), do: {Enum.reverse(results), count}
def loop([head | tail], beams, results, count) do
{current, hits} = head
|> Enum.with_index(fn x, i ->
cond do
Enum.at(head, i + 1) == "^" and Enum.member?(beams, i + 1) -> {"|", 0}
Enum.at(head, i - 1) == "^" and Enum.member?(beams, i - 1) -> {"|", 0}
x == "^" and Enum.member?(beams, i) -> {"^", 1}
x == "." and Enum.member?(beams, i) -> {"|", 0}
true -> {x, 0}
end
end)
|> Enum.unzip
loop(tail, find_all_index(current, "|"), [current | results], count + Enum.sum(hits))
end
end
[start | lines] =
File.read!("ids.txt")
|> String.split("\n")
|> Enum.map(&String.graphemes/1)
start_index = Enum.find_index(start, &(&1 == "S"))
{results, count} = Aoc.loop(lines, [start_index], [], 0)
results
|> Enum.map(&Enum.join/1)
|> Enum.map(&IO.inspect/1)
IO.inspect(count)
No native find_all_index? (or all indexes)
