aoc2017-day15-2-elx

defmodule Main do
    def generate(current, factor, modulus, scale) do
        next = rem(current * factor, modulus)
        case rem(next, scale) do
            0 -> next
            _ -> generate(next,factor,modulus,scale)
        end
    end
    
    def stream_generate(start, factor, modulus, scale) do
        first = generate(start, factor, modulus, scale)
        Stream.iterate(first,
            &(generate(&1, factor, modulus, scale)))
    end
end

use Bitwise
Stream.zip(
    Main.stream_generate(618, 16807, 2147483647, 4),
    Main.stream_generate(814, 48271, 2147483647, 8))
|> Stream.map(fn {x, y} -> (x &&& 0xFFFF) == (y &&& 0xFFFF) end)
|> Stream.map(fn match -> if match, do: 1, else: 0 end)
|> Stream.take(5000000)
|> Enum.sum
|> IO.puts