AdventOfCode/2020/day5/day5part2-bitstring.exs

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Elixir
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defmodule Day5Part2 do
def run do
File.stream!("input")
|> Stream.map(&String.trim/1)
|> Stream.map(&seat_id/1)
|> Enum.sort()
|> find_seat()
|> IO.puts()
end
def find_seat([_ | next_seats] = seats) do
Stream.zip(seats, next_seats)
|> Enum.find(fn {seat, next} -> next - seat > 1 end)
|> elem(0)
|> Kernel.+(1)
end
def char_to_bit(c) when c in 'FL', do: <<0::1>>
def char_to_bit(c) when c in 'BR', do: <<1::1>>
def seat_id(boarding_pass) do
<<id::10>> = for <<char <- boarding_pass>>, into: <<>>, do: char_to_bit(char)
id
end
end
Day5Part2.run()