AdventOfCode/2020/elixir/day5/day5part2.exs

40 lines
1,004 B
Elixir

defmodule Day5Part2 do
def run do
File.stream!("input")
|> 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 seat_id(boarding_pass) do
{row_spec, col_spec} = boarding_pass |> String.trim() |> String.to_charlist() |> Enum.split(7)
row =
Enum.reduce(row_spec, {0, 128}, fn
?F, {front, 2} -> front
?B, {front, 2} -> front + 1
?F, {front, count} -> {front, div(count, 2)}
?B, {front, count} -> {front + div(count, 2), div(count, 2)}
end)
col =
Enum.reduce(col_spec, {0, 8}, fn
?L, {left, 2} -> left
?R, {left, 2} -> left + 1
?L, {left, count} -> {left, div(count, 2)}
?R, {left, count} -> {left + div(count, 2), div(count, 2)}
end)
row * 8 + col
end
end
Day5Part2.run()