count = { 0 => 1 }
acc = 0
changes = File.read("day1").split("\n")
  .select { |it| !it.empty? } 
  .map(&.to_i)

while true
  changes.each do |i|
    acc += i
    old_count = count[acc]? || 0
    new_count = old_count + 1
    count[acc] = new_count

    if new_count == 2
      puts acc
      exit
    end
  end
end