def move(num_disks, start=0, target=2, using=1)
  if num_disks == 1
   @towers[target] << @towers[start].pop
    puts "Move disk from #{tower_name(start)} to #{tower_name(target)} : #{@towers}"
  else
    move(num_disks-1, start, using, target)
    move(1,           start, target, using)
    move(num_disks-1, using, target, start)
  end
end

n = 10

@towers = [[*1..n].reverse, [], []]
puts "#{(2**n) - 1} moves"
move(n)