module Enumerable

# File lib/jabara_group.rb, line 4
def jabara(n)
  raise ArgumentError.new('should be positive') if n <= 0
  return [dup] if n == 1

  index, direction = 0, 1
  each_with_object(Array.new(n) { [] }) do |e, groups|
    groups[index] << e

    case [index, direction]
    when [0, -1]
      direction = 0
    when [0, 0]
      direction = 1
    when [n - 1, 1]
      direction = 0
    when [n - 1, 0]
      direction = -1
    end
    index += direction
  end
end