class MyNumber

# File lib/mynumber.rb, line 4
def self.corporate_number?(n)
  return false unless n.to_s =~ /^\d{13}$/

  digits = n.to_s.chars.map(&:to_i)
  check_digit = digits.pop
  sum = digits.map.with_index do |p, idx|
    # nが奇数のとき 1, nが偶数のとき 2
    q = (idx + 1).odd? ? 1 : 2
    p * q
  end.inject(0, :+)

  check_digit == (9 - sum % 9)
end

# File lib/mynumber.rb, line 18
def self.individual_number?(n)
  return false unless n.to_s =~ /^\d{12}$/

  digits = n.to_s.chars.map(&:to_i)
  check_digit = digits.pop
  remainder = digits.map.with_index do |p, idx|
    idx = 11 - idx
    # 1<=n<=6のとき n+1, 7<=ｎ<=11のとき n-5
    q = (idx <= 6) ? idx + 1 : idx - 5
    p * q
  end.inject(0, :+) % 11

  case remainder
  when 0, 1
    check_digit == 0
  else
    check_digit == (11 - remainder)
  end
end