regexp_arithmetic.rb

def sum_reg(a, b, fallback = nil)
  fragments = (0..18).map do |sum|
    ".*\\k<#{a}>.{#{sum/2+5}}_.{#{sum-sum/2+5}}\\k<#{b}>.*-.{#{sum%10}}"
  end
  fragments << ".*-.{#{fallback}}" if fallback
  "(?:#{fragments.join('|')})"
end

S = '9876543210___________0123456789-0123456789'

reg = /^((?=.*(\3|0))(?=.*(\4|1))(?=#{sum_reg('2', '3')}(.))){5}/
puts(reg)
p reg.match S