4digits.rb

(0..9).to_a.repeated_combination(4).each do |fourDigits|
  ten = false
  first = false
  fourDigits.permutation.each do |a, b, c, d|
    ['+', '-', '*', '/'].repeated_permutation(3).each do |op1, op2, op3|
      term = "((#{a}.0#{op1}#{b}.0)#{op2}#{c}.0)#{op3}#{d}.0"
      if (eval(term) == 10.0 rescue false)
        ten = true
        break
      end

      term = "(#{a}.0#{op1}#{b}.0)#{op2}(#{c}.0#{op3}#{d}.0)"
      if (eval(term) == 10.0 rescue false)
        ten = true
        break
      end
    end
  end

  p fourDigits unless ten
end