challenge.rb

def split_num(num)
  ("%04d" % num).split('').map(&:to_i)
end

def split_num_f(num)
  split_num(num).map(&:to_f)
end

def twined(nums, symbols)
  nums.zip(symbols).flatten.compact.map(&:to_s).join('')
end

S = [:+, :-, :*, :/].repeated_permutation(3)
def check(num)
  sp = split_num_f(num)
  return if sp.any?(&:zero?) || sp.uniq.count!=4

  S.map.select do |symbols|
    eval(twined(sp, symbols))==10
  end
end

r = 10_000.times.map { |num|
  c = check(num)
  unless c.nil? || c.empty?
    c.map{|cc| twined(split_num(num), cc)}
  end
}.flatten.compact

p r
p"---"
p r.length

ありがとう！参考にやってみます。