DouKaku?

$KCODE = 'u'

PARENS = {
   '(' => ')',
   '{' => '}',
   '[' => ']',
}
RPARENS = PARENS.invert

def reverseString2_(str, acc, paren)
   if str.empty?
      [acc, []]
   else
      ch, *rest = str
      if PARENS.keys.include?(ch)
         str_, rest_ = reverseString2_(rest, [], ch)
         ch_ = if str_.first == ch
                  PARENS[ch]
               else
                  ch
               end
         reverseString2_(rest_, [str_, ch_, acc], paren)
      elsif paren and RPARENS.keys.include?(ch)
         ch_ = if ch == PARENS[paren]
                  RPARENS[ch]
               else
                  ch
               end
         [[ch_, acc], rest]
      else
         reverseString2_(rest, [ch, acc], paren)
      end
   end
end

def reverseString2(str)
   str_ = str.split(//)
   reversed, _ = reverseString2_(str_, [], nil)
   reversed.flatten.join
end

SAMPLE = [
   ["文字列(もじれつ)の反転(はんてん)",
    "(んてんは)転反の(つれじも)列字文"],
   ["対応[の{とれている(さまざまな)括弧}の(例)]です。",
    "。すで[(例)の{弧括(なまざまさ)るいてれと}の]応対"],
   ["これ(は(対応のとれていない)括弧がある例です。",
    "。すで例るあが弧括(いないてれとの応対)は(れこ"],
   ["これ(も{対応の)とれていない}括弧の例です。",
    "。すで例の弧括}いないてれと)の応対{も(れこ"],
]

def test_reverseString2
   SAMPLE.each do |input,expected|
      cond = if expected == (result = reverseString2(input)) then :OK else :NG end
      puts  "reverseString2(#{input.inspect})"
      puts  "     expected: #{expected.inspect}"
      print "       result: #{result.inspect}"
      puts  " ... #{cond}"
   end
end

if __FILE__ == $0 then test_reverseString2() end