def brackets(pairs, output='', open=0, close=0, arr = [])

arr << output if open == pairs and close == pairs

brackets pairs, output+'(', open+1, close, arr if open<pairs

brackets pairs, output+')', open, close+1, arr if close<open

arr

end

#test

p brackets(3) #["((()))", "(()())", "(())()", "()(())", "()()()"]