noob.rb

def can_close?(n, open, close)
  open > close
end

def can_open?(n, open, close)
  n > (open - close)
end

def par(res = '', n = 0, open = 0, close = 0)
  if n == 0
    puts res
  else
    if can_open?(n, open, close)
      par(res + '(', n - 1, open + 1, close)
    end

    if can_close?(n, open, close)
      par(res + ')', n - 1, open, close + 1)
    end
  end
end