leetcode Generate Parentheses python

# 解题思路：列举出所有合法的括号匹配，使用dfs。如果左括号的数量大于右括号的数量的话，就不能产生合法的括号匹配
class Solution(object):
    def generateParenthesis(self, n):
        """
        :type n: int
        :rtype: List[str]
        """
        if n == 0:
            return []
        res = []
        self.recursion(n,n,'',res)
        return res
    def recursion(self,left,right,item,res):
        if right < left:
            return
        if left == 0 and right == 0:
            res.append(item)
        if left > 0:
            self.recursion(left-1,right,item+'(',res)
        if right > 0:
            self.recursion(left,right-1,item+')',res)

 @link http://www.cnblogs.com/zuoyuan/p/3779797.html