【leetcode】Generate Parentheses

题目简述：

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

For example, given n = 3, a solution set is:

"((()))", "(()())", "(())()", "()(())", "()()()"

解题思路：

递归，用两个数组分别表示两种括号

class Solution:
def f(self,res,s,n,m):
if n == 0 and m == 0:
res.append(s)
return
if m > 0:
self.f(res,s+')',n,m-1)
if n > 0:
self.f(res,s+'(',n-1,m+1)

@param an integer

@return a list of string

def generateParenthesis(self, n):
s = ''
res = []
self.f(res,s,n,0)
return res