23 leetcode - Generate Parentheses

#!/usr/bin/python# -*- coding: utf-8 -*-'''英文:Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.举例:given n = 3, a solution set is:[ "((()))",  "(()())",  "(())()",  "()(())",  "()()()"]'''class Solution(object):    def generateParenthesis(self, n):        """        :type n: int        :rtype: List[str]        """        if n < 1:          return []        result = []        tmp = ['('] * n * 2        left = n - 1        right = n        #第一个一定要为(        self.fun(tmp,result,left,right,1)        return result    def fun(self,tmp,result,left,right,index):        if left == 0 and right == 0:            result.append(''.join(tmp))        if left > 0:  #只要有(,就能放            tmp[index] = '('            self.fun(tmp,result,left - 1,right,index + 1)        if right > 0 and left < right:#(放了,)才能放,保证有一个(与之配对            if left == 0:  #小优化....                for i in range(right):                    tmp[index + i] = ')'                result.append(''.join(tmp))                return 0            tmp[index] = ')'            self.fun(tmp,result,left,right - 1,index + 1)if __name__ == "__main__":    s = Solution()    print s.generateParenthesis(3)