[Leetcode][Python]22: Generate Parentheses

# -*- coding: utf8 -*-‘‘‘__author__ = ‘[email protected]‘

22: Generate Parentheseshttps://oj.leetcode.com/problems/generate-parentheses/

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

===Comments by Dabay===递归。用left和right来记录剩余的左右括号数量。如果都不剩余了，把结果放入要返回的列表中。如果剩下的左括号比右括号多，说明不是合法的组合，返回。‘‘‘

class Solution:    # @param an integer    # @return a list of string    def generateParenthesis(self, n):        def generateParenthesis2(left, right, string, res):            if left == 0 and right == 0:                res.append(string)                return            if left > right:                return            if left > 0:                generateParenthesis2(left-1, right, string + "(", res)            if right > 0:                generateParenthesis2(left, right-1, string + ")", res)

        res = []        generateParenthesis2(n, n, "", res)        return res

def main():    sol = Solution()    print sol.generateParenthesis(4)

if __name__ == ‘__main__‘:    import time    start = time.clock()    main()    print "%s sec" % (time.clock() - start)