[leetcode] Generate Parentheses

题目链接在此

醉了。easy难度的题刷得差不多了，找了几道medium的开始刷。发现不查下别人怎么写的，就很难下手。哎，修炼不够啊。决定leetcode上medium难度的缓一缓，先看看其他专业书。

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:

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

给出n，让你找出所有长度为2n的合法括号串。

代码和思路来自这位大神。里面还有非递归解法。

class Solution {public:vector<string> generateParenthesis(int n) {vector<string> v;generate(n, n, "", v);return v;}private:void generate(int leftNum, int rightNum, string s, vector<string> &result) {if (leftNum == 0 && rightNum == 0) {result.push_back(s);}if (leftNum>0) {generate(leftNum - 1, rightNum, s + '(', result);}if (rightNum>0 && leftNum<rightNum) {generate(leftNum, rightNum - 1, s + ')', result);}}};