22.产生括号组

string dfs

题面

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses 
给定int n，代表n组括号，编码生成所有有效的括号组合（即符合括号嵌套规则）

样例

given n = 3, a solution set is: 
[ 
"((()))", 
"(()())", 
"(())()", 
"()(())", 
"()()()" 
]

思路

dfs

源码

1. class Solution {
2. public:
3. vector<string> generateParenthesis(int n) {
4. vector<string> res;
5. dfs("", 0, 0, res, n);
6. return res;
7. }
8. //dfs深搜
9. void dfs(string tmp, int l, int r, vector<string> &res, int n)
10. {
11. if(l == n && r == n)
12. {
13. res.push_back(tmp);
14. return ;
15. }
16. if(l < n)
17. dfs(tmp+"(", l+1, r, res, n);
18. if(l > r)
19. dfs(tmp+")", l, r+1, res, n);
20. }
21. };