LeetCode OJ：Generate Parentheses（括号生成）

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:

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

求出所有可能的括号组合，在dfs加上回溯条件，右括号数目不能超过左括号，还有就是左括号数最大不能超过n，代码如下：

 1 class Solution {
 2 public:
 3     vector<string> generateParenthesis(int n) {
 4         dfs(0,n*2,0,0,"");
 5         return ret;
 6     }
 7 
 8     void dfs(int dep, int maxDep, int left, int leftTotal, string curr){
 9         if(leftTotal*2 > maxDep)
10             return;
11         if(dep == maxDep){
12             ret.push_back(curr);
13             return;
14         }
15         for(int i = 0; i < 2; i++){
16             if(i == 0){
17                 dfs(dep+1, maxDep, left+1, leftTotal+1, curr+"(");
18             }else{
19                 if(left)
20                     dfs(dep+1, maxDep, left-1, leftTotal, curr+")");
21             }
22         }
23     }
24 private:
25     vector<string> ret;
26 };