题解 | #括号生成#

struct MyTreeNode{
    MyTreeNode(string num){
        val = num;
    };
    string val;
    MyTreeNode *left=nullptr, *right=nullptr;
};

class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param n int整型 
     * @return string字符串vector
     */
    vector<string> generateParenthesis(int n) {
        // write code here
        int left_count = 0;
        int right_count = 0;
        int level = 1;
        string str = "";
        vector<string> res;
        dfs(left_count, right_count,level,n,str,res);
        return res;
    }

    void dfs(int left_count, int right_count, int level, int n, string str, vector<string> &res){
        if(level > 2*n){
            res.push_back(str);
            return;
        }else{
            if(left_count > right_count){
                dfs(left_count, right_count+1,level+1,n,str+")",res);
            }
            if(left_count < n){
                dfs(left_count+1, right_count,level+1,n,str+"(",res);
            }
        }
    }

};