Remove Invalid Parentheses

Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results.

Note: The input string may contain letters other than the parentheses ( and ).

Examples:

"()())()" -> ["()()()", "(())()"]
"(a)())()" -> ["(a)()()", "(a())()"]
")(" -> [""]
class Solution {
public:
    vector<string> removeInvalidParentheses(string s) {
        set<string> temp;
        int n = s.length();

        int left_remove = 0;
        int right_remove = 0;
        for (int i = 0; i < n; i++)
        {
            if (s[i] == '(')
            {
                left_remove++;
            }
            else if (s[i] == ')')
            {
                if (left_remove > 0)
                {
                    left_remove--;
                }
                else
                {
                    right_remove++;
                }
            }
        }
        visit(s, n, 0, left_remove, right_remove, 0, 0, "", temp);

        vector<string> result(temp.begin(), temp.end());

        return result;
    }
private:
    void visit(string &s, int n, int pos, int left_remove, int right_remove, 
           int left_count, int right_count, string buf, set<string> &temp)
    {
        if (n == pos)
        {
            if (left_remove == 0 && right_remove == 0)
            {
                temp.insert(buf);
            }
            return;
        }

        if (s[pos] == '(')
        {
            if (left_remove > 0)
            {
                visit(s, n, pos+1, left_remove-1, right_remove, left_count, right_count, buf, temp);
            }
            visit(s, n, pos+1, left_remove, right_remove, left_count+1, right_count, buf+s[pos], temp);
        }
        else if (s[pos] == ')')
        {
            if (right_remove > 0)
            {
                visit(s, n, pos+1, left_remove, right_remove-1, left_count, right_count, buf, temp);
            }
            if (left_count <= right_count)
            {
                return;
            }
            visit(s, n, pos+1, left_remove, right_remove, left_count, right_count+1, buf+s[pos], temp);
        }
        else
        {
            visit(s, n, pos+1, left_remove, right_remove, left_count, right_count, buf+s[pos], temp);
        }
    }
};