Method generateParenthesis

22. Generate Parentheses/Solution.cpp:46–51

backtracing The idea is intuitive. Use two integers to count the remaining left parenthesis (n) and the right parenthesis (m) to be added. At each function call add a left parenthesis if n > 0 and add a right parenthesis if m>0. Append the result and terminate recursive calls when both m and n are zero. */

        when both m and n are zero. 
    */
    vector<string> generateParenthesis(int n) {
        vector<string> res;
        string s = "";
        this->bt(res,n,n,s);
        return res;
    }
    
    void bt(vector<string> & v, int l, int r, string & str) {
        if (l == 0 and r == 0) {