C++ 8ms, Beats %100 of others. Uses Vector. Easy to understand, not smart code :)
```\n    int calPoints(vector& ops) {\n        vector rounds;\n        int lastIndex=0;\n        \n        for(string str : ops){\n            if(isdigit(str[0]
```\n    int calPoints(vector<string>& ops) {\n        vector<int> rounds;\n        int lastIndex=0;\n        \n        for(string str : ops){\n            if(isdigit(str[0]) || str[0] == \'-\'){\n                rounds.push_back(std::stoi(str));\n            }\n            else if(str[0] == \'+\'){\n                rounds.push_back(rounds[lastIndex]+rounds[lastIndex-1]);\n            }\n            else if(str[0] == \'D\'){\n                rounds.push_back(2*rounds[lastIndex]);\n            }\n            else if(str[0] == \'C\'){\n                rounds.pop_back();\n            }\n            \n            lastIndex = rounds.size()-1;\n        }\n        \n        return accumulate(rounds.begin(), rounds.end(),0); // calculates sum of vector\n    }
['C']