class Solution {
    public int calPoints(String[] ops) {
        List<Integer> records=new ArrayList<Integer>();
        int record=0;
        
        for(int i=0; i<ops.length; i++){
            if(ops[i].equals("+"))
                records.add(records.get(records.size()-2)+records.get(records.size()-1));
            else if(ops[i].equals("C"))
                records.remove(records.size()-1);
            else if(ops[i].equals("D"))
                records.add(2*records.get(records.size()-1));
            else
                records.add(Integer.parseInt(ops[i]));
        }
        
        for(int i:records)
            record+=i;
        
        return record;
    }
}