Java 1 ms, faster than 100.00%
Straight forward solution using arrays. \n\n    public int calPoints(String[] ops) {\n        int[] score = new int[ops.length];\n        int ind = -1, sum = 0;
Straight forward solution using arrays. \n\n    public int calPoints(String[] ops) {\n        int[] score = new int[ops.length];\n        int ind = -1, sum = 0;\n        \n        for(String s : ops){\n            if(s.equals("C")){\n                sum -= score[ind];\n                score[ind] = 0;\n                ind--;\n            }else if(s.equals("D")){\n                sum += score[ind]*2;\n                ind++;\n                score[ind] = score[ind-1]*2;                \n            }else if(s.equals("+")){\n                ind++;\n                score[ind] = score[ind-1] + score[ind-2];\n                sum += score[ind];\n            }else{\n                ind++;\n                score[ind] = Integer.parseInt(s);\n                sum += score[ind];\n            }\n            \n        }\n        return sum;\n    }
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