给你一个由数字和运算符组成的字符串 expression ，按不同优先级组合数字和运算符，计算并返回所有可能组合的结果。你可以 按任意顺序 返回答案。

生成的测试用例满足其对应输出值符合 32 位整数范围，不同结果的数量不超过 104 。

示例 1：

输入：expression = "2-1-1"
输出：[0,2]
解释：
((2-1)-1) = 0
(2-(1-1)) = 2
示例 2：

输入：expression = "23-45"
输出：[-34,-14,-10,-10,10]
解释：
(2(3-(45))) = -34
((23)-(45)) = -14
((2(3-4))5) = -10
(2((3-4)5)) = -10
(((23)-4)5) = 10

class Solution {

    public List<Integer> cal2(String[] arr) {
        if (arr.length == 1) {
            return Arrays.asList(Integer.parseInt(arr[0]));
        }
        if (arr.length == 0) {
            return new ArrayList<>();
        }
        List<Integer> res = new ArrayList<>();
        for (int i = 0; i <= arr.length-2; i++) {
            if (arr[i].equals("+") || arr[i].equals("-") || arr[i].equals("*")) {
                continue;
            } else {
                List<Integer> left = cal2(Arrays.copyOfRange(arr, 0, i+1));
                List<Integer> right = cal2(Arrays.copyOfRange(arr, i+2, arr.length));
                for (int j = 0; j < left.size(); j++) {
                    for (int k = 0; k < right.size(); k++) {
                        if (arr[i+1].equals("+")) {
                            res.add(left.get(j) + right.get(k));
                        } else if (arr[i+1].equals("-")) {
                            res.add(left.get(j) - right.get(k));
                        } else if (arr[i+1].equals("*")) {
                            res.add(left.get(j) * right.get(k));
                        }
                    }
                }
            }
        }
        return res;
    }
    public List<Integer> diffWaysToCompute(String expression) {
        List<String> list = new ArrayList<>();
        String curStr = "";
        for (int i = 0; i < expression.length(); i++) {
            if (Character.isDigit(expression.charAt(i))) {
                curStr += String.valueOf(expression.charAt(i));
            } else {
                list.add(curStr);
                list.add(String.valueOf(expression.charAt(i)));
                curStr = "";
            }
        }
        list.add(curStr);
        String[] str = new String[list.size()];
        for (int i = 0; i < list.size(); i++) {
            str[i] = list.get(i);
        }
        List<Integer> res = cal2(str);
        return res;
    }
}