<p>Given a string <code>expression</code> of numbers and operators, return <em>all possible results from computing all the different possible ways to group numbers and operators</em>. You may return the answer in <strong>any order</strong>.</p>

<p>The test cases are generated such that the output values fit in a 32-bit integer and the number of different results does not exceed <code>10<sup>4</sup></code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> expression = &quot;2-1-1&quot;
<strong>Output:</strong> [0,2]
<strong>Explanation:</strong>
((2-1)-1) = 0 
(2-(1-1)) = 2
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> expression = &quot;2*3-4*5&quot;
<strong>Output:</strong> [-34,-14,-10,-10,10]
<strong>Explanation:</strong>
(2*(3-(4*5))) = -34 
((2*3)-(4*5)) = -14 
((2*(3-4))*5) = -10 
(2*((3-4)*5)) = -10 
(((2*3)-4)*5) = 10
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= expression.length &lt;= 20</code></li>
	<li><code>expression</code> consists of digits and the operator <code>&#39;+&#39;</code>, <code>&#39;-&#39;</code>, and <code>&#39;*&#39;</code>.</li>
	<li>All the integer values in the input expression are in the range <code>[0, 99]</code>.</li>
</ul>

class Solution {
public:
    vector<int> diffWaysToCompute(string expression) {
        vector<int> operands;
        vector<char> operators;
        int idx = 0;
        while (idx < expression.length()) {
            if ('0' <= expression[idx] && expression[idx] <= '9') {
                operands.push_back(read_int(expression, idx));
            } else if (expression[idx] == '+') {
                operators.push_back('+');
                idx++;
            } else if (expression[idx] == '*') {
                operators.push_back('*');
                idx++;
            } else if (expression[idx] == '-') {
                operators.push_back('-');
                idx++;
            } else {
                idx++;
            }
        }
        return diffWaysToCompute(operands, operators, 0, operands.size() - 1);
    }

    int read_int(string expression, int &idx) {
        int ans = 0;
        while (idx < expression.length() && expression[idx] >= '0' && expression[idx] <= '9') {
            ans *= 10;
            ans += expression[idx] - '0';
            idx++;
        }
        return ans;
    }

    vector<int> diffWaysToCompute(const vector<int> &operands, const vector<char> &operators, int start, int end) {
        if (start > end) return vector<int>();
        if (start == end) {
            return vector<int>(1, operands[start]);
        }
        vector<int> res;
        for (int i = start; i < end; i++) {
            vector<int> first = diffWaysToCompute(operands, operators, start, i);
            vector<int> second = diffWaysToCompute(operands, operators, i + 1, end);
            for (int f: first) {
                for (int s: second) {
                    res.push_back(evaluate(f, s, operators[i]));
                }
            }
        }
       return res;
    }

    int evaluate(int a, int b, char op) {
        switch (op) {
        case '+':
            return a + b;
        case '*':
            return a * b;
        case '-':
            return a - b;
        default:
            return 0;
        }
    }
};
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