Algorithms-Programming/Basic Calculator at master · exceptionhandle/Algorithms-Programming · GitHub

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class Solution {
public:
    int calculate(string s) {
        int num = 0, res = 0;
        int sign = 1;
        stack<int> opera;
        stack<int> intraRes;
        for(auto& x: s)
        {
            if(x == ' ') continue;
            if(isdigit(x))
            {
                num  = num*10 + x - '0';
                continue;
            }
            res += sign*num;
            num = 0;
            switch(x)
            {
                case '+':
                    sign = 1;
                    break;
                case '-':
                    sign = -1;
                    break;
                case '(':
                    opera.push(sign);
                    intraRes.push(res);
                    sign = 1;
                    res = 0;
                    num = 0;
                    break;
                case ')':
                    if(!intraRes.empty())
                        res = intraRes.top() + opera.top()*res,
                        num = 0,
                        sign = 1,
                        intraRes.pop(),
                        opera.pop();
                    break;
            }
        }
        return res + sign*num;
    }
};