力扣227.基本计算器II

力扣227.基本计算器II

• 先算*/

  • 让栈里只剩下+

  • 最后求和即可

•   class Solution {
    public:
        int calculate(string s) {
            vector<int> st;
            char presign = '+';
            int num = 0;
            int n = s.size();
            for(int i=0;i<n;i++)
            {
                if(isdigit(s[i]))
                    num = num*10 + (s[i] - '0');
                if(!isdigit(s[i]) && s[i] != ' ' || i == n-1)
                {
                    if(presign == '+')
                        st.push_back(num);
                    else if(presign == '-')
                        st.push_back(-num);
                    else if(presign == '/')
                        st.back() /= num;
                    else
                        st.back() *= num;
                    presign = s[i];
                    num = 0;
                }
            }
            return accumulate(st.begin(),st.end(),0);
        }
    };