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);       }   };