227. 基本计算器 II

227. 基本计算器 II

每次把乘除运算放到一起算，遇到+-或i==n-1的时候算入res，并把curRes清零

class Solution {
public:
    int calculate(string s) {
        long res = 0, curRes = 0, num = 0, n = s.size();
        char op = '+';
        for (int i = 0; i < n; ++i) {
            char c = s[i];
            if (c >= '0' && c <= '9') {
                num = num * 10 +c - '0';
            }
            if (c == '+' || c == '-' || c == '*' || c == '/' || i == n - 1) {
                switch (op) {
                    case '+': curRes += num; break;
                    case '-': curRes -= num; break;
                    case '*': curRes *= num; break;
                    case '/': curRes /= num; break;
                }
                if (c == '+' || c == '-' || i == n - 1) {
                    res += curRes;
                    curRes = 0;
                }
                op = c;
                num = 0;
            } 
        }
        return res;
    }
};