题目

basic-calculator-ii

算法

* 直接模拟

代码

class Solution {
public:
    int calculate(string s) {
        int res = 0, d = 0;
        char sign = '+';
        stack<int> nums;
        for (int i = 0; i < s.size(); ++i) {
            if (s[i] >= '0') {
                d = d * 10 + s[i] - '0';
            }
            if ((s[i] < '0' && s[i] != ' ') || i == s.size() - 1) {
                if (sign == '+') nums.push(d);
                if (sign == '-') nums.push(-d);
                if (sign == '*' || sign == '/') {
                    int tmp = sign == '*' ? nums.top() * d : nums.top() / d;
                    nums.pop();
                    nums.push(tmp);
                }
                sign = s[i];
                d = 0;
            } 
        }
        while (!nums.empty()) {
            res += nums.top();
            nums.pop();
        }
        return res;
    }
};