题解 | 逆波兰表达式求值

C++

class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param tokens string字符串vector
     * @return int整型
     */
    int evalRPN(vector<string>& tokens) {
        // write code here
        stack<int> s;
        for (auto& ch : tokens) {
            int t;
            if (ch == "+") {
                int a = s.top(); s.pop();
                int b = s.top(); s.pop();
                t = b + a;
            } else if (ch == "-") {
                int a = s.top(); s.pop();
                int b = s.top(); s.pop();
                t = b - a;
            } else if (ch == "*") {
                int a = s.top(); s.pop();
                int b = s.top(); s.pop();
                t = b * a;
            } else if (ch == "/") {
                int a = s.top(); s.pop();
                int b = s.top(); s.pop();
                t = b / a;
            }
            else t = stoi(ch); // string to int
            s.push(t);
        }
        return s.top();
    }
};