150. Evaluate Reverse Polish Notation

遇到符號就pop最上面的兩個做運算, 做完再塞回去

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        stack<string> operators;
        stack<int> integers;
        for(auto s: tokens){
            if(s == "+" || s == "-" || s == "/" || s=="*"){
                int num2 = integers.top();
                integers.pop();
                int num1 = integers.top();
                integers.pop();
                int cur = 0;
                if(s == "+"){
                    cur = num1 + num2;
                }else if (s == "-"){
                    cur = num1 - num2;
                }else if (s == "*"){
                    cur = num1 * num2;
                }else{
                    cur = num1 / num2;
                }
                integers.push(cur);
            }else{
                integers.push(stoi(s));
            }
        }
        return integers.top();
        
    }
};