evaluate-reverse-polish-notati 计算逆波兰式的值

 1 class Solution {
 2 public:
 3     /**
 4      * 
 5      * @param tokens string字符串vector 
 6      * @return int整型
 7      */
 8     int evalRPN(vector<string>& tokens) {
 9         // write code here
10         stack<int> st;
11         for(auto token : tokens) {
12             if(token == "+" || token == "-" || token == "*" || token == "/"){
13                 int num_a = st.top();st.pop();
14                 int num_b = st.top();st.pop();
15                 if(token == "+" )
16                     st.push((num_b + num_a));
17                 if(token == "-" )
18                     st.push((num_b - num_a));
19                 if(token == "*" )
20                     st.push((num_b * num_a));
21                 if(token == "/" )
22                     st.push((num_b / num_a));
23             }
24             else{
25                 stringstream strs;
26                 strs << token;
27                 int temp;
28                 strs >> temp;
29                 st.push(temp);
30             }
31         } 
32         return st.top();
33     }
34 };