#150. Evaluate Reverse Polish Notation

# Intuition
<!-- Describe your first thoughts on how to solve this problem. -->

# Approach
<!-- Describe your approach to solving the problem. -->

# Complexity
- Time complexity:
<!-- Add your time complexity here, e.g. $$O(n)$$ -->
          Time Complexity =  O(n)

- Space complexity:
<!-- Add your space complexity here, e.g. $$O(n)$$ -->
          Space Complexity = O(n)

# Code
```
/*
 #150. Evaluate Reverse Polish Notation

 
 



*/
class Solution {
public:

    bool checkifoper(string c) {
        if(c=="+" || c=="-" || c=="*" || c=="/") return true;
        else  return false;
    }

    int evalRPN(vector<string>& tokens) {
        stack <int> s;
        
        for(int i = 0; i < tokens.size(); i++) {
            if(!checkifoper(tokens[i])) s.push(stoi(tokens[i]));
            else {
                long int num1=s.top();
                s.pop();
                long int num2=s.top();
                s.pop();
                if(tokens[i]=="+")  s.push(num1 + num2);
                if(tokens[i]=="-")  s.push(num2 - num1);
                if(tokens[i]=="/")  s.push(num2 / num1);
                if(tokens[i]=="*")  s.push(num2 * num1);
            }
        } return s.top();
    }
};
```