#define ADDITION  '+'

 #define SUBSTRACTION  '-'

 #define MULTIPLICATION  '*'

 #define DIVISION  '/'

 class Solution {

 public:

     set<char> tokenSet{'+', '-', '*', '/'};

     stack<int> num;

     int evalRPN(vector<string> &tokens) {

         for (auto &token : tokens) {

             auto iter = tokenSet.find( token[token.size()-] );

             if ( iter == tokenSet.end() ) {

                 num.push( atoi( token.c_str() ) );

             } else {

                int right = num.top();

                num.pop();

                int left = num.top();

                num.pop();

                switch ( *iter )

                {

                    case ADDITION :

                        num.push(left + right);

                        break;

                    case SUBSTRACTION:

                        num.push(left - right);

                        break;

                    case MULTIPLICATION:

                        num.push(left * right);

                        break;

                    case DIVISION:

                        num.push(left / right);

                        break;

                    default:

                        break;

                }

             }

         }

         int ret = num.top();

         num.pop();

         return ret;

     }

 };