LeetCode Evaluate Reverse Polish Notation

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Some examples:

这个叫什么来着，好熟悉，逆波兰表达式？？？这个题目当然是极其简单的

class Solution {
public:
    int Opr(int x,int y,string opr){
        if(opr=="+"){
            return x+y;
        }
        if(opr=="-"){
            return x-y;
        }
        if(opr=="/"){
            return x/y;
        }
        if(opr=="*"){
            return x*y;
        }
    }
    int evalRPN(vector<string>& tokens) {
        stack<int>Int;
        int len=tokens.size();
        for(int i=0;i<len;i++){
            if(tokens[i]=="+"||tokens[i]=="-"||tokens[i]=="/"||tokens[i]=="*"){
                int x=Int.top();Int.pop();
                int y=Int.top();Int.pop();
                Int.push(Opr(y,x,tokens[i]));
            }else{
                Int.push(atoi(tokens[i].c_str()));
            }
        }
        return Int.top();
    }
};