剑指 Offer II 036. 后缀表达式

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        stack<int> num;
        int size=tokens.size();
        for(int i =0;i<size;++i){
            string& token  = tokens[i];
            if(token.size()>1||isdigit(*token.c_str())){
                num.push(atoi(token.c_str()));
            }else{
                int num2=num.top();
                num.pop();
                int num1=num.top();
                num.pop();
                switch (token[0])
                {
                case '+':
                    num.push(num1+num2);
                    break;
                case '*':
                    num.push(num1*num2);
                    break;
                case '-':
                    num.push(num1-num2);
                    break;
                case '/':
                    num.push(num1/num2);
                    break;
                }
            }
        }
        return num.top();
    }
};