leetcode[150]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:

  ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
  ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

class Solution {
public:
    int evalRPN(vector<string> &tokens) {
        if(tokens.empty())return INT_MIN;
        stack<int> sta;
        for(auto &tok :tokens)
        {
            if(tok!="+"&&tok!="-"&&tok!="*"&&tok!="/")
            {
                sta.push(atoi(tok.c_str()));
            }
            else 
            {
                int right=sta.top();
                sta.pop();
                int left=sta.top();
                sta.pop();
                int res=0;
                switch(tok[0])
                {
                    case '+':
                         res=left+right;
                         break;
                    case '-':
                         res=left-right;
                         break;
                    case '*':
                         res=left*right;
                         break;
                    case '/':
                         res=left/right;
                         break;
                    defaut  :break;
                }
                sta.push(res);
            }
        }
        return sta.top();
    }
};