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

逆波兰表达式，比较简单，不过我的代码有点复杂。。。如下：

int evalRPN(vector<string> &tokens) {
        stack<int> result;
        result.push( 0 );
        
        int one = 0, second = 0;
        for( int ix = 0; ix < tokens.size(); ++ix )
        {
            if( tokens[ ix ] == "+" )
            {
                one = result.top(), result.pop();
                second = result.top(), result.pop();
                result.push( second + one );
            }
            else if( tokens[ ix ] == "-" )
            {
                one = result.top(), result.pop();
                second = result.top(), result.pop();
                result.push( second - one );
            }
            else if( tokens[ ix ] == "*" )
            {
                one = result.top(), result.pop();
                second = result.top(), result.pop();
                result.push( second * one );
            }
            else if( tokens[ ix ] == "/" )
            {
                one = result.top(), result.pop();
                second = result.top(), result.pop();
                result.push( second / one );
            }
            else result.push( atoi( tokens[ ix ].c_str()));
        }
        return result.top();   
    }

有大婶代码： https://oj.leetcode.com/discuss/7494/my-accepted-c-solution