求逆波兰表达式的值

问题描述：

 

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

 

 

用逆波兰表示法计算算术表达式的值。             

有效运算符为+，-，*，/。每个操作数可以是整数或另一个表达式

 

 

问题解决(c\c++)：

class Solution {

public:

    int evalRPN(vector<string> &tokens) {

        stack<int> mystack;

        int size = tokens.size();

        int i = 0;

        for(; i< size; i++){

            if(tokens[i] == "+"){

                    a = mystack.top();

                    mystack.pop();

                    b = mystack.top() + a;

                    mystack.pop();

                    mystack.push(b);

            }

            else if(tokens[i] == "-"){

                    a = mystack.top();

                    mystack.pop();

                    b = mystack.top() - a;

                    mystack.pop();

                    mystack.push(b);

            }

            else if(tokens[i] == "*"){

                    a = mystack.top();

                    mystack.pop();

                    b = mystack.top() * a;

                    mystack.pop();

                    mystack.push(b);

            }

            else if(tokens[i] == "/"){

                    a = mystack.top();

                    mystack.pop();

                    b = mystack.top() / a;

                    mystack.pop();

                    mystack.push(b);

            }

            else{

                temp = atoi(tokens[i].c_str());

                mystack.push(temp);

            }

        }

        return mystack.top();

    }

 public:

    int a;

    int b;

    int temp;

    

};