/*
* @lc app=leetcode.cn id=150 lang=cpp
*
* [150] 逆波兰表达式求值
*/
// @lc code=start
class Solution
{
public:
int calc(int left, int right, char sign)
{
switch (sign)
{
case '+':
return left + right;
case '-':
return left - right;
case '*':
return left * right;
case '/':
return left / right;
}
throw "";
}
int evalRPN(vector<string> &tokens)
{
stack<int> intStack;
for (string &str : tokens)
{
if (str.size() == 1 &&
(str[0] == '+' || str[0] == '-' || str[0] == '*' || str[0] == '/'))
{
// 遇到运算符,开始运算
int right = intStack.top();
intStack.pop();
int left = intStack.top();
intStack.pop();
intStack.push(calc(left, right, str[0]));
}
else
{
// 遇到数字,直接入数字栈
intStack.push(stoi(str));
}
}
return intStack.top();
}
};
// @lc code=end
