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

 原题地址
class Solution {
public:
	int evalRPN(vector<string> &tokens) 
	{
		stack<int> result;
		vector<string>::const_iterator it = tokens.begin();
		int num1,num2,temp;
		while (it != tokens.end())
		{
			if( (*it != "*") && (*it != "+") && (*it != "-") && (*it != "/") )
			{
				result.push(atoi((*it).c_str()));
				it++;
			} 
			else
			{
				num2 =  result.top();
				result.pop();
				num1 = result.top();
				result.pop();
				if (*it == "+")
				{
					temp = num1 + num2;
					result.push(temp);
				}
				else if (*it == "-")
				{
					temp = num1 - num2;
					result.push(temp);
				}
				else if (*it == "*")
				{
					temp = num1 * num2;
					result.push(temp);
				}
				else if (*it == "/")
				{
					temp = num1 / num2;
					result.push(temp);
				}
				it++;
			}
		}
		return result.top();
	}
};


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