1 class Solution {
2 public:
3 void parseNum(stack<int>& _stack, const string & token){
4 int number = atoi(token.c_str());
5 _stack.push(number);
6 }
7 void parseOperation(stack<int> & _stack, char token){
8 int num1 = _stack.top();
9 _stack.pop();
10 int num2 = _stack.top();
11 _stack.pop();
12 int rlt = 0;
13 switch(token){
14 case '+':
15 rlt= num2+num1;
16 break;
17 case '-':
18 rlt = num2-num1;
19 break;
20 case '*':
21 rlt= num2*num1;
22 break;
23 case '/':
24 rlt = num2/num1;
25 break;
26 }
27 _stack.push(rlt);
28 }
29 int evalRPN(vector<string> &tokens) {
30 stack<int> _stack;
31 vector<string>::iterator itr;;
32 for (itr=tokens.begin(); itr!=tokens.end(); itr++){
33 string token = * itr;
34 if (token.length()==1){
35 char c = token.at(0);
36 if (c=='+' || c=='-' || c=='*' || c=='/')
37 parseOperation(_stack, c);
38 else parseNum(_stack, token);
39 }
40 else parseNum(_stack, token);
41 }
42 if (!_stack.empty())
43 return _stack.top();
44 return 0;
45 }
46 };
