[LeetCode]Evaluate Reverse Polish Notation

 1 class Solution {
 2 public:
 3     /* 1 for numbers */
 4     int isNumber(string &input, int *number){
 5         int length = input.length();
 6         int tmp = 1;
 7         *number = 0;
 8         
 9         for(int i = length - 1; i >= 0; i--){
10             if(input[i] >= ‘0‘ && input[i] <= ‘9‘){
11                 *number += (input[i] - ‘0‘) * tmp;
12                 tmp *= 10;
13             }
14             else if(*number != 0 && input[i] == ‘-‘){
15                 *number *= -1;
16             }
17             else
18             {
19                 return 0;
20             }
21         }
22 
23         return 1;
24     }
25     
26     int evalRPN(vector<string> &tokens) {
27         stack<int> tmpToken;
28         int currNumber = 0;
29         int leftNumber, rightNumber;
30         string tmpString;
31         
32         for(int i = 0; i < tokens.size(); i++){
33             tmpString = tokens[i];
34             
35             if(1 == isNumber(tmpString, &currNumber)){
36                 tmpToken.push(currNumber);
37             }else{
38                  rightNumber = tmpToken.top();
39                  tmpToken.pop();
40                  leftNumber = tmpToken.top();
41                  tmpToken.pop();
42                  switch(tmpString[0]){
43                     case ‘+‘:
44                         tmpToken.push(leftNumber + rightNumber);
45                         break;
46                     case ‘-‘:
47                         tmpToken.push(leftNumber - rightNumber);
48                         break;
49                     case ‘*‘:
50                         tmpToken.push(leftNumber * rightNumber);
51                         break;
52                     case ‘/‘:
53                         tmpToken.push(leftNumber / rightNumber);
54                         break;   
55                     default:
56                         return -1;
57                         break;
58                  }
59             }
60                
61         }
62         
63         return(tmpToken.top());
64     }
65 };