8. String to Integer (atoi)

This is "easy" for programming if you are clear about all possible cases. Need to get the requirment clarified from the interviewer. Anyway, here are the cases that OJ thinks of (I've added comments for the cases in the code).

1:  class Solution {  
2:  public:  
3:    int myAtoi(string str) {  
4:      int i = 0, n = str.size();  
5:      long long res = 0;  
6:      int sign = 1;  
7:      // ignore leading spaces  
8:      while (str[i] == ' ') i++;  
9:      // process leading sign  
10:      if (str[i] == '-') { sign = -1; i++; }  
11:      else if (str[i] == '+') { sign = 1; i++; }  
12:      while (i < n && isNum(str[i])) {  
13:        res = res*10 + str[i]-'0';  
14:        // process overflow;  
15:        if (sign == 1 && res > INT_MAX) return INT_MAX;  
16:        if (sign == -1 && -res < INT_MIN) return INT_MIN;  
17:        i++;  
18:      }  
19:      return res * sign;  
20:    }  
21:    bool isNum(char c) {  
22:      return c >= '0' && c <= '9';  
23:    }  
24:  };