8. String to Integer (atoi)

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

Update (2015-02-10):
The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.

spoilers alert... click to show requirements for atoi.

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 1 class Solution {
 2 public:
 3     int myAtoi(string str) {
 4         int len = str.length();
 5         if (!len) return 0;
 6         int i = 0;
 7         while (i < len && str[i] == ' ') i++;
 8         if (i == len) return 0; // string contains only whitespace
 9         int pos = 1; // indicates whether it is an positive integer
10         if (str[i] == '-') {
11             pos = 0; // s[i] is the first non-whitespace character
12             i++;
13         }
14         else if (str[i] == '+') i++;
15         int out = 0;
16         while (i < len) {
17             int temp = (int)(str[i] - '0');
18             if (temp < 0 || temp > 9) return (pos ? out : -out);
19             else {
20                 int temp2 = out * 10 + temp;
21                 if (temp2 / 10 != out) return (pos ? INT_MAX : INT_MIN); // avoid overflow
22                 else out = temp2;
23             }
24             i++;
25         }
26         return (pos ? out : -out);
27     }
28 };