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.

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class Solution {
public:
    int myAtoi(string str) {
        int len = str.length();
        if (!len) return 0;
        int i = 0;
        while (i < len && str[i] == ' ') i++;
        if (i == len) return 0; // string contains only whitespace
        int pos = 1; // indicates whether it is an positive integer
        if (str[i] == '-') {
            pos = 0; // s[i] is the first non-whitespace character
            i++;
        }
        else if (str[i] == '+') i++;
        int out = 0;
        while (i < len) {
            int temp = (int)(str[i] - '0');
            if (temp < 0 || temp > 9) return (pos ? out : -out);
            else {
                int temp2 = out * 10 + temp;
                if (temp2 / 10 != out) return (pos ? INT_MAX : INT_MIN); // avoid overflow
                else out = temp2;
            }
            i++;
        }
        return (pos ? out : -out);
    }
};