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.

Solution

class Solution {
public:
    int myAtoi(string str) {
        long result = 0;
        int n = str.size(), i0 = 0;
        bool isNeg = false;
        while ( i0 != n and str[i0] == ' ' ) i0 += 1;
        char c = str[i0];
        if ( c == '+' ) i0 += 1;
        if ( c == '-' ) {
            isNeg = true;
            i0 += 1;
        }
        for ( int i = i0; i < n; i++ ) {
            if ( str[i] - '0' > 10 or str[i] - '0' < 0 ) return result*(1-2*isNeg);
            if ( not isNeg ) {
                if ( result < (INT_MAX - (str[i]-'0'))/10.) result = result*10 + str[i] - '0';
                else return INT_MAX;
            }
            else {
                if ( result < -((INT_MIN + str[i]-'0')/10.) ) result = result*10 + str[i] - '0';
                else return INT_MIN;
            }
        }
        return result*(1-2*isNeg);
    }
};

Notes
OVERFLOW bugs me!好好总结处理overflow的细节。。。