LeetCode(8) String To Integer(atoi)

题目如下：

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.

分析如下：

处理各种invalid input要仔细，详见下面的代码。

我的代码：

//64ms
class Solution {
public:
    int atoi(const char *str) {
        //space
        //validate 0~9
        //+-
        //0012 vs 1002
        //INTMAX
        int result = 0;
        bool isNegative = false;
        while(*str == ' ') 
            str++;
        if(*str == '+') 
            str++;
        else if(*str == '-') {
            isNegative = true;
            str++;
        }
        while(*str != '\0') {
            if (*str - '0' == 0 && result == 0) {
                str++;
                continue;
            }
            if (*str - '0' < 0 || *str - '9' > 0)
                return isNegative? -result: result;
            if (result > INT_MAX / 10)
                return isNegative? INT_MIN : INT_MAX;
            result *= 10;
            if ((*str - '0') > (INT_MAX - result))
                return isNegative? INT_MIN : INT_MAX;
            result = result + *str - '0';
            str++;
        }
        return isNegative? -result : result;
    }
};