[Leetcode] 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.

别人的代码，很精简，值得学习。

class Solution {
public:
    int atoi(const char *str) {
        assert(str != NULL);  
        while(isspace(*str)) str++;  // remove ' '  
        
        int sign = (*str == '-') ? -1 : 1;  
        if (*str == '-' || *str == '+')    // if can check one char  
            str++;  
               
        int ret = 0;  
        while(isdigit(*str))   // is digit  
        {  
            int digit = *str - '0';  
               
            if (INT_MAX / 10 >= ret)  
                ret *= 10;  
            else  
                return sign == -1 ? INT_MIN : INT_MAX;  
                   
            if (INT_MAX - digit >= ret)  
                ret += digit;  
            else  
                return sign == -1 ? INT_MIN : INT_MAX;  
                   
            str++;  
        }  
           
        return ret * sign;  
    }
};