LeetCode: String to Integer (atoi)

这种题就是考你考虑了多少些情况，第一次没有考虑到的情况有：+-号，超出int范围，多数次过

class Solution {
public:
    int atoi(const char *str) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        bool showed = false;
        int s = 0;
        bool negtive = false;
        for (int i = 0; *(str+i) != '\0'; i++) {
            if (!showed) {
                if (*(str+i) == ' ') continue;
                if (*(str+i) >= '0' && *(str+i) <= '9') {
                    showed = true;
                    s = (int)(*(str+i) - '0');
                }
                else if (*(str+i) == '-') {
                    showed = true;
                    negtive = true;
                }
                else if (*(str+i) == '+') showed = true;
                else return 0;
            }
            else {
                if (*(str+i) == ' ') return negtive? -s : s;
                if (*(str+i) >= '0' && *(str+i) <= '9') {
                    if (s > (INT_MAX - (int)(*(str+i)-'0'))/10)
                        return negtive? INT_MIN : INT_MAX;
                    s = s*10 + (int)(*(str+i) - '0');
                }
                else return negtive? -s : s;
            }
        }
        return negtive? -s : s;
    }
};

 后来写了个更加精简的代码

class Solution {
public:
    int atoi(const char *str) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        while (isspace(*str)) str++;
        int ret = 0;
        bool isNeg = false;
        if (*str == '+') str++;
        if (*str == '-') {
            isNeg = !isNeg;
            str++;
        }
        while (isdigit(*str)) {
            if (ret > (INT_MAX - int(*str-'0'))/10) return isNeg? INT_MIN : INT_MAX;
            ret = ret*10+int(*str-'0');
            str++;
        }
        return isNeg? -ret : ret;
    }
};