字符串转换整数

class Solution {
public:
    int myAtoi(string s) {
        stringstream str(s);
        int n=0;
        str>>n;
        return n;
    }
};

class Solution {
public:
    int myAtoi(string s) {
        int i = 0, n = s.size(), sign = 1;
        long result = 0;

        //跳过前导空格
        while (i < n && s[i] == ' ') {
            i++;
        }

        //处理可选符号
        if (i < n && (s[i] == '+' || s[i] == '-')) {
            sign = (s[i] == '-') ? -1 : 1;
            i++;
        }

        //转换数字字符为整数
        while (i < n && isdigit(s[i])) {
            result = result * 10 + (s[i] - '0');
            if (result * sign >= INT_MAX) {
                return INT_MAX;
            } else if (result * sign <= INT_MIN) {
                return INT_MIN;
            }
            i++;
        }

        return result * sign;
    }
};