class Solution {
public:
    int myAtoi(string s) {
        int k=0;
        while(k<s.size()&&s[k]==' ') k++;//去除前置空格
        if(k==s.size()) return 0;

        int minus=1;//判断正负
        if(s[k]=='-') minus=-1,k++;
        else if(s[k]=='+') k++;

        long long res=0;
        while(k<s.size()&&s[k]>='0'&&s[k]<='9')
        {
            res=res*10+s[k]-'0';
            k++;
            if(res>INT_MAX) break;
        }

        res*=minus;
        if(res>INT_MAX) return INT_MAX;
        if(res<INT_MIN) return INT_MIN;
        return res;
    }
};