class Solution {
public:
    int strToInt(string str) {
       int k=0;  //字符串的head
       while(k<str.size()&&str[k]==' ') k++;
       bool is_minus =false;
       long long num=0;
       if(str[k]=='+') k++;
       else if(str[k]=='-') is_minus=true,k++;
       while(k<str.size()&&str[k]>='0'&&str[k]<='9'){
           num =num*10+(str[k]-'0');
           k++;
       }
       if(is_minus) num*=-1;
       if(num > INT_MAX) num = INT_MAX;
        if(num < INT_MIN) num = INT_MIN;
        return (int) num;
    }
};