leetcode 8. String to Integer (atoi)

class Solution {public:    int myAtoi(string str) {        string x = "";                int n = str.length();        int l=0,r=n-1;        while(str[l]==' '&&l<n)l++;        while(str[r]==' '&&r>0)r--;        int be =0;        if(str[l] == '+' || str[l] == '-')             be=1;             long long ans = 0;        int flag = 1;        if(str[l] == '-') flag = -1;        for(int i = be+l;i <= r; i++){            if(str[i] < '0' || str[i] > '9') break;            ans = ans*10+str[i]-'0';            if(ans > 2147483647 && flag == 1) return 2147483647;            else if(ans > 2147483648 && flag == -1) return -2147483648;        }        return ans*flag;    }};