int myAtoi(string s) {

int i = 0;

int len = s.length();

int isPositive = true;

int result = 0;

while (i < len && s[i] == ' ') i++;

if (s[i] == '-' || s[i] == '+') {

if (s[i] == '-') isPositive = false;

i++;

}

while (i < len) {

char c = s[i];

if (!isdigit(c)) return result;

if (isPositive) {

if (result > INT_MAX / 10) return INT_MAX;

result *= 10;

int n = c - '0';

if (result > INT_MAX - n) return INT_MAX;

result += n;

} else {

if (result < INT_MIN / 10) return INT_MIN;

result *= 10;

int n = c - '0';

if (result < INT_MIN + n) return INT_MIN;

result -= n;

}

i++;

}

return result;

}