// String to Integer (atoi)

// 时间复杂度O(n)，空间复杂度O(1)

class Solution {

public:

int myAtoi(const string &str) {

int num = 0;

int sign = 1;

const int n = str.length();

if (n == 0) return 0;

int i = 0;

while (str[i] == ' ' && i < n) i++;

if (str[i] == '+') {

i++;

} else if (str[i] == '-') {

sign = -1;

i++;

}

for (; i < n; i++) {

if (str[i] < '0' || str[i] > '9')

break;

if (num > INT_MAX / 10 ||

(num == INT_MAX / 10 &&

(str[i] - '0') > INT_MAX % 10)) {

return sign == -1 ? INT_MIN : INT_MAX;

}

num = num * 10 + str[i] - '0';

}

return num * sign;

}

};