008. String to Integer (atoi).cpp

class Solution {
public:
	int myAtoi(string str) {
		if (str.size() == 0) return 0;
		int cur = 0;
		while (cur < str.size() && str[cur] == ' ') cur++;
		if (cur == str.size() || (!isdigit(str[cur]) && str[cur] != '+' && str[cur] != '-')) return 0;
		int end = cur + 1;
		while (isdigit(str[end])) end++;
		string s = str.substr(cur, end - cur);
		int num = 0;
		int base = 1;
		for (int i = s.size() - 1; i >= 0; i--) {
			if (s[i] == '+' || s[i] == '-') break;
			int add = base * (s[i] - '0');
			if (INT_MAX - num < add || (s.size() - i > 10 && s[i] != '0'))
				return s[0] == '-' ? INT_MIN : INT_MAX;
			num += add;
			base *= 10;
		}
		if (s[0] == '-') num = -num;
		return num;
	}
};