把字符串转换成整数

1.不考虑溢出也能过[牛客测试不全面]

class Solution 
{ 
public:
	int StrToInt(string str) 
	{
		int answer = 0; 
		int isplus = 1;
		for (char& ch : str) 
		{ 
			if (ch == '+')
				isplus = 1;
			else if (ch == '-')
				isplus = - 1;
			else
			{
				if (ch < '1' || ch > '9')
					return 0;
				else
					answer = answer * 10 + ch - '0';
			}
		} 
		return isplus * answer;
	}
};

2.考虑溢出

class Solution 
{
public:
	int StrToInt(string str)
{
	int len = str.size();
	if (len == 0)
		return 0;

	int answer = 0;
	int flag = 1;
	for (char& ch : str)
	{
		if (ch == '+')
			flag = 1;
		else if (ch == '-')
			flag = -1;
		else
		{
			if (ch < '1' || ch > '9')
				return 0;
			else
			{
				answer = answer * 10 + ch - '0';
				if (
					(flag == 1 && answer > 0x7fffffff) 
				 || (flag == -1 && answer > 0x80000000)
				   )
					return 0;
			}
		}
	}
	return flag * answer;
}
};