string to integer

public class Solution{
	public int myAtoi(String str){
		int index = 0;
		int len = str.length();
		int sign = 1;
		int total = 0;
		//排除String为空的情况
		if(len == 0)
		return 0;
		
		//排除String开始为空字符的情况
		while(str.charAt(index) == ' ')
		index++;
		
		//确定首个非空字符正负符号
		if(str.charAt(index) == '+' || str.charAt(index) == '-'){}
		sign = str.charAt(index) == '+' ? 1 : -1;
		index++;
		}
		
		//reverse
		while(index < len ){
			int digit = str.charAt(index) - '0';
			if(digit < 0 || digit > 9)
			break;
			
			//检查是否有溢出情况,要记住这种巧妙地方法
			if(total > Integer.MAX_VALUE / 10 || total == Integer.MAX_VALUE / 10 && digit > Integer.MAX_VALUE % 10)
			return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
			
			total = total*10 + digit;
			index++;
		}
		return total*sign;
	}
}