3.【字符串】Atoi--Accepted Java code

public int myAtoi(String str) {
if(str==null)
{
return 0;
}
str = str.trim();
if(str.length()==0)
return 0;
boolean isNeg = false;
int i = 0;
if(str.charAt(0)=='-' || str.charAt(0)=='+')
{
i++;
if(str.charAt(0)=='-')
isNeg = true;
}
int res = 0;
while(i<str.length())
{
if(str.charAt(i)<'0'||str.charAt(i)>'9')
break;
int digit = (int)(str.charAt(i)-'0');
if(isNeg && res>-((Integer.MIN_VALUE+digit)/10))
return Integer.MIN_VALUE;
else if(!isNeg && res>(Integer.MAX_VALUE-digit)/10)
return Integer.MAX_VALUE;
res = res*10+digit;
i++;
}
return isNeg?-res:res;
}