String to Integer (atoi)

1.trim

2.符号

3.overflow

public class Solution {
    public int atoi(String str) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(str == null)
            return 0;
        if(str.length() == 0)
            return 0;
        str = str.trim();
        boolean positive = true;
        long result = 0;
        if(str.charAt(0) == '-')
        {
            str = str.substring(1);
            positive = false;
        }
        else if(str.charAt(0) == '+')
        {
            str = str.substring(1);
        }
        for(int i=0;i<str.length();i++)
        {
            char tmp = str.charAt(i);
            if(tmp >= '0' && tmp <= '9')
                result = 10 * result + tmp - '0';
            else
                break;
        }
        if(result > Integer.MAX_VALUE)
            return positive?Integer.MAX_VALUE:Integer.MIN_VALUE;
        return positive?(int)result:(int)(-1*result);
    }
}