String to Integer

String to Integer

问题：

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

思路：

　　只是需要考虑的corner case多一些，思路很简单

我的代码：

public class Solution {
    public int myAtoi(String str) {
        if(str==null || str.length()==0 || str.trim().length()==0)  return 0;
        str = str.trim();
        boolean isPlus = true;
        if(str.charAt(0) == '-')
        {
            isPlus = false;
            str = str.substring(1);
        }
        else
        {
            if(str.charAt(0) == '+')
                str = str.substring(1);
        }
        long rst = 0;
        for(int i=0; i<str.length(); i++)
        {
            char c = str.charAt(i);
            if(isValidNum(c))
            {
                rst = rst*10 + (c-'0');
                long tmp = (isPlus ? rst : rst*-1);
                if(tmp>Integer.MAX_VALUE)   return Integer.MAX_VALUE;
                if(tmp<Integer.MIN_VALUE)   return Integer.MIN_VALUE;
            }
            else 
                break;
        }
        rst = (isPlus ? rst : rst*-1);
        return (int)rst;
    }
    public boolean isValidNum(char c)
    {
        return c<='9' && c>='0' ? true : false; 
    }

}