8. String to Integer (atoi)

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.

Update (2015-02-10):
The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.

解答：
这是二刷时的结果了，我自己做出来了，找不到之前的博客文章了，就重新写一下。感觉这些testcase 有点变态，但是可以作为参考吧。

比如+-2
0a123
0 123
等等

class Solution {
public:
    int myAtoi(string str) {
        long long result=0;
        int len=str.size();
        int sign=1;
        bool mark=false;
        int i=0;
        for(;i<len;i++)
        {
            if(str[i]==' ') continue;
            else break;
        }
        for(;i<len;i++)
        {

            if(str[i]=='-'){if(mark==true)return false;else{sign=-1;mark=true;}continue;}
            if(str[i]=='+'){if(mark==true)return false;else mark=true;continue;};
            if(str[i]<='9'&&str[i]>='0')
            {
                result=result*10+str[i]-'0';
                if(sign*result>=INT_MAX) return INT_MAX;
                if(sign*result<=INT_MIN) return INT_MIN;
            }
            else 
                return sign*result;

        }
        return sign*result;


    }
};