[LeetCode]String to Integer (atoi)

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.

题目是Easy的题目，考虑的cases比较多。

各种没考虑到的情况，根据报错的case改代码就行了。

class Solution {
public:
    int myAtoi(string str) {
        if(str.length()==0) return 0;
        int result;
        long long temp=0;
        int flag=0;
        //正负号标志
        int sign=0;
        //是否已存在+-号，避免"-+86"类似这种出现
        int before_space=0;
        //空格前是否有数字标志，有数字返回数值，没数字continue
        for(int i=0;i<str.length();i++)
        {
            if(str[i]==' ')
            {
                if(before_space==0) continue;
                else break;
            }
            if((str[i]=='-')&&(sign==0))
            {
                flag=1;
                sign=1;
                before_space=1;
            }
            else if((str[i]=='+')&&(sign==0))
            {
                flag=0;
                sign=1;
                before_space=1;
            }
            else
            {
                before_space=1;
                if (str[i]<'0'||str[i]>'9')
                {
                    if(str[i]>='a'&&str[i]<='z')
                    {
                        break;
                    }
                    else 
                    {
                        return 0;
                    }
                }
                int number = str[i]-'0';
                if(number==0&&temp==0)
                {
                    continue;
                }
                temp = temp*10+number;
                if((temp>INT_MAX)&&(flag==0)) return INT_MAX;
                else if(((temp-1)>INT_MAX)&&(flag==1)) return INT_MIN;
            }
        }
        if(flag==1)
        {
            temp=-1*temp;
        }
        result=(int)temp;
        return result;
    }
};