LeetCode 8. String to Integer (atoi)

题目描述

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.

题目解析

将字符串转化为int整型。

注意考虑各种可能的字符串输入。

代码

class Solution {
public:
int myAtoi(string str) {
long long ans=0;//输入空字符串输出为零
int sign=1,sign_flag=0,cnt=0;
for(int i=0;i<str.size()&&cnt<11;i++)//考虑str过长超过long long，用cnt计数数字长度
{
if(str[i]=='-'&&sign_flag==0)  //考虑-前可以有空格
{
sign=-1;
sign_flag=1;
continue;
}
else if(str[i] == '+'&&sign_flag==0)//考虑出现+号
{
sign_flag=1;
continue;
}
else if(str[i]==' '&&sign_flag==0)//考虑数字前面可以有空格，但是中间不能有空格
{
continue;
}
else if(str[i]>'9'||str[i]<'0')//遇到非数字就跳出
{
break;
}
sign_flag=1;
ans = ans*10 + str[i] - '0';
cnt++;
}
ans *= sign;
if(ans>INT_MAX)//如果溢出，输出正负两边的极限
{
return INT_MAX;
}
else if(ans<INT_MIN)
{
return INT_MIN;
}
else
{
return (int)ans;
}
}
};