[LeetCode]8. String to Integer(atoi)

Description

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.

Discussion

常规操作。注意一下特殊符号的处理即可。

算法的时间复杂度为O(n)。

C++ Code

class Solution {public:    int myAtoi(string str) {        //空串返回0        if(str.length() == 0)        {            return 0;        }        //用一个long long类型的防止溢出        long long answer = 0;        //符号        int sign = 1;        int index = 0;        const int maxInt = 0x7fffffff;        const int minInt = 0x80000000;        //跳过空格        while(str[index] == ' ')        {            index++;        }        //记录符号，默认为正        if(str[index] == '+')        {            index++;        }        else if(str[index] == '-')        {            index++;            sign = -1;        }        //每次添加一位，并进行溢出判断。若遇到非数字字符，跳出并输出之前的数字。        for(int i = index; i < str.length(); i++)        {            if(str[i] >= '0' && str[i] <= '9')            {                answer = answer * 10 + str[i] - '0';                if(answer * sign > maxInt)                {                    return maxInt;                }                if(answer * sign < minInt)                {                    return minInt;                }            }            else            {                break;            }        }        answer = answer * sign;        return (int)answer;    }};