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.

比较简单的题目, 因为要转换的是整数, 因此只需要考虑前导空格和符号.

代码:

class Solution {
public:
    bool isNumber(char a){
        return a >= '0' && a <= '9';
    }

    int myAtoi(string str) {
        int len = str.length(), p = 0;
        if(str[0] == ' '){
            for(int i = 0; str[i] == ' '; i++) p++;
        }
        if(!(isNumber(str[p]) || str[p] == '-' || str[p] == '+'))
            return 0;
            
        int sign = 1;
        if(str[p] == '-'){
            sign = -1;
        }
        
        if(str[p] == '-' || str[p] == '+')
            p++;
            
        long long re = 0;
        len = str.length();
        for(int i = p; i < len && isNumber(str[i]); i++){
            re *= 10;
            re += str[i] - '0';
            
            if(sign > 0 && re > INT_MAX)
                return INT_MAX;
            if(sign < 0 && -re < INT_MIN)
                return INT_MIN;
        }
        
        return sign * re;
    }
};