[LeetCode]String to Integer (atoi)

题目描述:(链接)

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.

解题思路:

题目挺麻烦的，需要考虑很多情况。

class Solution {
public:
    int myAtoi(string str) {
        int len = str.size();
        if(len == 0) return 0;
        
        int sign = 1;
        int i = 0;
        
        while (str[i] == ' ') {  
            i++;  
        }
        
        // 符号
        if(str[i] == '+' || str[i] == '-') {
            if(str[i] == '+') {
                sign = 1;
            } else {
                sign = -1;
            }
            ++i;
        } 
        
        long ans = 0;
        while(isdigit(str[i])) {
            ans = ans * 10 + str[i] -'0';
            if(ans > INT_MAX) {
                return sign == 1 ? INT_MAX : INT_MIN;
            }
            ++i;
        }
        
        return ans * sign;
    }
};