String to Integer (atoi)

题目描述

解题思路

题目要求将一个字符串转换成整数，难度一般，主要是对于输入情况以及返回值情况的考虑比较多，根据题目要求主要有以下几点：

1. The function first discards as many whitespace characters as necessary until the first non-whitespace character is found
2. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value
3. The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function
4. If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed
5. If no valid conversion could be performed, a zero value is returned. If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned。

c++代码实现

class Solution {public:    int myAtoi(string str) {        if (str.empty()) return 0;        int sign = 1, base = 0, i = 0;        while (i < str.length() && str[i] == ' ') ++i;        if (str[i] == '+' || str[i] == '-') {            sign = (str[i++] == '+') ? 1 : -1;        }        while (i < str.length() && (str[i] >= '0' && str[i] <= '9')) {            if (base > INT_MAX / 10 || (base == INT_MAX / 10 && str[i] - '0' > 7)) {                return (sign == 1) ? INT_MAX : INT_MIN;            }            base = 10 * base + (str[i++] - '0');        }        return base * sign;    }};

运行结果：

反思与总结

此题难度一般，主要是考虑输入情况的多样性，而这题情况其实还算蛮少的，这里有一篇对于是否是数字的详细的验证，考虑的十分全面，值得学习。