LeetCode | 8) String to Integer (atoi)

最新推荐文章于 2025-08-09 17:01:50 发布

wuhuancheng

最新推荐文章于 2025-08-09 17:01:50 发布

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分类专栏： leetcode 文章标签： string interger leetcode

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8 篇文章

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本文介绍了一种将字符串转换为整数的有效方法，并提供了一个C++实现示例。该方法考虑了各种输入情况，包括正负号处理、非数字字符忽略及整数溢出等问题。

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题目

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.

Requirements for atoi:

The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. 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.

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.

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.

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.

prototype

class Solution {
public:
    int myAtoi(string str) {

};

思路

很简单，注意溢出情况即可

代码

class Solution {
public:
    int myAtoi(string str) {
        int sum{0}, flag{1};
        int i{str.find_first_not_of(' ')};
        if (str[i] == '-') {flag = -1; ++i;}
        else if (str[i] == '+') {++i;}
        while (isdigit(str[i]))
        {
            if (sum <= (INT_MAX - (str[i] - '0'))/10)
                sum = sum * 10 + (str[i++] - '0');
            else
                return flag > 0 ? INT_MAX : INT_MIN;
        }
        return flag*sum;
    }
};

运行时间9ms