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# String to Integer (atoi)（转换到整型）

atoi 的要求：

## 原文

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.

（好吧，在写博客，也就上面的翻译过程中，我发现题目懂了……）

public class Solution
{
public int MyAtoi(string str)
{
if (string.IsNullOrEmpty(str))
{
return 0;
}
var result = 0;
var i = 0;
// clean all the whitespaces in the beginning
while (i < str.Length && str[i] == ' ')
{
i++;
}
// check positive or negative sign
var sign = 1;
switch (str[i])
{
case '-':
sign = -1;
i++;
break;
case '+':
sign = 1;
i++;
break;
}
// check the rest of numbers
while (i < str.Length && str[i] >= '0' && str[i] <= '9')
{
// check overflow
try
{
checked
{
result = result * 10 + (str[i++] - '0');
}
}
catch (OverflowException)
{
return sign == 1 ? int.MaxValue : int.MinValue;
}
}
return sign * result;
}
}
1045 / 1045 test cases passed.
Status: Accepted
Runtime: 168 ms
Your runtime beats 16.85% of csharp submissions.