# [Leetcode]8 : String to Integer (atoi)

Problem :
Implement the `myAtoi(string s)` function, which converts a string to a 32-bit signed integer (similar to C/C++'s `atoi` function).

The algorithm for `myAtoi(string s)` is as follows:
2. Check if the next character (if not already at the end of the string) is `'-'` or `'+'`. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present.
3. Read in next the characters until the next non-digit charcter or the end of the input is reached. The rest of the string is ignored.
4. Convert these digits into an integer (i.e. `"123" -> 123`, `"0032" -> 32`). If no digits were read, then the integer is `0`. Change the sign as necessary (from step 2).
6. If the integer is out of the 32-bit signed integer range `[-231, 231 - 1]`, then clamp the integer so that it remains in the range. Specifically, integers less than `-231` should be clamped to `-231`, and integers greater than `231 - 1` should be clamped to `231 - 1`.
7. Return the integer as the final result.

Note:
* Only the space character `' '` is considered a whitespace character.
* Do not ignore any characters other than the leading whitespace or the rest of the string after the digits.

Thoughts :
1. strip 用於移除整個字串的空格。
2. 使用re.findall()開始查找，使用正規表達式來找到+/-，到第一個非數字字符處停止。正規式為 “^[+-]?\d+”。
3. 把數字轉成整數(int)，python的int可以表示無限大的數字，不擔心越界。4. 若超出題目說的邊界，int_max或int_min邊界，則返回int_max或int_min。

Solution :

`class Solution:    def myAtoi(self, s: str) -> int:        s = s.strip()        if not s:            return 0        res = re.findall(r"^[+-]?\d+", s)        if not res:            return 0        res = int(res)        return max(min(res, 2**31 -1),-2**31)`

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